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Delaware

Delaware is a state in the Mid-Atlantic region of the United States. It borders Maryland to its south and west, Pennsylvania to its north, New Jersey to its northeast, and the Atlantic Ocean to its east. The state's name derives from the adjacent Delaware Bay, which in turn was named after Thomas West, 3rd Baron De La Warr, an English nobleman and the Colony of Virginia's first colonial-era governor.

Delaware occupies the northeastern portion of the Delmarva Peninsula, and some islands and territory within the Delaware River. It is the 2nd smallest and 6th least populous state, but also the 6th most densely populated. Delaware's most populous city is Wilmington, and the state's capital is Dover, the 2nd most populous city in Delaware. The state is divided into three counties, the fewest number of counties of any of the 50 U.S. states; from north to south, the three counties are: New Castle County, Kent County, and Sussex County. The southern two counties, Kent and Sussex counties, historically have been predominantly agrarian economies. New Castle is more urbanized and is considered part of the Delaware Valley metropolitan statistical area that surrounds and includes Philadelphia, the nation's sixth most populous city. Delaware is considered part of the Southern United States by the U.S. Census Bureau, but the state's geography, culture, and history are a hybrid of the Mid-Atlantic and Northeastern regions of the country.

Before Delaware coastline was explored and developed by Europeans in the 16th century, the state was inhabited by several Native American tribes, including the Lenape in the north and Nanticoke in the south. The state was first colonized by Dutch traders at Zwaanendael, near present-day Lewes, Delaware, in 1631. Delaware was one of the Thirteen Colonies that participated in the American Revolution and American Revolutionary War, in which the American Continental Army, led by George Washington, defeated the British, ended British colonization and established the United States as a sovereign and independent nation. On December 7, 1787, Delaware was the first state to ratify the Constitution of the United States, earning it the nickname "The First State".

Since the turn of the 20th century, Delaware has become an onshore corporate haven whose corporate laws are deemed appealing to corporations; over half of all New York Stock Exchange-listed corporations and over three-fifths of the Fortune 500 are legally incorporated in the state.

Etymology
Delaware was named after Delaware Bay, which in turn derived its name from Thomas West, 3rd Baron De La Warr (1577–1618), the first governor of the Colony of Virginia. The Delaware people, a name used by Europeans for Lenape people Indigenous to the Delaware Valley, also derive their name from the same source.

The name de La Warr is from Sussex and of Anglo-French origin. It came probably from a Norman lieu-dit La Guerre. This toponymic likely derived from Latin ager, the Breton gwern or from the Late Latin varectum (fallow). The toponyms Gara, Gare, Gaire, (the sound [ä] often mutated in [æ]) also appear in historical texts cited by Lucien Musset, where the word ga(i)ra means gore. It could also be linked with a patronymic from the Old Norse verr.

Native Americans
Before Delaware was settled by European colonists, the present-day state was home to the Eastern Algonquian tribes known as the Unami Lenape, or Delaware, who lived mostly along the coast, and the Nanticoke who occupied much of the southern Delmarva Peninsula. John Smith also shows two Iroquoian tribes, the Kuskarawock and Tockwogh, living north of the Nanticoke—they may have held small portions of land in the western part of the state before migrating across the Chesapeake Bay. The Kuskarawocks were most likely the Tuscarora.

The Unami Lenape in the Delaware Valley were closely related to Munsee Lenape tribes along the Hudson River. They had a settled hunting and agricultural society, and they rapidly became middlemen in an increasingly frantic fur trade with their ancient enemy, the Minqua or Susquehannock. With the loss of their lands on the Delaware River and the destruction of the Minqua by the Iroquois of the Five Nations in the 1670s, the remnants of the Lenape who wished to remain identified as such left the region and moved over the Allegheny Mountains by the mid-18th century. Generally, those who did not relocate out of the state of Delaware were baptized, became Christian and were grouped together with other persons of color in official records and in the minds of their non-Native American neighbors.

Colonial Delaware
The Dutch were the first Europeans to settle in present-day Delaware in the middle region by establishing a trading post at Zwaanendael, near the site of Lewes in 1631. Within a year, all the settlers were killed in a dispute with Native American tribes living in the area. In 1638, New Sweden, a Swedish trading post and colony, was established at Fort Christina (now in Wilmington) by Peter Minuit at the head of a group of Swedes, Finns and Dutch. The colony of New Sweden lasted 17 years. In 1651, the Dutch, reinvigorated by the leadership of Peter Stuyvesant, established a fort at present-day New Castle and, in 1655, they conquered the New Sweden colony, annexing it into the Dutch New Netherland. Only nine years later, in 1664, the Dutch were conquered by a fleet of English ships by Sir Robert Carr under the direction of James, the Duke of York. Fighting off a prior claim by Cecil Calvert, 2nd Baron Baltimore, Proprietor of Maryland, the Duke passed his somewhat dubious ownership on to William Penn in 1682. Penn strongly desired access to the sea for his Pennsylvania province and leased what then came to be known as the "Lower Counties on the Delaware" from the Duke.

Penn established representative government and briefly combined his two possessions under one General Assembly in 1682. However, by 1704 the province of Pennsylvania had grown so large their representatives wanted to make decisions without the assent of the Lower Counties, and the two groups of representatives began meeting on their own, one at Philadelphia, and the other at New Castle. Penn and his heirs remained proprietors of both and always appointed the same person Governor for their province of Pennsylvania and their territory of the Lower Counties. The fact that Delaware and Pennsylvania shared the same governor was not unique; from 1703 to 1738, New York and New Jersey shared a governor. Massachusetts and New Hampshire also shared a governor for some time.

Dependent in early years on indentured labor, Delaware imported more slaves as the number of English immigrants decreased with better economic conditions in England. The colony became a slave society and cultivated tobacco as a cash crop, although English immigrants continued to arrive.

American Revolution
Like the other middle colonies, the Lower Counties on the Delaware initially showed little enthusiasm for a break with Britain. The citizenry had a good relationship with the Proprietary government, and generally were allowed more independence of action in their Colonial Assembly than in other colonies. Merchants at the port of Wilmington had trading ties with the British.

New Castle lawyer Thomas McKean denounced the Stamp Act in the strongest terms, and Kent County native John Dickinson became the "Penman of the Revolution". Anticipating the Declaration of Independence, Patriot leaders Thomas McKean and Caesar Rodney convinced the Colonial Assembly to declare itself separated from British and Pennsylvania rule on June 15, 1776. The person best representing Delaware's majority, George Read, could not bring himself to vote for a Declaration of Independence. Only the dramatic overnight ride of Caesar Rodney gave the delegation the votes needed to cast Delaware's vote for independence.

Initially led by John Haslet, Delaware provided one of the premier regiments in the Continental Army, known as the "Delaware Blues" and nicknamed the "Blue Hen's Chicks". In August 1777 General Sir William Howe led a British army through Delaware on his way to a victory at the Battle of Brandywine and capture of the city of Philadelphia. The only real engagement on Delaware soil was the Battle of Cooch's Bridge, fought on September 3, 1777, at Cooch's Bridge in New Castle County, although there was a minor Loyalist rebellion in 1778.

Following the Battle of Brandywine, Wilmington was occupied by the British, and State President John McKinly was taken prisoner. The British remained in control of the Delaware River for much of the rest of the war, disrupting commerce and providing encouragement to an active Loyalist portion of the population, particularly in Sussex County. Because the British promised slaves of rebels freedom for fighting with them, escaped slaves flocked north to join their lines.

Following the American Revolution, statesmen from Delaware were among the leading proponents of a strong central United States with equal representation for each state.

Slavery and race
Many colonial settlers came to Delaware from Maryland and Virginia, where the population had been increasing rapidly. The economies of these colonies were chiefly based on labor-intensive tobacco and increasingly dependent on African slaves because of a decline in working class immigrants from England. Most of the English colonists had arrived as indentured servants (contracted for a fixed period to pay for their passage), and in the early years the line between servant and slave was fluid.

Most of the free African-American families in Delaware before the Revolution had migrated from Maryland to find more affordable land. They were descendants chiefly of relationships or marriages between white servant women and enslaved, servant or free African or African-American men. Under slavery law, children took the social status of their mothers, so children born to white women were free, regardless of their paternity, just as children born to enslaved women were born into slavery. As the flow of indentured laborers to the colony decreased with improving economic conditions in England, more slaves were imported for labor and the caste lines hardened.

By the end of the colonial period, the number of enslaved people in Delaware began to decline. Shifts in the agriculture economy from tobacco to mixed farming resulted in less need for slaves' labor. In addition local Methodists and Quakers encouraged slaveholders to free their slaves following the American Revolution, and many did so in a surge of individual manumissions for idealistic reasons. By 1810, three-quarters of all blacks in Delaware were free. When John Dickinson freed his slaves in 1777, he was Delaware's largest slave owner with 37 slaves. By 1860, the largest slaveholder owned 16 slaves.

Although attempts to abolish slavery failed by narrow margins in the legislature, in practical terms the state had mostly ended the practice. By the 1860 census on the verge of the Civil War, 91.7% of the black population were free; 1,798 were slaves, as compared to 19,829 "free colored persons".

An independent black denomination was chartered in 1813 by freed slave Peter Spencer as the "Union Church of Africans". This followed the 1793 establishment in Philadelphia of the African Methodist Episcopal Church by Richard Allen, which had ties to the Methodist Episcopal Church until 1816. Spencer built a church in Wilmington for the new denomination. This was renamed as the African Union First Colored Methodist Protestant Church and Connection, more commonly known as the A.U.M.P. Church. In 1814, Spencer called for the first annual gathering, known as the Big August Quarterly, which continues to draw members of this denomination and their descendants together in a religious and cultural festival.

Delaware voted against secession on January 3, 1861, and so remained in the Union. While most Delaware citizens who fought in the war served in the regiments of the state, some served in companies on the Confederate side in Maryland and Virginia Regiments. Delaware is notable for being the only slave state from which no Confederate regiments or militia groups were assembled. Delaware essentially freed the few slaves who were still in bondage shortly after the Civil War but rejected the 13th, 14th, and 15th Amendments to the Constitution; the 13th Amendment was rejected on February 8, 1865, the 14th Amendment was rejected on February 8, 1867, and the 15th Amendment was rejected on March 18, 1869. Delaware officially ratified the 13th, 14th, and 15th amendments on February 12, 1901.

Reconstruction and industrialization
During the Reconstruction Era that followed the Civil War, Democratic Redeemer governments led by the South's Bourbon aristocracy continued to dominate the region and imposed explicitly white supremacist regimes in the former slave states. The Delaware legislature declared Black people to be second-class citizens in 1866, and restricted their voting rights despite the 15th Amendment, ensuring continued Democratic success in the state throughout most of the 19th century. Fearful that the 1875 Civil Rights Act passed by Congress might establish racial equality, Delaware legislators passed Jim Crow laws that mandated segregation in public facilities. The state's educational system was segregated by operation of law. Delaware's segregation was written into the state constitution, which, while providing at Article X, Section 2, that "no distinction shall be made on account of race or color", nonetheless required that "separate schools for white and colored children shall be maintained."

Beginning in the late 19th century, the Wilmington area grew into a manufacturing center. Investment in manufacturing in the city grew from $5.5 million in 1860 to $44 million in 1900. The most notable manufacturer in the state was the chemical company DuPont, which to this day is heavily credited with making the state what it is today in many ways. Because of Wilmington's growth, local politicians from the city and New Castle County pressured the state government to adopt a new constitution providing the north with more representation. However, the subsequent 1897 constitution did not proportionally represent the north and continued to give the southern counties disproportionate influence.

As manufacturing expanded, businesses became major players in state affairs and funders of politicians through families such as the Du Ponts. Republican John Addicks attempted to buy a US Senate seat multiple times in a rivalry with the Du Ponts until the passage of the 17th Amendment. The allegiance of industries with the Republican party allowed them to gain control of the state's governorship throughout most of the 20th century. The GOP ensured black people could vote because of their general support for Republicans and thus undid restrictions on Black suffrage.

Delaware benefited greatly from World War I because of the state's large gunpowder industry. DuPont, the most dominant business in the state by WWI, produced an estimated 40% of all gunpowder used by the Allies during the war. It produced nylon in the state after the war and began investments into General Motors. Additionally, the company invested heavily in the expansion of public schools in the state and colleges such as the University of Delaware in the 1910s and 1920s. This included primary and secondary schools for Black people and women. Delaware suffered less during the Great Depression than other states, but the depression spurred further migration from the rural south to urban areas.

World War II to present
Like in World War I, the state enjoyed a big stimulus to its gunpowder and shipyard industries in World War II. New job opportunities during and after the war in the Wilmington area coaxed Black people from the southern counties to move to the city. The proportion of blacks constituting the city's population rose from 15% in 1950 to over 50% by 1980. The surge of Black migrants to the north sparked white flight, in which middle class whites moved from the city to suburban areas, leading to de facto segregation of Northern Delaware's society. In the 1940s and 1950s, Delaware attempted to integrate its schools, although the last segregated school in the state did not close until 1970. The University of Delaware admitted its first black student in 1948, and local courts ruled that primary schools had to be integrated. Delaware's integration efforts partially inspired the US Supreme Court's decision in Brown v. Board of Education, which found racial segregation in United States public schools to be unconstitutional. The result of the Brown ruling was that Delaware became fully integrated, albeit with time and much effort.

In October 1954, the city of Milford became the scene of one of the country's first pro-segregation boycotts after eleven Black students were enrolled in the previously all-white Milford High School. Mass protests continued in Milford; the school board eventually ceded to the protestors, expelling the Black students. The ensuing unrest, which included cross burnings, rallies, and pro-segregation demonstrations, contributed to desegregation in most of Southern Delaware being delayed for another ten years. Sussex County did not start closing or integrating its segregated schools until 1965, 11 years after the Brown ruling. Throughout the state, integration only encouraged more white flight, and poor economic conditions for the black population led to some violence during the 1960s. Riots broke out in Wilmington in 1967 and again in 1968 in response to the assassination of Martin Luther King Jr, after which the National Guard occupied the city for nine months to prevent further violence.

Since WWII, the state has been generally economically prosperous and enjoyed relatively high per capita income because of its location between major cities like Philadelphia, New York, and Washington, DC. Its population grew rapidly, particularly in the suburbs in the north where New Castle county became an extension of the Philadelphia metropolitan area. Americans, including migrants from Puerto Rico, and immigrants from Latin America flocked to the state. By 1990, only 50% of Delaware's population consisted of natives to the state.

Geography
Delaware is 96 mi long and ranges from 9 to 35 mi across, with a land area of 1982 sqmi and a total area of 2489 sqmi, making it the second-smallest state by either metric in the United States after Rhode Island. Delaware is bounded to the north by Pennsylvania; to the east by the Delaware River, Delaware Bay, New Jersey, and the Atlantic Ocean; and to the west and south by Maryland. Small portions of Delaware are also situated on the eastern side of the Delaware River sharing land boundaries with New Jersey. The state of Delaware, together with the Eastern Shore counties of Maryland and two counties of Virginia, form the Delmarva Peninsula, which stretches down the Mid-Atlantic Coast.

The definition of the northern boundary of the state is unusual. Most of the boundary between Delaware and Pennsylvania was originally defined by an arc extending 12 mi from the cupola of the courthouse in the city of New Castle. This boundary is often referred to as the Twelve-Mile Circle. Although the Twelve-Mile Circle is often claimed to be the only territorial boundary in the U.S. that is a true arc, the Mexican boundary with Texas includes several arcs, and many cities in the South (such as Plains, Georgia) also have circular boundaries.

This border extends all the way east to the low-tide mark on the New Jersey shore, then continues south along the shoreline until it again reaches the 12 mi arc in the south; then the boundary continues in a more conventional way in the middle of the main channel (thalweg) of the Delaware River.

To the west, a portion of the arc extends past the easternmost edge of Maryland. The remaining western border runs slightly east of due south from its intersection with the arc. The Wedge of land between the northwest part of the arc and the Maryland border was claimed by both Delaware and Pennsylvania until 1921, when Delaware's claim was confirmed.

Topography
Delaware is on a level plain, with the lowest mean elevation of any state in the nation. Its highest elevation, located at Ebright Azimuth, near Concord High School, is less than 450 ft above sea level. The northernmost part of the state is part of the Piedmont Plateau with hills and rolling surfaces.

The Atlantic Seaboard fall line approximately follows the Robert Kirkwood Highway between Newark and Wilmington; south of this road is the Atlantic Coastal Plain with flat, sandy, and, in some parts, swampy ground. A ridge about 75 to 80 ft high extends along the western boundary of the state and separates the watersheds that feed Delaware River and Bay to the east and the Chesapeake Bay to the west.

Climate
Since almost all of Delaware is a part of the Atlantic coastal plain, the effects of the ocean moderate its climate. The state lies in the humid subtropical climate (Köppen Cfa) zone. Despite its small size (roughly 100 mi from its northernmost to southernmost points), there is significant variation in mean temperature and amount of snowfall between Sussex County and New Castle County. Moderated by the Atlantic Ocean and Delaware Bay, the southern portion of the state has a milder climate and a longer growing season than the northern portion of the state.

Summers are long, hot, and humid in Delaware, often with intense (but brief) late day thundershowers. Delaware averages 2,300 hrs of sunshine annually (higher than the USA average). Winters are modestly cool to cold in northern Delaware, and cool to mild in southern Delaware. The normal seasonal snowfall ranges from about 20.0 inches in Wilmington to only 10.0 inches in Lewes. In many winters no snow will fall in coastal Delaware. Northern Delaware falls into USDA Garden Zone 7a, while southern and coastal areas fall into USDA zone 7b and 8a. The milder climate in southern Delaware allows for subtropical flora such as the windmill palm, needle palm, and dwarf palmetto.

Delaware's all-time record high of 110 F was recorded at Millsboro on July 21, 1930. The all-time record low of -17 F was also recorded at Millsboro, on January 17, 1893. The hardiness zones are 7B and 8A at the Delaware Beaches.

Environment
The transitional climate of Delaware supports a wide variety of vegetation. In the northern third of the state are found Northeastern coastal forests and mixed oak forests typical of the northeastern United States. In the southern two-thirds of the state are found Middle Atlantic coastal forests. Trap Pond State Park, along with areas in other parts of Sussex County, for example, support the northernmost stands of bald cypress trees in North America.

Environmental management
Delaware provides government subsidy support for the clean-up of property "lightly contaminated" by hazardous waste, the proceeds for which come from a tax on wholesale petroleum sales.

Municipalities
Wilmington is the state's most populous city (70,635) and its economic hub. It is located within commuting distance of both Philadelphia and Baltimore. Dover is the state capital and the second most populous city (38,079).

Counties

 * Kent
 * New Castle
 * Sussex

Cities

 * Delaware City
 * Dover
 * Harrington
 * Lewes
 * Middletown
 * Milford
 * New Castle
 * Newark
 * Rehoboth Beach
 * Seaford
 * Wilmington

Towns

 * Bellefonte
 * Bethany Beach
 * Bethel
 * Blades
 * Bowers
 * Bridgeville
 * Camden
 * Cheswold
 * Clayton
 * Dagsboro
 * Delmar
 * Dewey Beach
 * Ellendale
 * Elsmere
 * Farmington
 * Felton
 * Fenwick Island
 * Frankford
 * Frederica
 * Georgetown
 * Greenwood
 * Hartly
 * Henlopen Acres
 * Houston
 * Kenton
 * Laurel
 * Leipsic
 * Little Creek
 * Magnolia
 * Millsboro
 * Millville
 * Milton
 * Newport
 * Ocean View
 * Odessa
 * Selbyville
 * Slaughter Beach
 * Smyrna
 * South Bethany
 * Townsend
 * Viola
 * Woodside
 * Wyoming

Villages

 * Arden
 * Ardencroft
 * Ardentown

Unincorporated places

 * Bear
 * Brookside
 * Christiana
 * Clarksville
 * Claymont
 * Dover Base Housing
 * Edgemoor
 * Glasgow
 * Greenville
 * Gumboro
 * Harbeson
 * Highland Acres
 * Hockessin
 * Kent Acres
 * Lincoln City
 * Long Neck
 * Marshallton
 * Mount Pleasant
 * North Star
 * Oak Orchard
 * Omar
 * Pennyhill
 * Pike Creek
 * Pike Creek Valley
 * Rising Sun-Lebanon
 * Riverview
 * Rodney Village
 * Roxana
 * Saint Georges
 * Sandtown
 * Stanton
 * Wilmington Manor
 * Wooddale
 * Woodland
 * Woodside East
 * Yorklyn

The table below lists the ten largest municipalities in the state based on the 2020 United States census.

Demographics

The United States Census Bureau determined that the population of Delaware was 989,948 on April 1, 2020, an increase from the 2010 census figure of 897,934.

Delaware's history as a border state has led it to exhibit characteristics of both the Northern and the Southern regions of the United States. Generally, the rural Southern (or "Slower Lower") regions of Delaware below the Chesapeake and Delaware Canal embody a Southern culture, while densely-populated Northern Delaware above the canal—particularly Wilmington, a part of the Philadelphia metropolitan area—has more in common with that of the Northeast and the North. The U.S. Census Bureau designates Delaware as one of the South Atlantic States, but it is commonly associated with the Mid-Atlantic States or northeastern United States by other federal agencies, the media, and some residents.

Delaware is the sixth most densely populated state, with a population density of 442.6 people per square mile, 356.4 per square mile more than the national average, and ranking 45th in population. Delaware is one of five U.S. states (Maine, Vermont, West Virginia, Wyoming) that do not have a single city with a population over 100,000 as of the 2010 census. The center of population of Delaware is in New Castle County, in the town of Townsend.

According to HUD's 2022 Annual Homeless Assessment Report, there were an estimated 2,369 homeless people in Delaware.

Race and ethnicity
According to the 2010 United States census, the racial composition of the state was 68.9% White American (65.3% Non-Hispanic White, 3.6% White Hispanic), 21.4% Black or African American, 0.5% American Indian and Alaska Native, 3.2% Asian American, 0.0% Native Hawaiian and other Pacific Islander, 3.4% some other race, and 2.7% of multiracial origin. People of Hispanic or Latino origin, of any race, made up 8.2% of the population.

The 2022 American Community Survey estimated the state had a racial and ethnic makeup of 60.6% non-Hispanic whites, 23.6% Black or African American, 0.7% American Indian or Alaska Native, 4.2% Asian, 0.1% Pacific Islander, 2.9% multiracial, and 10.1% Hispanic or Latin American of any race.

In the Native American community, the state has a Native American group, called in their own language Lenape, which was influential in the colonial period of the United States and is today headquartered in Cheswold, Kent County, Delaware. A band of the Nanticoke tribe of American Indians today resides in Sussex County and is headquartered in Millsboro, Sussex County, Delaware.

Delaware's population mainly consisted of people from the British Isles, African slaves, Germans and a few remaining Native Americans during the colonial era. Irish, Germans, Italians, Poles, and Russian Jewish immigrants were attracted by the industries in the Wilmington area. In the late 20th century a Puerto Rican community formed in Wilmington. Guatemalan people migrated to Sussex county to work in Delaware's poultry industry. A group of Native Americans in Delaware of mixed ethnicity, the Moors, live in Cheswold. The descendants of the Nanticoke people live around Millsboro. There is also a small numbers of Asians in New Castle county who work as scientific and engineering professionals.

The top countries of origin for Delaware's immigrants in 2018 were Mexico, India, Guatemala, China, and Jamaica.

Birth data
Note: Births in table do not add up because Hispanics are counted both by their ethnicity and by their race, giving a higher overall number.

 * Since 2016, data for births of White Hispanic origin are not collected, but included in one Hispanic group; persons of Hispanic origin may be of any race.

Languages
In 2000, 91% of Delaware residents of age   5 and older spoke only English at home; 5% spoke Spanish. French was the third most spoken language, used by 0.7% of the population, followed by Chinese (0.5%) and German (0.5%). Legislation has been proposed in both the House and the Senate in Delaware to designate English as the official language. Neither bill was passed in the legislature.

Sexual orientation
A 2012 Gallup poll found that Delaware's proportion of lesbian, gay, bisexual, and transgender adults stood at 3.4% of the population. This constitutes a total LGBT adult population estimate of 23,698 people. The number of same-sex couple households in 2010 stood at 2,646. This grew by 41.65% from a decade earlier. On July 1, 2013, same-sex marriage was legalized, and all civil unions were converted into marriages.

Religion
The predominant religion practiced in Delaware is Christianity. A 2014 estimate by the Pew Research Center found that members of Protestant churches accounted for almost half of the population, though the Roman Catholic Church was the largest single denomination in the state. By 2020, the Public Religion Research Institute determined 61% of the population was Christian. In 2022, the Public Religion Research Institute's survey revealed 60% were Christian, followed by Jews (3%), Hindus (1%), and New Agers (1%).

The Association of Religion Data Archives reported in 2010 that the three largest Christian denominational groups in Delaware by number of adherents are the Catholic Church at 182,532 adherents, the United Methodist Church with 53,656 members reported, and non-denominational evangelical Protestants, who numbered 22,973. In 2020, the Association of Religion Data Archives reported the largest Christian denominations were the Catholic Church with 197,094; non-denominational Protestants with 49,392, and United Methodists with 39,959.

The Roman Catholic Diocese of Wilmington and the Episcopal Diocese of Delaware oversee the parishes within their denominations. The A.U.M.P. Church, the oldest African-American denomination in the nation, was founded in Wilmington. It still has a substantial presence in the state. Reflecting new immigrant populations, an Islamic mosque has been built in the Ogletown area, and a Hindu temple in Hockessin.

Delaware is home to an Amish community which resides west of Dover in Kent County, consisting of nine church districts and about 1,650 people. The Amish first settled in Kent County in 1915. In recent years, increasing development has led to the decline in the number of Amish living in the community.

A 2012 survey of religious attitudes in the United States found that 34% of Delaware residents considered themselves "moderately religious", 33% "very religious", and 33% as "non-religious". At the 2014 Pew Research survey, 23% of the population were irreligious; the 2020 Public Religion Research Institute's survey determined 31% of the population were irreligious. In 2022, the same study showed 33% of the population as irreligious.

Affluence
According to a 2020 study by Kiplinger, Delaware had the 17th most millionaires per capita in the United States; altogether, there were 25,937 such individuals. The median income for Delaware households as of 2020 was $64,805.

Agriculture
Delaware's agricultural output consists of poultry, nursery stock, soybeans, dairy products and corn.

Industries
, the state's unemployment rate was 3.7%.

The state's largest employers are:
 * government (State of Delaware, New Castle County)
 * education (University of Delaware, Delaware Technical Community College)
 * banking (Bank of America, M&T Bank, JPMorgan Chase, Citigroup, Deutsche Bank)
 * chemical, pharmaceutical, technology (DuPont de Nemours Inc., AstraZeneca, Syngenta, Agilent Technologies)
 * healthcare (ChristianaCare (Christiana Hospital), Bayhealth Medical Center, Nemours Children's Hospital, Delaware)
 * farming, specifically chicken farming in Sussex County (Perdue Farms, Mountaire Farms, Allen Family Foods)
 * retail (Walmart, Walgreens, Acme Markets)

Industrial decline
Since the mid-2000s, Delaware has seen the departure of the state's automotive manufacturing industry (General Motors Wilmington Assembly and Chrysler Newark Assembly), the corporate buyout of a major bank holding company (MBNA), the departure of the state's steel industry (Evraz Claymont Steel), the bankruptcy of a fiber mill (National Vulcanized Fiber), and the diminishing presence of AstraZeneca in Wilmington.

In late 2015, DuPont announced that 1,700 employees, nearly a third of its footprint in Delaware, would be laid off in early 2016. The merger of E.I. du Pont de Nemours & Co. and Dow Chemical Company into DowDuPont took place on September 1, 2017.

Incorporation in Delaware
More than half of all U.S. publicly traded companies, and 63% of the Fortune 500, are incorporated in Delaware. The state's attractiveness as a corporate haven is largely because of its business-friendly corporation law. Franchise taxes on Delaware corporations supply about a fifth of the state's revenue. Although "USA (Delaware)" ranked as the world's most opaque jurisdiction on the Tax Justice Network's 2009 Financial Secrecy Index, the same group's 2011 Index ranks the U.S. fifth and does not specify Delaware. In Delaware, there are more than a million registered corporations, meaning there are more corporations than people.

Food and drink
Title 4, chapter 7 of the Delaware Code stipulates that alcoholic liquor be sold only in specifically licensed establishments, and only between 9:00   a.m. and 1:00    a.m. Until 2003, Delaware was among the several states enforcing blue laws and banned the sale of liquor on Sunday.

Newspapers
Two daily newspapers are based in Delaware, the Delaware State News, based in Dover and covering the two southern counties, and The News Journal covering Wilmington and northern Delaware. The state is also served by several weekly, monthly and online publications.

Television
No standalone television stations are based solely in Delaware. The northern part of the state is served by network stations in Philadelphia and the southern part by network stations in Salisbury, Maryland. Philadelphia's ABC affiliate, WPVI-TV, maintains a news bureau in downtown Wilmington. Salisbury's CBS affiliate, WBOC-TV, maintains bureaus in Dover and Milton. Three Philadelphia-market stations—PBS member WHYY-TV, Ion affiliate WPPX, and MeTV affiliate WDPN-TV—all have Wilmington as their city of license, but maintain transmitters at the market antenna farm in Roxborough, Philadelphia and do not produce any Delaware-centric programming.

Radio
There are a numerous radio stations licensed in Delaware. WDDE 91.1 FM, WDEL 1150AM, WHGE-LP 95.3 FM, WILM 1450 AM, WVCW 99.5, WMPH 91.7 FM, WSTW 93.7 FM, WTMC 1380 AM and WWTX 1290AM are licensed from Wilmington. WRDX 92.9 FM is licensed from Smyrna. WDOV 1410AM, WDSD 94.7 FM and WRTX 91.7 FM are licensed from Dover.

Tourism
Delaware is home to First State National Historical Park, a National Park Service unit composed of historic sites across the state including the New Castle Court House, Green, and Sheriff's House, Dover Green, Beaver Valley, Fort Christina, Old Swedes' Church, John Dickinson Plantation, and the Ryves Holt House. Delaware has several museums, wildlife refuges, parks, houses, lighthouses, and other historic places.

Rehoboth Beach, together with the towns of Lewes, Dewey Beach, Bethany Beach, South Bethany, and Fenwick Island, comprise Delaware's beach resorts. Rehoboth Beach often bills itself as "The Nation's Summer Capital" because it is a frequent summer vacation destination for Washington, D.C., residents as well as visitors from Maryland, Virginia, and in lesser numbers, Pennsylvania. Vacationers are drawn for many reasons, including the town's charm, artistic appeal, nightlife, and tax-free shopping. According to SeaGrant Delaware, the Delaware beaches generate $6.9   billion annually and over $711    million in tax revenue.

Delaware is home to several festivals, fairs, and events. Some of the more notable festivals are the Riverfest held in Seaford, the World Championship Punkin Chunkin formerly held at various locations throughout the state since 1986, the Rehoboth Beach Chocolate Festival, the Bethany Beach Jazz Funeral to mark the end of summer, the Apple Scrapple Festival held in Bridgeville, the Clifford Brown Jazz Festival in Wilmington, the Rehoboth Beach Jazz Festival, the Sea Witch Halloween Festival and Parade in Rehoboth Beach, the Rehoboth Beach Independent Film Festival, the Nanticoke Indian Pow Wow in Oak Orchard, Firefly Music Festival, and the Return Day Parade held after every election in Georgetown.

In 2015, tourism in Delaware generated $3.1   billion, which makes up five percent of the state's GDP. Delaware saw 8.5   million visitors in 2015, with the tourism industry employing 41,730 people, making it the 4th largest private employer in the state. Major origin markets for Delaware tourists include Philadelphia, Baltimore, New York City, Washington, D.C., and Harrisburg, with 97% of tourists arriving to the state by car and 75% of tourists coming from a distance of 200 mi or less.

Delaware is also home to two large sporting venues. Dover Motor Speedway is a race track in Dover, and Frawley Stadium in Wilmington is the home of the Wilmington Blue Rocks, a Minor League Baseball team that is currently affiliated with the Washington Nationals.

Education
In the early 1920s, Pierre S. du Pont served as president of the state board of education. At the time, state law prohibited money raised from white taxpayers from being used to support the state's schools for black children. Appalled by the condition of the black schools, du Pont donated four million dollars to construct 86 new school buildings.

Delaware was the origin of Belton v. Gebhart (1952), one of the four cases which were combined into Brown v. Board of Education, the Supreme Court of the United States decision that led to the end of officially segregated public schools. Significantly, Belton was the only case in which the state court found for the plaintiffs, thereby ruling that segregation is unconstitutional.

Unlike many states, Delaware's educational system is centralized in a state Superintendent of Education, with local school boards retaining control over taxation and some curriculum decisions. This centralized system, combined with the small size of the state, likely contributed to Delaware becoming the first state, after completion of a three-year, $30   million program ending in 1999, to wire every K-12 classroom in the state to the Internet.

, the Delaware Department of Education had authorized the founding of 25 charter schools in the state, one of them being all-girls.

All teachers in the State's public school districts are unionized. , none of the State's charter schools are members of a teachers union. One of the State's teachers' unions is Delaware State Education Association (DSEA).

Colleges and universities

 * Delaware College of Art and Design
 * Delaware State University
 * Delaware Technical & Community College
 * Goldey-Beacom College
 * University of Delaware—Ranked 63rd in the U.S. and in top 201–250 in the world (Times Higher Education World University Rankings 2018)
 * Widener University School of Law
 * Wilmington University

Transportation

The transportation system in Delaware is under the governance and supervision of the Delaware Department of Transportation (DelDOT). Funding for DelDOT projects is drawn, in part, from the Delaware Transportation Trust Fund, established in 1987 to help stabilize transportation funding; the availability of the Trust led to a gradual separation of DelDOT operations from other Delaware state operations. DelDOT manages programs such as a Delaware Adopt-a-Highway program, major road route snow removal, traffic control infrastructure (signs and signals), toll road management, Delaware Division of Motor Vehicles, the Delaware Transit Corporation (branded as "DART First State", the state government public transportation organization), and others.

In 2009, DelDOT maintained 13,507 lane-miles, totaling 89 percent of the state's public roadway system, the rest being under the supervision of individual municipalities. This far exceeds the national average (20 percent) for state department of transportation maintenance responsibility.

Roads
One major branch of the U.S. Interstate Highway System, Interstate   95 (I-95), crosses Delaware southwest-to-northeast across New Castle County. Two Auxiliary Interstate Highway routes are also located in the state. Interstate 495 (I-495) is an eastern bypass of Wilmington. Interstate 295 (I-295) is a bypass of Philadelphia which begins south of Wilmington. In addition to Interstate highways, there are six U.S. highways that serve Delaware: U.S.   9, U.S.    13, U.S.    40, U.S.    113, U.S.    202, and U.S.    301. There are also several state highways that cross the state of Delaware; a few of them include DE   1, DE    9, and DE    404. U.S.   13 and DE    1 are primary north–south highways connecting Wilmington and Pennsylvania with Maryland, with DE    1 serving as the main route between Wilmington and the Delaware beaches. DE   9 is a north–south highway connecting Dover and Wilmington via a scenic route along the Delaware Bay. U.S.   40 is a primary east–west route, connecting Maryland with New Jersey. DE   404 is another primary east–west highway connecting the Chesapeake Bay Bridge in Maryland with the Delaware beaches. The state also operates three toll highways, the Delaware Turnpike, which is I-95, between Maryland and New Castle; the Korean War Veterans Memorial Highway, which is DE   1, between Wilmington and Dover; and the U.S. 301 toll road between the Maryland border and DE    1 in New Castle County.

A bicycle route, Delaware Bicycle Route 1, spans the north–south length of the state from the Maryland border in Fenwick Island to the Pennsylvania border north of Montchanin. It is the first of several signed bike routes planned in Delaware.

Delaware has about 875 bridges, 95 percent of which are under the supervision of DelDOT. About 30 percent of all Delaware bridges were built before 1950, and about 60 percent of the number are included in the National Bridge Inventory. Some bridges not under DelDOT supervision includes the four bridges on the Chesapeake and Delaware Canal, which are under the jurisdiction of the U.S. Army Corps of Engineers, and the Delaware Memorial Bridge, which is under the bi-state Delaware River and Bay Authority.

It has been noted that the tar and chip composition of secondary roads in Sussex County makes them more prone to deterioration than are the asphalt roadways in almost the rest of the state. Among these roads, Sussex (county road) 236 is among the most problematic.

Ferries
Three ferries operate in the state of Delaware:
 * Cape May–Lewes Ferry crosses the mouth of Delaware Bay between Lewes, Delaware and Cape May, New Jersey.
 * Woodland Ferry (a cable ferry) crosses the Nanticoke River southwest of Seaford.
 * Forts Ferry Crossing connects Delaware City with Fort Delaware and Fort Mott, New Jersey.

Rail and bus
Amtrak has two stations in Delaware along the Northeast Corridor; the relatively quiet Newark Rail Station in Newark, and the busier Wilmington Station in Wilmington. The Northeast Corridor is also served by SEPTA's Wilmington/Newark Line, part of SEPTA Regional Rail, which serves Claymont, Wilmington, Churchmans Crossing, and Newark.

Two Class I railroads, Norfolk Southern and CSX, provide freight rail service in northern New Castle County. Norfolk Southern provides freight service along the Northeast Corridor and to industrial areas in Edgemoor, New Castle, and Delaware City. CSX's Philadelphia Subdivision passes through northern New Castle County parallel to the Amtrak Northeast Corridor. Multiple short-line railroads provide freight service in Delaware. The Delmarva Central Railroad operates the most trackage of the short-line railroads, running from an interchange with Norfolk Southern in Porter south through Dover, Harrington, and Seaford to Delmar, with another line running from Harrington to Frankford and branches from Ellendale to Milton and from Georgetown to Gravel Hill. The Delmarva Central Railroad connects with the Maryland and Delaware Railroad, which serves local customers in Sussex County. CSX connects with the freight/heritage operation, the Wilmington and Western Railroad, based in Wilmington and the East Penn Railroad, which operates a line from Wilmington to Coatesville, Pennsylvania.

The last north–south passenger trains through the main part of Delaware was the Pennsylvania Railroad's local Wilmington-Delmar train in 1965. This was a successor to the Del-Mar-Va Express and Cavalier, which had run from Philadelphia through the state's interior, to the end of the Delmarva Peninsula until the mid-1950s.

The DART First State public transportation system was named "Most Outstanding Public Transportation System" in 2003 by the American Public Transportation Association. Coverage of the system is broad within northern New Castle County with close association to major highways in Kent and Sussex counties. The system includes bus, subsidized passenger rail operated by Philadelphia transit agency SEPTA, and subsidized taxi and paratransit modes. The paratransit system, consisting of a statewide door-to-door bus service for the elderly and disabled, has been described by a Delaware state report as "the most generous paratransit system in the United States". , fees for the paratransit service have not changed since 1988.

Air
, Delaware is served exclusively by Avelo Airlines out of Wilmington Airport, launching five routes to Florida on February 1. This put an end to an eight-month period during which Delaware had no scheduled air service, one of several since 1991. Various airlines had served Wilmington Airport, the latest departure being Frontier Airlines in June 2022.

Delaware is centrally situated in the Northeast megalopolis region of cities along I-95. Therefore, Delaware commercial airline passengers most frequently use Philadelphia International Airport (PHL), Baltimore-Washington International Thurgood Marshall Airport (BWI) and Washington Dulles International Airport (IAD) for domestic and international transit. Residents of Sussex County will also use Wicomico Regional Airport (SBY), as it is located less than 10 mi from the Delaware border. Atlantic City International Airport (ACY), Newark Liberty International Airport (EWR), and Ronald Reagan Washington National Airport (DCA) are also within a 100 mi radius of New Castle County.

Other general aviation airports in Delaware include Summit Airport near Middletown, Delaware Airpark near Cheswold, and Delaware Coastal Airport near Georgetown.

Dover Air Force Base, one of the largest in the country, is home to the 436th Airlift Wing and the 512th Airlift Wing. In addition to its other responsibilities in the Air Mobility Command, it serves as the entry point and mortuary for U.S. military personnel (and some civilians) who die overseas.

Law and government
Delaware's fourth and current constitution, adopted in 1897, provides for executive, judicial and legislative branches.

Legislative branch
The Delaware General Assembly consists of a House of Representatives with 41 members and a Senate with 21 members. It sits in Dover, the state capital. Representatives are elected to two-year terms, while senators are elected to four-year terms. The Senate confirms judicial and other nominees appointed by the governor.

Delaware's U.S. Senators are Tom Carper (Democrat) and Chris Coons (Democrat). Delaware's single U.S. Representative is Lisa Blunt Rochester (Democrat).

Judicial branch
The Delaware Constitution establishes a number of courts:
 * The Delaware Supreme Court is the state's highest court.
 * The Delaware Superior Court is the state's trial court of general jurisdiction.
 * The Delaware Court of Chancery deals primarily in corporate disputes.
 * The Family Court handles domestic and custody matters.
 * The Delaware Court of Common Pleas has jurisdiction over a limited class of civil and criminal matters.

Minor non-constitutional courts include the Justice of the Peace Courts and Aldermen's Courts.

Significantly, Delaware has one of the few remaining Courts of Chancery in the nation, which has jurisdiction over equity cases, the vast majority of which are corporate disputes, many relating to mergers and acquisitions. The Court of Chancery and the Delaware Supreme Court have developed a worldwide reputation for rendering concise opinions concerning corporate law which generally (but not always) grant broad discretion to corporate boards of directors and officers. In addition, the Delaware General Corporation Law, which forms the basis of the Courts' opinions, is widely regarded as giving great flexibility to corporations to manage their affairs. For these reasons, Delaware is considered to have the most business-friendly legal system in the United States; therefore a great number of companies are incorporated in Delaware, including 60% of the companies listed on the New York Stock Exchange.

Delaware was the last U.S. state to use judicial corporal punishment, in 1952.

Executive branch
The executive branch is headed by the Governor of Delaware. The current governor is John Carney (Democrat), who took office January 17, 2017. The lieutenant governor is Bethany Hall-Long. The governor presents a "State of the State" speech to a joint session of the Delaware legislature annually.

The executive branch also consists of the Attorney General of Delaware currently held by Kathy Jennings, the State Treasurer currently held by Colleen Davis, the Auditor of Accounts currently held by Lydia York and the Insurance Commissioner currently held by Trinidad Navarro.

Counties
Delaware is subdivided into three counties; from north to south they are New Castle, Kent and Sussex. This is the fewest among all states. Each county elects its own legislative body (known in New Castle and Sussex counties as County Council, and in Kent County as Levy Court), which deal primarily in zoning and development issues. Most functions which are handled on a county-by-county basis in other states—such as court and law enforcement—have been centralized in Delaware, leading to a significant concentration of power in the Delaware state government. The counties were historically divided into hundreds, which were used as tax reporting and voting districts until the 1960s, but now serve no administrative role, their only current official legal use being in real estate title descriptions.

Politics
The Democratic Party holds a plurality of registrations in Delaware. Currently, Democrats hold all positions of authority in Delaware, as well as majorities in the state Senate and House. The Democrats have held the governorship since 1993, having won the last seven gubernatorial elections. Democrats presently hold all the nine statewide elected offices, while the Republicans last won any statewide offices in 2014, State Auditor and State Treasurer.

During the First and Second Party Systems, Delaware was a stronghold for the Federalist and Whig Parties, respectively. After a relatively brief adherence to the Democratic Solid South following the US Civil War, Delaware became a Republican-leaning state from 1896 through 1948, voting for losing Republicans Charles Evans Hughes in 1916, Herbert Hoover in 1932, and Thomas Dewey in 1948.

During the second half of the 20th century, Delaware was a bellwether state, voting for the winner of every presidential election from 1952 through 1996. Delaware's bellwether status came to an end when Delaware voted for Al Gore in 2000 by 13%. Subsequent elections have continued to demonstrate Delaware's current strong Democratic lean: John Kerry carried the First State by 8% in 2004; Barack Obama carried it by 25% and by 19% in his two elections of 2008 and 2012; and Hillary Clinton carried it by 11% as she lost the Electoral College in 2016. In 2020, Delaware native (and Barack Obama's former vice president and running mate) Joe Biden headed the Democratic ticket; he carried his home state by just shy of 19% en route to a national 4.5% win.

The dominant factor in Delaware's political shift has been the strong Democratic trend in heavily urbanized New Castle County, home to 55% of Delaware's population. New Castle County has not voted Republican in a presidential election since 1988, and has given Democrats over 60% of its vote in every election from 2004 on. In 1992, 2000, 2004, and 2016, the Republican presidential candidate carried both Kent and Sussex but lost by double digits each time in New Castle County, which was a large enough margin to tip the state to the Democrats. New Castle County also elects a substantial majority of the state legislature; 27 of the 41 state house districts and 14 of the 21 state senate districts are based in New Castle County.

In a 2020 study, Delaware was ranked as the 18th hardest state for citizens to vote in.

Freedom of information
Each of the 50 states of the United States has passed some form of freedom of information legislation, which provides a mechanism for the general public to request information of the government. In 2011 Delaware passed legislation placing a 15 business day time limit on addressing freedom-of-information requests, to either produce information or an explanation of why such information would take longer than this time to produce. A bill aimed at restricting Freedom of Information Act requests, Senate Bill 155, was discussed in committee.

Taxation
Tax is collected by the Delaware Division of Revenue.

Delaware has six different income tax brackets, ranging from 2.2% to 5.95%. The state does not assess sales tax on consumers. The state does, however, impose a tax on the gross receipts of most businesses. Business and occupational license tax rates range from 0.096% to 1.92%, depending on the category of business activity.

Delaware does not assess a state-level tax on real or personal property. Real estate is subject to county property taxes, school district property taxes, vocational school district taxes, and, if located within an incorporated area, municipal property taxes.

Gambling provides significant revenue to the state. For instance, the casino at Delaware Park Racetrack provided more than $100   million to the state in 2010.

In June 2018, Delaware became the first U.S. state to legalize sports betting following the Supreme Court ruling to overturn the Professional and Amateur Sports Protection Act of 1992 (PASPA).

Sports

 * Professional teams

As Delaware has no franchises in the major American professional sports leagues, many Delawareans follow either Philadelphia or Baltimore teams. In the WNBA, the Washington Mystics enjoy a major following due to the presence of Wilmington native and University of Delaware product Elena Delle Donne. The University of Delaware's football team has a large following throughout the state, with the Delaware State University and Wesley College teams also enjoying a smaller degree of support.

Delaware is home to Dover Motor Speedway and Bally's Dover. Dover Motor Speedway, also known as the Monster Mile, is one of only 10 tracks in the nation to have hosted 100 or more NASCAR Cup Series races. Bally's Dover is a popular harness racing facility. It is the only co-located horse- and car-racing facility in the nation, with the Bally's Dover track located inside the Dover Motor Speedway track.

Delaware is represented in rugby by the Delaware Black Foxes, a 2015 expansion club.

Delaware has been home to professional wrestling outfit Combat Zone Wrestling (CZW). CZW has been affiliated with the annual Tournament of Death and ECWA with its annual Super   8 Tournament.

Delaware's official state sport is bicycling.

Sister State
Delaware has had a foreign sister state in Japan, named Miyagi Prefecture. These two have shared relations since 1997, and have had exchange programs available for students that were briefly paused in wake of the earthquake and the tsunami that ensued in the prefecture during March 2011.

Delawareans
Prominent Delawareans include the du Pont family of politicians and businesspersons, and the 46th and current president of the United States Joe Biden, whose family moved to Delaware during his childhood, and who later represented Delaware for 36 years in the United States Senate before becoming the 47th vice president of the United States.

General

 * Delaware Tourism homepage
 * Delaware Map Data
 * Energy & Environmental Data for Delaware
 * USGS real-time, geographic, and other scientific resources of Delaware
 * U.S. Census Bureau
 * Delaware State Facts from USDA
 * 2000 Census of Population and Housing for Delaware, U.S. Census Bureau
 * Delaware State Databases—Annotated list of searchable databases produced by Delaware state agencies and compiled by the Government Documents Roundtable of the American Library Association
 * 2000 Census of Population and Housing for Delaware, U.S. Census Bureau
 * Delaware State Databases—Annotated list of searchable databases produced by Delaware state agencies and compiled by the Government Documents Roundtable of the American Library Association
 * Delaware State Databases—Annotated list of searchable databases produced by Delaware state agencies and compiled by the Government Documents Roundtable of the American Library Association
 * Delaware State Databases—Annotated list of searchable databases produced by Delaware state agencies and compiled by the Government Documents Roundtable of the American Library Association

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Dictionary

A dictionary is a listing of lexemes from the lexicon of one or more specific languages, often arranged alphabetically (or by consonantal root for Semitic languages or radical and stroke for logographic languages), which may include information on definitions, usage, etymologies, pronunciations, translation, etc. It is a lexicographical reference that shows inter-relationships among the data.

A broad distinction is made between general and specialized dictionaries. Specialized dictionaries include words in specialist fields, rather than a comprehensive range of words in the language. Lexical items that describe concepts in specific fields are usually called terms instead of words, although there is no consensus whether lexicology and terminology are two different fields of study. In theory, general dictionaries are supposed to be semasiological, mapping word to definition, while specialized dictionaries are supposed to be onomasiological, first identifying concepts and then establishing the terms used to designate them. In practice, the two approaches are used for both types. There are other types of dictionaries that do not fit neatly into the above distinction, for instance bilingual (translation) dictionaries, dictionaries of synonyms (thesauri), and rhyming dictionaries. The word dictionary (unqualified) is usually understood to refer to a general purpose monolingual dictionary.

There is also a contrast between prescriptive or descriptive dictionaries; the former reflect what is seen as correct use of the language while the latter reflect recorded actual use. Stylistic indications (e.g. "informal" or "vulgar") in many modern dictionaries are also considered by some to be less than objectively descriptive.

The first recorded dictionaries date back to Sumerian times around 2300 BCE, in the form of bilingual dictionaries, and the oldest surviving monolingual dictionaries are Chinese dictionaries c. 3rd century BCE. The first purely English alphabetical dictionary was A Table Alphabeticall, written in 1604, and monolingual dictionaries in other languages also began appearing in Europe at around this time. The systematic study of dictionaries as objects of scientific interest arose as a 20th-century enterprise, called lexicography, and largely initiated by Ladislav Zgusta. The birth of the new discipline was not without controversy, with the practical dictionary-makers being sometimes accused by others of having an "astonishing" lack of method and critical-self reflection.

History

The oldest known dictionaries were cuneiform tablets with bilingual Sumerian–Akkadian wordlists, discovered in Ebla (modern Syria) and dated to roughly 2300 BCE, the time of the Akkadian Empire. The early 2nd millennium BCE Urra=hubullu glossary is the canonical Babylonian version of such bilingual Sumerian wordlists. A Chinese dictionary, the c. 3rd century BCE Erya, is the earliest surviving monolingual dictionary; and some sources cite the Shizhoupian (probably compiled sometime between 700 BCE to 200 BCE, possibly earlier) as a "dictionary", although modern scholarship considers it a calligraphic compendium of Chinese characters from Zhou dynasty bronzes. Philitas of Cos (fl. 4th century BCE) wrote a pioneering vocabulary Disorderly Words (Ἄτακτοι γλῶσσαι, ) which explained the meanings of rare Homeric and other literary words, words from local dialects, and technical terms. Apollonius the Sophist (fl. 1st century CE) wrote the oldest surviving Homeric lexicon. The first Sanskrit dictionary, the Amarakośa, was written by Amarasimha c. 4th century CE. Written in verse, it listed around 10,000 words. According to the Nihon Shoki, the first Japanese dictionary was the long-lost 682 CE Niina glossary of Chinese characters. Al-Khalil ibn Ahmad al-Farahidi's 8th century Kitab al-'Ayn is considered the first dictionary of Arabic. The oldest existing Japanese dictionary, the c. 835 CE Tenrei Banshō Meigi, was also a glossary of written Chinese. In Frahang-i Pahlavig, Aramaic heterograms are listed together with their translation in the Middle Persian language and phonetic transcription in the Pazend alphabet. A 9th-century CE Irish dictionary, Sanas Cormaic, contained etymologies and explanations of over 1,400 Irish words. In the 12th century, The Karakhanid-Turkic scholar Mahmud Kashgari finished his work "Divan-u Lügat'it Türk", a dictionary about the Turkic dialects, but especially Karakhanid Turkic. His work contains about 7500 to 8000 words and it was written to teach non Turkic Muslims, especially the Abbasid Arabs, the Turkic language. Al-Zamakhshari wrote a small Arabic dictionary called "Muḳaddimetü'l-edeb" for the Turkic-Khwarazm ruler Atsiz. In the 14th century, the Codex Cumanicus was finished and it served as a dictionary about the Cuman-Turkic language. While in Mamluk Egypt, Ebû Hayyân el-Endelüsî finished his work "Kitâbü'l-İdrâk li-lisâni'l-Etrâk", a dictionary about the Kipchak and Turcoman languages spoken in Egypt and the Levant. A dictionary called "Bahşayiş Lügati", which is written in old Anatolian Turkish, served also as a dictionary between Oghuz Turkish, Arabic and Persian. But it is not clear who wrote the dictionary or in which century exactly it was published. It was written in old Anatolian Turkish from the Seljuk period and not the late medieval Ottoman period. In India around 1320, Amir Khusro compiled the Khaliq-e-bari, which mainly dealt with Hindustani and Persian words.

Arabic dictionaries were compiled between the 8th and 14th centuries, organizing words in rhyme order (by the last syllable), by alphabetical order of the radicals, or according to the alphabetical order of the first letter (the system used in modern European language dictionaries). The modern system was mainly used in specialist dictionaries, such as those of terms from the Qur'an and hadith, while most general use dictionaries, such as the Lisan al-`Arab (13th century, still the best-known large-scale dictionary of Arabic) and al-Qamus al-Muhit (14th century) listed words in the alphabetical order of the radicals. The Qamus al-Muhit is the first handy dictionary in Arabic, which includes only words and their definitions, eliminating the supporting examples used in such dictionaries as the Lisan and the Oxford English Dictionary.

In medieval Europe, glossaries with equivalents for Latin words in vernacular or simpler Latin were in use (e.g. the Leiden Glossary). The Catholicon (1287) by Johannes Balbus, a large grammatical work with an alphabetical lexicon, was widely adopted. It served as the basis for several bilingual dictionaries and was one of the earliest books (in 1460) to be printed. In 1502 Ambrogio Calepino's Dictionarium was published, originally a monolingual Latin dictionary, which over the course of the 16th century was enlarged to become a multilingual glossary. In 1532 Robert Estienne published the Thesaurus linguae latinae and in 1572 his son Henri Estienne published the Thesaurus linguae graecae, which served up to the 19th century as the basis of Greek lexicography. The first monolingual Spanish dictionary written was Sebastián Covarrubias's Tesoro de la lengua castellana o española, published in 1611 in Madrid, Spain. In 1612 the first edition of the Vocabolario degli Accademici della Crusca, for Italian, was published. It served as the model for similar works in French and English. In 1690 in Rotterdam was published, posthumously, the Dictionnaire Universel by Antoine Furetière for French. In 1694 appeared the first edition of the Dictionnaire de l'Académie française (still published, with the ninth edition not complete ). Between 1712 and 1721 was published the Vocabulario portughez e latino written by Raphael Bluteau. The Royal Spanish Academy published the first edition of the Diccionario de la lengua española (still published, with a new edition about every decade) in 1780; their Diccionario de Autoridades, which included quotes taken from literary works, was published in 1726. The Totius Latinitatis lexicon by Egidio Forcellini was firstly published in 1777; it has formed the basis of all similar works that have since been published.

The first edition of A Greek-English Lexicon by Henry George Liddell and Robert Scott appeared in 1843; this work remained the basic dictionary of Greek until the end of the 20th century. And in 1858 was published the first volume of the Deutsches Wörterbuch by the Brothers Grimm; the work was completed in 1961. Between 1861 and 1874 was published the Dizionario della lingua italiana by Niccolò Tommaseo. Between 1862 and 1874 was published the six volumes of A magyar nyelv szótára (Dictionary of Hungarian Language) by Gergely Czuczor and János Fogarasi. Émile Littré published the Dictionnaire de la langue française between 1863 and 1872. In the same year 1863 appeared the first volume of the Woordenboek der Nederlandsche Taal which was completed in 1998. Also in 1863 Vladimir Ivanovich Dahl published the Explanatory Dictionary of the Living Great Russian Language. The Duden dictionary dates back to 1880, and is currently the prescriptive source for the spelling of German. The decision to start work on the Svenska Akademiens ordbok was taken in 1787.

English dictionaries in Britain
The earliest dictionaries in the English language were glossaries of French, Spanish or Latin words along with their definitions in English. The word "dictionary" was invented by an Englishman called John of Garland in 1220 – he had written a book Dictionarius to help with Latin "diction". An early non-alphabetical list of 8000 English words was the Elementarie, created by Richard Mulcaster in 1582.

The first purely English alphabetical dictionary was A Table Alphabeticall, written by English schoolteacher Robert Cawdrey in 1604. The only surviving copy is found at the Bodleian Library in Oxford. This dictionary, and the many imitators which followed it, was seen as unreliable and nowhere near definitive. Philip Stanhope, 4th Earl of Chesterfield was still lamenting in 1754, 150 years after Cawdrey's publication, that it is "a sort of disgrace to our nation, that hitherto we have had no… standard of our language; our dictionaries at present being more properly what our neighbors the Dutch and the Germans call theirs, word-books, than dictionaries in the superior sense of that title."

In 1616, John Bullokar described the history of the dictionary with his "English Expositor". Glossographia by Thomas Blount, published in 1656, contains more than 10,000 words along with their etymologies or histories. Edward Phillips wrote another dictionary in 1658, entitled "The New World of English Words: Or a General Dictionary" which boldly plagiarized Blount's work, and the two criticised each other. This created more interest in the dictionaries. John Wilkins' 1668 essay on philosophical language contains a list of 11,500 words with careful distinctions, compiled by William Lloyd. Elisha Coles published his "English Dictionary" in 1676.

It was not until Samuel Johnson's A Dictionary of the English Language (1755) that a more reliable English dictionary was produced. Many people today mistakenly believe that Johnson wrote the first English dictionary: a testimony to this legacy. By this stage, dictionaries had evolved to contain textual references for most words, and were arranged alphabetically, rather than by topic (a previously popular form of arrangement, which meant all animals would be grouped together, etc.). Johnson's masterwork could be judged as the first to bring all these elements together, creating the first "modern" dictionary.

Johnson's dictionary remained the English-language standard for over 150 years, until the Oxford University Press began writing and releasing the Oxford English Dictionary in short fascicles from 1884 onwards. It took nearly 50 years to complete this huge work, and they finally released the complete OED in twelve volumes in 1928. One of the main contributors to this modern dictionary was an ex-army surgeon, William Chester Minor, a convicted murderer who was confined to an asylum for the criminally insane.

The OED remains the most comprehensive and trusted English language dictionary to this day, with revisions and updates added by a dedicated team every three months.

American English dictionaries
In 1806, American Noah Webster published his first dictionary, A Compendious Dictionary of the English Language. In 1807 Webster began compiling an expanded and fully comprehensive dictionary, An American Dictionary of the English Language; it took twenty-seven years to complete. To evaluate the etymology of words, Webster learned twenty-six languages, including Old English (Anglo-Saxon), German, Greek, Latin, Italian, Spanish, French, Hebrew, Arabic, and Sanskrit.

Webster completed his dictionary during his year abroad in 1825 in Paris, France, and at the University of Cambridge. His book contained seventy thousand words, of which twelve thousand had never appeared in a published dictionary before. As a spelling reformer, Webster believed that English spelling rules were unnecessarily complex, so his dictionary introduced spellings that became American English, replacing "colour" with "color", substituting "wagon" for "waggon", and printing "center" instead of "centre". He also added American words, like "skunk" and "squash", which did not appear in British dictionaries. At the age of seventy, Webster published his dictionary in 1828; it sold 2500 copies. In 1840, the second edition was published in two volumes. Webster's dictionary was acquired by G & C Merriam Co. in 1843, after his death, and has since been published in many revised editions. Merriam-Webster was acquired by Encyclopedia Britannica in 1964.

Controversy over the lack of usage advice in the 1961 Webster's Third New International Dictionary spurred publication of the 1969 The American Heritage Dictionary of the English Language, the first dictionary to use corpus linguistics.

Types
In a general dictionary, each word may have multiple meanings. Some dictionaries include each separate meaning in the order of most common usage while others list definitions in historical order, with the oldest usage first.

In many languages, words can appear in many different forms, but only the undeclined or unconjugated form appears as the headword in most dictionaries. Dictionaries are most commonly found in the form of a book, but some newer dictionaries, like StarDict and the New Oxford American Dictionary are dictionary software running on PDAs or computers. There are also many online dictionaries accessible via the Internet.

Specialized dictionaries
According to the Manual of Specialized Lexicographies, a specialized dictionary, also referred to as a technical dictionary, is a dictionary that focuses upon a specific subject field, as opposed to a dictionary that comprehensively contains words from the lexicon of a specific language or languages. Following the description in The Bilingual LSP Dictionary, lexicographers categorize specialized dictionaries into three types: A multi-field dictionary broadly covers several subject fields (e.g. a business dictionary), a single-field dictionary narrowly covers one particular subject field (e.g. law), and a sub-field dictionary covers a more specialized field (e.g. constitutional law). For example, the 23-language Inter-Active Terminology for Europe is a multi-field dictionary, the American National Biography is a single-field, and the African American National Biography Project is a sub-field dictionary. In terms of the coverage distinction between "minimizing dictionaries" and "maximizing dictionaries", multi-field dictionaries tend to minimize coverage across subject fields (for instance, Oxford Dictionary of World Religions and Yadgar Dictionary of Computer and Internet Terms) whereas single-field and sub-field dictionaries tend to maximize coverage within a limited subject field (The Oxford Dictionary of English Etymology).

Another variant is the glossary, an alphabetical list of defined terms in a specialized field, such as medicine (medical dictionary).

Defining dictionaries
The simplest dictionary, a defining dictionary, provides a core glossary of the simplest meanings of the simplest concepts. From these, other concepts can be explained and defined, in particular for those who are first learning a language. In English, the commercial defining dictionaries typically include only one or two meanings of under 2000 words. With these, the rest of English, and even the 4000 most common English idioms and metaphors, can be defined.

Prescriptive vs. descriptive
Lexicographers apply two basic philosophies to the defining of words: prescriptive or descriptive. Noah Webster, intent on forging a distinct identity for the American language, altered spellings and accentuated differences in meaning and pronunciation of some words. This is why American English now uses the spelling color while the rest of the English-speaking world prefers colour. (Similarly, British English subsequently underwent a few spelling changes that did not affect American English; see further at American and British English spelling differences.)

Large 20th-century dictionaries such as the Oxford English Dictionary (OED) and Webster's Third are descriptive, and attempt to describe the actual use of words. Most dictionaries of English now apply the descriptive method to a word's definition, and then, outside of the definition itself, provide information alerting readers to attitudes which may influence their choices on words often considered vulgar, offensive, erroneous, or easily confused. Merriam-Webster is subtle, only adding italicized notations such as, sometimes offensive or stand (nonstandard). American Heritage goes further, discussing issues separately in numerous "usage notes." Encarta provides similar notes, but is more prescriptive, offering warnings and admonitions against the use of certain words considered by many to be offensive or illiterate, such as, "an offensive term for..." or "a taboo term meaning...".

Because of the widespread use of dictionaries in schools, and their acceptance by many as language authorities, their treatment of the language does affect usage to some degree, with even the most descriptive dictionaries providing conservative continuity. In the long run, however, the meanings of words in English are primarily determined by usage, and the language is being changed and created every day. As Jorge Luis Borges says in the prologue to "El otro, el mismo": "It is often forgotten that (dictionaries) are artificial repositories, put together well after the languages they define. The roots of language are irrational and of a magical nature."

Sometimes the same dictionary can be descriptive in some domains and prescriptive in others. For example, according to Ghil'ad Zuckermann, the Oxford English-Hebrew Dictionary is "at war with itself": whereas its coverage (lexical items) and glosses (definitions) are descriptive and colloquial, its vocalization is prescriptive. This internal conflict results in absurd sentences such as hi taharóg otí kshetiré me asíti lamkhonít (she'll tear me apart when she sees what I've done to the car). Whereas hi taharóg otí, literally 'she will kill me', is colloquial, me (a variant of ma 'what') is archaic, resulting in a combination that is unutterable in real life.

Historical dictionaries
A historical dictionary is a specific kind of descriptive dictionary which describes the development of words and senses over time, usually using citations to original source material to support its conclusions.

Dictionaries for natural language processing
In contrast to traditional dictionaries, which are designed to be used by human beings, dictionaries for natural language processing (NLP) are built to be used by computer programs. The final user is a human being but the direct user is a program. Such a dictionary does not need to be able to be printed on paper. The structure of the content is not linear, ordered entry by entry but has the form of a complex network (see Diathesis alternation). Because most of these dictionaries are used to control machine translations or cross-lingual information retrieval (CLIR) the content is usually multilingual and usually of huge size. In order to allow formalized exchange and merging of dictionaries, an ISO standard called Lexical Markup Framework (LMF) has been defined and used among the industrial and academic community.

Other types

 * Bilingual dictionary
 * Collegiate dictionary (American)
 * Learner's dictionary (mostly British)
 * Electronic dictionary
 * Encyclopedic dictionary
 * Monolingual learner's dictionary
 * Advanced learner's dictionary
 * By sound
 * Rhyming dictionary
 * Reverse dictionary (Conceptual dictionary)
 * Visual dictionary
 * Satirical dictionary
 * Phonetic dictionary

Pronunciation
In many languages, such as the English language, the pronunciation of some words is not consistently apparent from their spelling. In these languages, dictionaries usually provide the pronunciation. For example, the definition for the word dictionary might be followed by the International Phonetic Alphabet spelling (in British English) or  (in American English). American English dictionaries often use their own pronunciation respelling systems with diacritics, for example dictionary is respelled as "dĭk′shə-nĕr′ē" in the American Heritage Dictionary. The IPA is more commonly used within the British Commonwealth countries. Yet others use their own pronunciation respelling systems without diacritics: for example, dictionary may be respelled as. Some online or electronic dictionaries provide audio recordings of words being spoken.

Major English dictionaries
• A Dictionary of the English Language by Samuel Johnson (prescriptive)

• The American College Dictionary by Clarence L. Barnhart

• The American Heritage Dictionary of the English Language

• Black's Law Dictionary, a law dictionary

• Brewer's Dictionary of Phrase and Fable

• Canadian Oxford Dictionary

• Century Dictionary

• Chambers Dictionary

• Collins English Dictionary

• Concise Oxford English Dictionary

• Longman Dictionary of Contemporary English / Longman

• Macmillan Dictionary

• Macquarie Dictionary, a dictionary of Australian English

• Merriam-Webster, a dictionary of American English

• Oxford Dictionary of English

• Oxford English Dictionary (descriptive) (well-known as OED/O.E.D.)

• Random House Dictionary of the English Language

• Webster's New World Dictionary (especially the college edition, used as the official desk dictionary of many American press journalists)

Dictionaries of other languages
Histories and descriptions of the dictionaries of other languages on Wikipedia include:

 * Arabic dictionaries
 * Chinese dictionaries
 * Dehkhoda Dictionary (Persian Language)
 * Dutch dictionaries
 * French dictionaries
 * German dictionaries
 * Japanese dictionaries
 * Polish dictionaries
 * Scottish Gaelic dictionaries
 * Scottish Language Dictionaries
 * Sindhi Language Dictionaries

Online dictionaries
The age of the Internet brought online dictionaries to the desktop and, more recently, to the smart phone. David Skinner in 2013 noted that "Among the top ten lookups on Merriam-Webster Online at this moment are holistic, pragmatic, caveat, esoteric and bourgeois. Teaching users about words they don't already know has been, historically, an aim of lexicography, and modern dictionaries do this well." There exist a number of websites which operate as online dictionaries, usually with a specialized focus. Some of them have exclusively user driven content, often consisting of neologisms. Some of the more notable examples are given in List of online dictionaries and Category:Online dictionaries.

license: Creative Commons - Attribution Share-Alike - https://creativecommons.org/licenses/by-sa/4.0/

title: Dictionary


text:
David D. Friedman

David Director Friedman (born February 12, 1945) is an American economist, physicist, legal scholar, and anarcho-capitalist theorist. Although his academic training was in chemistry and physics and not law or economics, he is known for his textbook writings on microeconomics and the libertarian theory of anarcho-capitalism, which is the subject of his most popular book, The Machinery of Freedom. Described by Walter Block as a "free-market anarchist" theorist, Friedman has also authored several other books and articles, including Price Theory: An Intermediate Text (1986), Law's Order: What Economics Has to Do with Law and Why It Matters (2000), Hidden Order: The Economics of Everyday Life (1996), and Future Imperfect (2008).

Life and work
David Friedman is the son of economists Rose and Milton Friedman. He graduated magna cum laude from Harvard University in 1965, with a bachelor's degree in chemistry and physics. He later earned a master's (1967) and a PhD (1971) in theoretical physics from the University of Chicago. Despite his later career, he never took a class for credit in either economics or law. He was a professor of law at Santa Clara University from 2005 to 2017, and a contributing editor for Liberty magazine. He is currently a Professor Emeritus. He is an atheist. His son, Patri Friedman, has also written about libertarian theory and market anarchism, particularly seasteading.

The Machinery of Freedom
In his book The Machinery of Freedom (1973), Friedman sketched a form of anarcho-capitalism where all goods and services including law itself can be produced by the free market. Friedman advocates an incrementalist approach to achieve anarcho-capitalism by gradual privatization of areas that government is involved in, ultimately privatizing the law itself. In the book, he states his opposition to violent anarcho-capitalist revolution.

He advocates a consequentialist version of anarcho-capitalism, arguing for it on a cost–benefit analysis of state versus no state. It is contrasted with the natural-rights approach as propounded most notably by economist and libertarian theorist Murray Rothbard.

Non-academic interests
Friedman is a longtime member of the Society for Creative Anachronism, where he is known as Duke Cariadoc of the Bow. He is known throughout the worldwide society for his articles on the philosophy of recreationism and practical historical recreations, especially those relating to the medieval Middle East. His work is compiled in the popular Cariadoc's Miscellany. He is sometimes credited with founding the largest and longest-running SCA event, the Pennsic War; as king of the Middle Kingdom he challenged the East Kingdom, and later as king of the East accepted the challenge and lost (to himself).

He was a teenage wargamer who taught his school friend, Jack Radey, founder of People's War Games, how to play such wargames as Tactics II. Radey relates how Friedman and himself wrote to Charles S. Roberts claiming that they had found a first turn winning strategy for each of the two sides. Roberts replied that their interpretation of the rules was valid.

He is a long-time science fiction fan, and has written three novels. Harald (Baen Books, 2006) is set in an invented world drawn from European history. Salamander (2011) and its sequel Brothers (2020) are fantasy.

He has spoken in favor of a non-interventionist foreign policy.

Nonfiction

 * 1988. Cariadoc's Miscellany.
 * 1990 (2nd ed.; 1st ed.: 1986). Price Theory: An Intermediate Text. Southwestern Publishing.
 * 1996. Hidden Order: The Economics of Everyday Life. ISBN 0887308856.
 * 2000. Law's Order: What Economics Has to Do with Law and Why It Matters. Princeton Univ. Press. ISBN 0691090092
 * 2005. "The Case for Privacy" in Contemporary Debates in Applied Ethics. Wiley-Blackwell. ISBN 1405115483
 * 2008. Future Imperfect: Technology and Freedom in an Uncertain World. ISBN 0521877326
 * 2015 (3rd ed.; 2nd ed.: 1989; 1st ed.: 1973). The Machinery of Freedom. ISBN 978-1507785607
 * 2019. Legal Systems Very Different from Ours. ISBN 1793386722

Fiction

 * Salamander, 2011
 * Brothers, 2020
 * Brothers, 2020

title: David D. Friedman


text:
Diatomic molecule

Diatomic molecules are molecules composed of only two atoms, of the same or different chemical elements. If a diatomic molecule consists of two atoms of the same element, such as hydrogen (H2) or oxygen (O2), then it is said to be homonuclear. Otherwise, if a diatomic molecule consists of two different atoms, such as carbon monoxide (CO) or nitric oxide (NO), the molecule is said to be heteronuclear. The bond in a homonuclear diatomic molecule is non-polar.

The only chemical elements that form stable homonuclear diatomic molecules at standard temperature and pressure (STP) (or at typical laboratory conditions of 1 bar and 25 °C) are the gases hydrogen (H2), nitrogen (N2), oxygen (O2), fluorine (F2), and chlorine (Cl2), and the liquid bromine (Br2).

The noble gases (helium, neon, argon, krypton, xenon, and radon) are also gases at STP, but they are monatomic. The homonuclear diatomic gases and noble gases together are called "elemental gases" or "molecular gases", to distinguish them from other gases that are chemical compounds.

At slightly elevated temperatures, the halogens bromine (Br2) and iodine (I2) also form diatomic gases. All halogens have been observed as diatomic molecules, except for astatine and tennessine, which are uncertain.

Other elements form diatomic molecules when evaporated, but these diatomic species repolymerize when cooled. Heating ("cracking") elemental phosphorus gives diphosphorus (P2). Sulfur vapor is mostly disulfur (S2). Dilithium (Li2) and disodium (Na2) are known in the gas phase. Ditungsten (W2) and dimolybdenum (Mo2) form with sextuple bonds in the gas phase. Dirubidium (Rb2) is diatomic.

Heteronuclear molecules
All other diatomic molecules are chemical compounds of two different elements. Many elements can combine to form heteronuclear diatomic molecules, depending on temperature and pressure.

Examples are gases carbon monoxide (CO), nitric oxide (NO), and hydrogen chloride (HCl).

Many 1:1 binary compounds are not normally considered diatomic because they are polymeric at room temperature, but they form diatomic molecules when evaporated, for example gaseous MgO, SiO, and many others.

Occurrence
Hundreds of diatomic molecules have been identified in the environment of the Earth, in the laboratory, and in interstellar space. About 99% of the Earth's atmosphere is composed of two species of diatomic molecules: nitrogen (78%) and oxygen (21%). The natural abundance of hydrogen (H2) in the Earth's atmosphere is only of the order of parts per million, but H2 is the most abundant diatomic molecule in the universe. The interstellar medium is dominated by hydrogen atoms.

Molecular geometry
All diatomic molecules are linear and characterized by a single parameter which is the bond length or distance between the two atoms. Diatomic nitrogen has a triple bond, diatomic oxygen has a double bond, and diatomic hydrogen, fluorine, chlorine, iodine, and bromine all have single bonds.

Historical significance
Diatomic elements played an important role in the elucidation of the concepts of element, atom, and molecule in the 19th century, because some of the most common elements, such as hydrogen, oxygen, and nitrogen, occur as diatomic molecules. John Dalton's original atomic hypothesis assumed that all elements were monatomic and that the atoms in compounds would normally have the simplest atomic ratios with respect to one another. For example, Dalton assumed water's formula to be HO, giving the atomic weight of oxygen as eight times that of hydrogen, instead of the modern value of about 16. As a consequence, confusion existed regarding atomic weights and molecular formulas for about half a century.

As early as 1805, Gay-Lussac and von Humboldt showed that water is formed of two volumes of hydrogen and one volume of oxygen, and by 1811 Amedeo Avogadro had arrived at the correct interpretation of water's composition, based on what is now called Avogadro's law and the assumption of diatomic elemental molecules. However, these results were mostly ignored until 1860, partly due to the belief that atoms of one element would have no chemical affinity toward atoms of the same element, and also partly due to apparent exceptions to Avogadro's law that were not explained until later in terms of dissociating molecules.

At the 1860 Karlsruhe Congress on atomic weights, Cannizzaro resurrected Avogadro's ideas and used them to produce a consistent table of atomic weights, which mostly agree with modern values. These weights were an important prerequisite for the discovery of the periodic law by Dmitri Mendeleev and Lothar Meyer.

Excited electronic states
Diatomic molecules are normally in their lowest or ground state, which conventionally is also known as the $$X$$ state. When a gas of diatomic molecules is bombarded by energetic electrons, some of the molecules may be excited to higher electronic states, as occurs, for example, in the natural aurora; high-altitude nuclear explosions; and rocket-borne electron gun experiments. Such excitation can also occur when the gas absorbs light or other electromagnetic radiation. The excited states are unstable and naturally relax back to the ground state. Over various short time scales after the excitation (typically a fraction of a second, or sometimes longer than a second if the excited state is metastable), transitions occur from higher to lower electronic states and ultimately to the ground state, and in each transition results a photon is emitted. This emission is known as fluorescence. Successively higher electronic states are conventionally named $$A$$, $$B$$, $$C$$, etc. (but this convention is not always followed, and sometimes lower case letters and alphabetically out-of-sequence letters are used, as in the example given below). The excitation energy must be greater than or equal to the energy of the electronic state in order for the excitation to occur.

In quantum theory, an electronic state of a diatomic molecule is represented by the molecular term symbol
 * $$^{2S+1} \Lambda (v)^{+/-}_{(g/u)}$$

where $$S$$ is the total electronic spin quantum number, $$\Lambda$$ is the total electronic angular momentum quantum number along the internuclear axis, and $$v$$ is the vibrational quantum number. $$\Lambda$$ takes on values 0, 1, 2, ..., which are represented by the electronic state symbols $$\Sigma$$, $$\Pi$$, $$\Delta$$,.... For example, the following table lists the common electronic states (without vibrational quantum numbers) along with the energy of the lowest vibrational level ($$v=0$$) of diatomic nitrogen (N2), the most abundant gas in the Earth's atmosphere.

The subscripts and superscripts after $$\Lambda$$ give additional quantum mechanical details about the electronic state. The superscript $$+$$ or $$-$$ determines whether reflection in a plane containing the internuclear axis introduces a sign change in the wavefunction. The sub-script $$g$$ or $$u$$ applies to molecules of identical atoms, and when reflecting the state along a plane perpendicualr to the molecular axis, states that does not change are labelled $$g$$ (gerade), and states that change sign are labelled $$u$$ (ungerade).

The aforementioned fluorescence occurs in distinct regions of the electromagnetic spectrum, called "emission bands": each band corresponds to a particular transition from a higher electronic state and vibrational level to a lower electronic state and vibrational level (typically, many vibrational levels are involved in an excited gas of diatomic molecules). For example, N2 $$A$$-$$X$$ emission bands (a.k.a. Vegard-Kaplan bands) are present in the spectral range from 0.14 to 1.45 μm (micrometres). A given band can be spread out over several nanometers in electromagnetic wavelength space, owing to the various transitions that occur in the molecule's rotational quantum number, $$J$$. These are classified into distinct sub-band branches, depending on the change in $$J$$. The $$R$$ branch corresponds to $$\Delta J = +1$$, the $$P$$ branch to $$\Delta J = -1$$, and the $$Q$$ branch to $$\Delta J = 0$$. Bands are spread out even further by the limited spectral resolution of the spectrometer that is used to measure the spectrum. The spectral resolution depends on the instrument's point spread function.

Energy levels
The molecular term symbol is a shorthand expression of the angular momenta that characterize the electronic quantum states of a diatomic molecule, which are also eigenstates of the electronic molecular Hamiltonian. It is also convenient, and common, to represent a diatomic molecule as two-point masses connected by a massless spring. The energies involved in the various motions of the molecule can then be broken down into three categories: the translational, rotational, and vibrational energies.The theoretical study of the rotational energy levels of the diatomic molecules can be described using the below description of the rotational energy levels. While the study of vibrational energy level of the diatomic molecules can be described using the harmonic oscillator approximation or using the quantum vibrational interaction potentials. These potentials give more accurate energy levels because they take multiple vibrational effects into account.

Concerning history, the first treatment of diatomic molecules with quantum mechanics was made by Lucy Mensing in 1926.

Translational energies
The translational energy of the molecule is given by the kinetic energy expression:
 * $$E_\text{trans}=\frac{1}{2}mv^2$$

where $$m$$ is the mass of the molecule and $$v$$ is its velocity.

Rotational energies
Classically, the kinetic energy of rotation is
 * $$E_\text{rot} = \frac{L^2}{2 I} \,$$
 * where
 * $$L \,$$ is the angular momentum
 * $$I \,$$ is the moment of inertia of the molecule

For microscopic, atomic-level systems like a molecule, angular momentum can only have specific discrete values given by
 * $$L^2 = \ell(\ell+1) \hbar^2 \,$$
 * where $$\ell$$ is a non-negative integer and $$\hbar$$ is the reduced Planck constant.

Also, for a diatomic molecule the moment of inertia is
 * $$I = \mu r_{0}^2 \,$$
 * where
 * $$\mu \,$$ is the reduced mass of the molecule and
 * $$r_{0} \,$$ is the average distance between the centers of the two atoms in the molecule.

So, substituting the angular momentum and moment of inertia into Erot, the rotational energy levels of a diatomic molecule are given by:

Vibrational energies
Another type of motion of a diatomic molecule is for each atom to oscillate—or vibrate—along the line connecting the two atoms. The vibrational energy is approximately that of a quantum harmonic oscillator:

 * $$E_\text{vib} = \left(n+\frac{1}{2} \right)\hbar \omega \ \ \ \ \ n=0,1,2,.... \,$$
 * where
 * $$n$$ is an integer
 * $$\hbar$$ is the reduced Planck constant and
 * $$\omega$$ is the angular frequency of the vibration.

Comparison between rotational and vibrational energy spacings
The spacing, and the energy of a typical spectroscopic transition, between vibrational energy levels is about 100 times greater than that of a typical transition between rotational energy levels.

Hund's cases
The good quantum numbers for a diatomic molecule, as well as good approximations of rotational energy levels, can be obtained by modeling the molecule using Hund's cases.

Mnemonics
The mnemonics BrINClHOF, pronounced "Brinklehof", HONClBrIF, pronounced "Honkelbrif", “HOBrFINCl”, pronounced “Hoberfinkel”, and HOFBrINCl, pronounced "Hofbrinkle", have been coined to aid recall of the list of diatomic elements. Another method, for English-speakers, is the sentence: "Never Have Fear of Ice Cold Beer" as a representation of Nitrogen, Hydrogen, Fluorine, Oxygen, Iodine, Chlorine, Bromine.

title: Diatomic molecule