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Right of return

The right of return is a principle in international law which guarantees everyone's right of voluntary return to, or re-entry to, their country of origin or of citizenship. The right of return is part of the broader human rights concept freedom of movement and is also related to the legal concept of nationality. While many states afford their citizens the right of abode, the right of return is not restricted to citizenship or nationality in the formal sense. It allows stateless persons and for those born outside their country to return for the first time, so long as they have maintained a "genuine and effective link".

The right is formulated in several modern treaties and conventions, most notably in the 1948 Universal Declaration of Human Rights, the 1966 International Covenant on Civil and Political Rights and the 1948 Fourth Geneva Convention. Legal scholars have argued that one or more of these international human rights instruments have attained the status of customary international law and that the right of return is therefore binding on non-signatories to these conventions.

The right of return is often invoked by representatives of refugee groups to assert that they have a right to return to the country from which they were displaced.

History
The right to leave any country and to return to one's own country are regarded as human rights and founded on natural law.

Ancient precedents
While the right of return was not explicitly recognized in antiquity, exile, being explicitly refused permission to return home, was a common punishment for severe crimes. The topic was discussed extensively by antique writers. For example, Teles of Megara in his diatribe On Exile wrote "But exiles are not allowed to return home, and this is a severe restriction of their freedom."

During antiquity, groups of people were frequently deported or uprooted from their cities and homeland, often as part of conquest or as a punishment for rebellion. In some cases they were allowed or encouraged to return, typically after the balance of military and political forces had changed.

A well-known example is the return to Zion, by which King Cyrus the Great granted the Jews expelled from Judah to Babylon the option to return to their ancestral homeland and rebuild Jerusalem. Recorded in the Hebrew Bible (Book of Ezra and Book of Nehemiah) this case is often cited as a precedent by modern Zionists and also inspired other groups seeking to pursue their own return.

During the Peloponnesian War, Athens expelled and scattered the inhabitants of Melos, Aegina and other cities (some of them being sold into slavery). Following the victory of Sparta, the Spartan general Lysander in 405 BC made a concerted effort to gather these exiles and restore them to their original cities.

Magna Carta
The first codified law guaranteeing a right of return can be found in the English charter Magna Carta from 1215: "In future it shall be lawful for any man to leave and return to our kingdom unharmed and without fear, by land or water, preserving his allegiance to us, except in time of war, for some short period, for the common benefit of the realm. People that have been imprisoned or outlawed in accordance with the law of the land, people from a country that is at war with us, and merchants – who shall be dealt with as stated above – are excepted from this provision."

French Constitution of 1791
Another early example of national law recognizing the Right of Return was the French constitution of 1791, enacted on 15 December 1790: "the freedom of everyone to go, to stay, or to leave, without being halted or arrested unless in accordance with procedures established by the Constitution."

The constitution put an end to the centuries-long persecution and discrimination of Huguenots (French Protestants).

Concurrently with making all Protestants resident in France into full-fledged citizens, the law enacted on December 15, 1790 stated that: "All persons born in a foreign country and descending in any degree of a French man or woman expatriated for religious reason are declared French nationals (naturels français) and will benefit to rights attached to that quality if they come back to France, establish their domicile there and take the civic oath."

The revocation of the Edict of Nantes and expulsion of the Huguenots had taken place more than a century earlier, and there were numerous Huguenot emigrants to other countries, where they often intermarried with the population of the host country (see Edict of Potsdam). Therefore, the law potentially conferred French citizenship on numerous Britons, Germans, South Africans and others – though only a fraction actually took advantage of it. This option for Huguenot descendants to gain French citizenship remained open until 1945, when it was abolished – since after the occupation of France, the French were unwilling to let Germans of Huguenot origin take advantage of it.

Schleswig plebiscites, 1920
In the aftermath of the Second Schleswig War of 1864, the previously Danish-ruled territory of Schleswig became part of Imperial Germany. A significant number of inhabitants, known as "optants", chose to retain their Danish citizenship and refused to take up a German one. Consequently, they were expelled from the area by Prussian authorities. Half a century later, following the German defeat in the First World War, a plebiscite was held in 1920 to determine the future of the area. The Danish government asked the Allied Powers to let these expelled ethnic Danes and their descendants return to Schleswig and take part in the plebiscite. This was granted, though many of the optants had in the meantime emigrated to the United States, and most of these did not actually come back.

Legal understanding of the right
The right of return principle has been codified in a number of international instruments, including:

Hague Regulations (HR), article 20:

1. After the conclusion of peace, the repatriation of prisoners of war shall be carried out as quickly as possible.

It has been argued that if the HR require the repatriation of prisoners, then it is "obvious" that civilians displaced during conflict must also be allowed to repatriate.

Universal Declaration of Human Rights (UDHR), article 13:

 * 1) Everyone has the right to freedom of movement and residence within the borders of each State.
 * 2) Everyone has the right to leave any country, including his own, and to return to his country.

International Covenant on Civil and Political Rights (ICCPR) article 12(4):

1. No one shall be arbitrarily deprived of the right to enter his own country.

Fourth Geneva Convention, article 49:

1. Individual or mass forcible transfers, as well as deportations of protected persons from occupied territory to the territory of the Occupying Power or to that of any other country, occupied or not, are prohibited, regardless of their motive. Nevertheless, the Occupying Power may undertake total or partial evacuation of a given area if the security of the population or imperative military reasons so demand. ... Persons thus evacuated shall be transferred back to their homes as soon as hostilities in the area in question have ceased.

Convention on the Elimination of All Forms of Racial Discrimination, article 5d(ii):

"The right to leave any country, including one's own, and to return to one's country."

Some controversy exists among scholars on how these articles should be interpreted.

"His own country"
The landmark International Court of Justice case the Nottebohm case of 1955 is often cited as staking out more criteria as to what "one's country" should be. The court ruled that there needed to be a "genuine and effective" link between the individual and the country. Among the criteria listed for such a link were "a close and enduring connection", "tradition", "establishment", "interests" and "family ties". The 1955 ruling has been supplanted by more recent conventions and court rulings.

There is some disagreement as to what "his own" and "his country" means in the ICCPR and UDHR. According to the United Nations Human Rights Committee's authoritative interpretation from 1999:

"The scope of 'his own country' is broader than the concept 'country of his nationality'. It is not limited to nationality in a formal sense, that is, nationality acquired at birth or by conferral; it embraces, at the very least, an individual who, because of his or her special ties to or claims in relation to a given country, cannot be considered to be a mere alien. This would be the case, for example, of nationals of a country who have been stripped of their nationality in violation of international law, and of individuals whose country of nationality has been incorporated in or transferred to another national entity, whose nationality is being denied them. The right of a person to enter his or her own country recognizes the special relationship of a person to that country ... It includes not only the right to return after having left one’s own country; it may also entitle a person to come to the country for the first time if he or she was born outside the country."

According to Agterhuis, the record of negotiations - the travaux préparatoires - of the ICCPR reveals that the wording of article 12(4) was changed from "the right to return to one's country" to "the right to enter one's country" was made in order to include nationals or citizens born outside the country and who have never lived therein.

Mass displacement
Some disagreement exists on whether the right of return is applicable to situations in which whole ethnic groups have been forcibly displaced. Ruth Lapidoth from the Jerusalem Center for Public Affairs has argued, by citing Stig Jägerskiöld from his 1966 commentary of ICCPR, that the right was not intended to protect groups of displaced people:

"... [it] is intended to apply to individuals asserting an individual right. There was no intention here to address the claims of masses of people who have been displaced as a by-product of war or by political transfers of territory or population, such as the relocation of ethnic Germans from Eastern Europe during and after the Second World War, the flight of the Palestinians from what became Israel, or the movement of Jews from the Arab countries."

Hurst Hannum has made a similar argument:

"There is no evidence that mass movements of groups such as refugees or displaced persons were to be intended to be included within the scope of article 12 of the Covenant by its drafters."

Austrian human rights lawyer Manfred Nowak has argued the opposite position, that the right of return applies "even if masses of people are claiming this right". Bracka has argued similarly:

"At any rate, what seems clear is that neither the text nor the travaux préparatoires of the relevant UDHR, ICCPR and CERD provisions actually support circumscribing [the right of] return in this way [to exclude situations of mass displacement]. Firstly, there is no indication that the drafters considered the applicability of the freedom of movement principle to members of displaced populations. And although it may have been assumed at the time that such a scenario would receive discussion in 'some other body of law', this is not synonymous with an intention to limit these articles to isolated individuals. Secondly, nowhere in the actual text is the operation of the right of return qualified on the basis of group affiliation. Rather, in each instance, the relevant language refers to 'everyone'. In addition, the HRC in General Comment 27 affirms this reading in so far as it states: '[t]he right to return is of the utmost importance for refugees seeking voluntary repatriation. It also implies prohibition of enforced population transfers or mass expulsions to other countries'. Thirdly, whilst the right of return in art 12(4) of the ICCPR is presented as an individual right, Quigley confirms that 'this is also true of most rights in international human rights instruments'. Indeed, the movement of people has historically taken on a collective dimension. Accordingly, to deny the availability of human rights simply because individuals form part of a mass group would render those rights illusory."

Eric Rosand, legal advisor to the US State Department, used the same argument:

"Although political negotiations and the issue of self-determination may be appropriate in situations involving mass displacement, nothing in the text or travaux préparatoires of the relevant provisions of the UDHR, ICCPR, or ICERD limits the application of the right of return to individual instances of refusals to repatriate. In fact, based on a close review of these documents, one could conclude that the drafters did not intend to except mass movements of refugees and displaced persons from this right, particularly since the UDHR, the ICCPR, and the ICERD do not indicate that the right to return should be linked to one's group status. In each instance, the relevant language refers to 'everyone' having a right to return."

Rosand discusses the views of scholars who do not consider the right of return to be applicable under mass displacement but concludes:

"In the final decade of this century, however, the world now condemns such population transfers, which, along with mass expulsions, are deemed to violate important principles of international law. ... Moreover, the right to return in both the UDHR and the ICCPR was the basis for guaranteeing this right in recently signed peace agreements in order to resolve conflicts in Rwanda and Georgia, both of which produced hundreds of thousands of refugees and displaced persons. ... Although the actual return of these groups may, in the end, be determined by political feasibility, this should not prevent the international community from grounding their return in international law. ... In short, there is a difference between acknowledging that a right to return exists although in certain instances it may not be implementable due to the unresolved political situation and declaring that the issue of the return of large groups is beyond the scope of international law and resolvable only as part of ongoing political negotiations."

Resettled refugees
According to Masri, refugee status is independent of right of return. Thus, refugees who acquire new nationalities in their host countries do not necessarily lose their right to return to the countries they left. Masri argues that the resettlement "weakens the link" between the refugee and the source country but that this weakening is not enough to automatically lead to the deprivation of rights.

Regional treaties
The right of return is also found in many regional treaties, such as article 12(2) of the African Charter on Human and Peoples' Rights: "Every individual shall have the right to leave any country including his own, and to return to his country. This right may only be subject to restrictions, provided for by law for the protection of national security, law and order, public health or morality."

The right is also found in article 3(2) of the European Convention on Human Rights; "[n]o one shall be deprived of the right to enter the territory of the state of which he is a national" and article 22(5) of the American Convention on Human Rights: "[n]o one can be expelled from the territory of the state of which he is a national or be deprived of the right to enter it." In these conventions the word "national" is used which is considered narrower than "his own country" in article 12(4) of the ICCPR.

Right of return in case law
Few cases have dealt with the right of return principle. In 1996, the European Court of Human Rights (ECHR) ruled in a landmark case known as Loizidou v Turkey. Mrs Titina Loizidou was a Greek-Cypriot refugee displaced from Northern Cyprus and prevented from returning by Turkey. The court ruled that Turkey had violated Mrs Loizidou's human rights, that she should be allowed to return to her home and that Turkey should pay damages to her.

In a similar case, petitioners for the Chagossians asked the ECHR in 2005 to rule about their removal from Diego Garcia by the British government in the 1960s. The court ruled in 2012 that their case was inadmissible and that by accepting compensation, the islanders had forfeited their claim:

"The Court notably found that the heart of the applicants' claims under the European Convention on Human Rights was the callous and shameful treatment which they or their antecedents had suffered during their removal from the Chagos islands. These claims had, however, been raised in the domestic courts and settled, definitively. In accepting and receiving compensation, the applicants had effectively renounced bringing any further claims to determine whether the expulsion and exclusion from their homes had been unlawful and breached their rights and they therefore could no longer claim to be victims of a violation of the Convention."

Circassians
Circassians are an indigenous ethnic group originating from the northwestern Caucasus. Throughout the 19th century, the Russian Empire adopted a policy to eradicate Circassians from their ancestral homelands, pushing most surviving Circassians into the diaspora. Many Circassians have expressed an interest in returning to Circassia, particularly Circassians fleeing the conflict in Syria.

Georgian refugees and internally displaced people
During Abkhazia's war of secession in 1992–1993 and the second Abkhazia war in 1998, 200,000–250,000 Georgian civilians became internally displaced people (IDPs) and refugees. Abkhazia, while formally agreeing to repatriation, has hindered the return of refugees both officially and unofficially for more than fifteen years.

Greek-Cypriots
During the Turkish invasion of Cyprus, 40% of the Greek-Cypriot population as well as over half of the Turk-Cypriot population of the island were displaced. The island was divided along ethnic lines and most of the Greek-Cypriot displaced people were not allowed to return to their homes in the northern Turk-Cypriot side and vice versa.

Plans for a solution of the conflict has centered around bilateral agreements of population exchange, such as the Third Vienna Agreement reached in 1975 or the proposed Annan Plan of 2004. In these plans, the right of return was to be severely limited with respect to Greek-Cypriot internally displaced people/refugees to districts such as Kyrenia, Morphou, Famagusta, and parts of Nicosia, despite judgements of the European Court of Human Rights in cases such as Loizidou v. Turkey, and numerous UN resolutions recognizing the right of return (such as SC 361 and GA 3212). Two referendums on the Annan Plan were held in April 2004, separately along ethnic lines. The Annan Plan was overwhelmingly rejected in the Greek-Cypriot referendum.

The right of return continues to remain a stumbling block to the settlement of the Cyprus problem.

Diego Garcia Chagossians
The Chagossians, an ethnic group residing on the island of Diego Garcia in the Indian Ocean, were expelled to Mauritius in the 1960s, in connection with the erection of an U.S. Military strategic military installation on the island. Ever since, the Chagossians have been conducting a persistent political and legal struggle to return to Diego Garcia. As of 2007, their right to return was recognised by several British courts but the UK government had failed to implement it.

Palestinians
State succession arises when there is a definitive replacement of one state by another in respect of sovereignty over a given political territory, in conformity with international law. Experts argue that, under those principles, Palestinian citizens who fled or were expelled from the areas that became Israel automatically acquired Israeli nationality with the creation of the state in 1948. Consequently, these individuals, based on their de jure nationality, could claim a right to return.

Abkhazia (self-declared)
The law on the repatriation of self-declared Republic of Abkhazia gives the right of return to the ethnic Abkhaz and Abazins who are the descendants of the refugees who left Abkhazia due to the 19th-century conflicts. The State Repatriation Committee provides support to the repatriates.

Armenia
Article 14 of the Constitution of Armenia (1995) provides that "[i]ndividuals of Armenian origin shall acquire citizenship of the Republic of Armenia through a simplified procedure." This provision is consistent with the Declaration on Independence of Armenia, issued by the Supreme Soviet of the Republic of Armenia in 1989, which declared at article 4 that "Armenians living abroad are entitled to the citizenship of the Republic of Armenia".

Austria
Under Section 58c of the Austrian Citizenship Act (Staatsbürgerschaftsgesetz), Austrians and their descendants who were persecuted or feared persecution by Nazi Germany can become Austrian citizens. While Austria does not allow dual citizenship in most circumstances, people who receive citizenship under § 58c may keep their previous citizenship. However, if they later receive another country's citizenship, they must renounce their Austrian citizenship and may not re-apply.

Finland
People of Finnish origin may receive citizenship by declaration, which is faster and cheaper than naturalization and has fewer requirements. People of Finnish origin can be: 1) children, born abroad, of a Finnish father; 2) 12–17-year-old adopted children; 3) former Finnish citizens; 4) citizens of another Nordic country; 5) 18-22-year-olds with a long residency in Finland. Formerly, Finland also accepted returnees with a Soviet passport (or post-Soviet passport) where the ethnicity was marked as Finnish. This allowed the immigration of Ingrian Finns and other Finns who had remained in the Soviet Union. People who served in the Finnish Defence Forces or Finnish people evacuated by German or Finnish authorities from occupied areas to Finland during World War II also qualified as returnees. However, these options are no longer available, and applicants must qualify for ordinary naturalization instead.

France
Another early example of national law recognizing the Right of Return was the French constitution of 1791, enacted on 15 December 1790: "the freedom of everyone to go, to stay, or to leave, without being halted or arrested unless in accordance with procedures established by the Constitution."

The constitution put an end to the centuries-long persecution and discrimination of Huguenots (French Protestants).. Concurrently with making all Protestants resident in France into full-fledged citizens, the law enacted on December 15, 1790 stated that: "All persons born in a foreign country and descending in any degree of a French man or woman expatriated for religious reason are declared French nationals (naturels français) and will benefit to rights attached to that quality if they come back to France, establish their domicile there and take the civic oath."

The revocation of the Edict of Nantes and expulsion of the Huguenots had taken place more than a century earlier, and there were extensive Huguenot diasporas in many countries, where they often intermarried with the population of the host country. Therefore, the law potentially conferred French citizenship on numerous Britons, Germans, South Africans and others – though only a fraction actually took advantage of it. This option for Huguenot descendants to gain French citizenship remained open until 1945, when it was abolished - since after the Occupation of France, the French were unwilling to let Germans of Huguenot origin to take advantage of it. In October 1985, French President François Mitterrand issued a public apology to the descendants of Huguenots around the world.

Germany
German law allows (1) people descending from German nationals of any ethnicity or (2) people of ethnic German descent and living in countries of the former Warsaw Pact (as well as Yugoslavia) the right to "return" to Germany and ("re")claim German citizenship (Aussiedler/Spätaussiedler, "late emigrants"). After legislative changes in late 1992 this right is de facto restricted to ethnic Germans from the former Soviet Union. As with many legal implementations of the right of return, the "return" to Germany of individuals who may never have lived in Germany based on their ethnic origin or their descent from German nationals has been controversial. The law is codified in paragraph 1 of Article 116 of the Basic Law for the Federal Republic of Germany, which provides access to German citizenship for anyone "who has been admitted to the territory of the German Reich within the boundaries of December 31, 1937, as a refugee or expellee of German ethnic origin or as the spouse or descendant of such person". Those territories had a Polish minority, which also had German citizenship and after World War II lived in Poland. These Polish people are also Aussiedler or Spätaussiedler and came especially in the 1980s to Germany, see Emigration from Poland to Germany after World War II. For example Lukas Podolski and Eugen Polanski became German citizens by this law. Paragraph 2 of Article 116 also provides that "Former German citizens who between 30 January 1933 and 8 May 1945 were deprived of their citizenship on political, racial or religious grounds, and their descendants, shall on application have their citizenship restored". The historic context for Article 116 was the eviction, following World War II, of an estimated 9 million foreign ethnic Germans from other countries in Central and Eastern Europe. Another 9 million German nationals in the former eastern German territories, over which Joseph Stalin and eastern neighbour states extended military hegemony in 1945, were expelled as well. These expellees and refugees, known as Heimatvertriebene, were given refugee status and documents, and—as to foreign ethnic Germans—also West German citizenship (in 1949), and resettled in West Germany. The discussion of possible compensation continues; this, however, has been countered by possible claims for war compensation from Germany's eastern neighbours, pertaining to both Germany's unconditional surrender and the series of population transfers carried out under the instruments of Potsdam. Between 1950 and 2016 it is estimated that up to 1,445,210 Aussiedler/Spätaussiedler and their family members, including many ethnic Poles according to Deutsche Welle (for example Lukas Podolski and Eugen Polanski), emigrated from Poland.

Ghana
Ghana allows people with African ancestry to apply for and be granted the right to stay in Ghana indefinitely, known as the Right of Abode.

Greece
Various phenomena throughout Greek history (the extensive colonization by classical Greek city states, the vast expansion of Greek culture in Hellenistic times, the large dominions at times held by the Greek-speaking Byzantine Empire, and the energetic trading activity by Greeks under the Ottomans) all tended to create Greek communities far beyond the boundaries of modern Greece.

Recognizing this situation, Greece grants citizenship to broad categories of people of ethnic Greek ancestry who are members of the Greek diaspora, including individuals and families whose ancestors have been resident in diaspora communities outside the modern state of Greece for centuries or millennia.

"Foreign persons of Greek origin", who neither live in Greece nor hold Greek citizenship nor were necessarily born there, may become Greek citizens by enlisting in Greece's military forces, under article 4 of the Code of Greek Citizenship, as amended by the Acquisition of Greek Nationality by Aliens of Greek Origin Law (Law 2130/1993). Anyone wishing to do so must present a number of documents, including "[a]vailable written records ... proving the Greek origin of the interested person and his ancestors".

Albania has demanded since the 1940s that Greece grant a right of return to the Muslim Cham Albanians, who were expelled from the Greek region of Epirus between 1944 and 1945, at the end of World War II – a demand firmly rejected by the Greeks (see Cham issue).

Hungary
In 2010, Hungary passed a law granting citizenship and the right of return to descendants of Hungarians living mostly on the former territory of the Kingdom of Hungary and now residing in Hungary's neighbouring countries. Slovakia, which has 500,000 ethnic Magyar citizens (10% of its population), objected vociferously.

Ireland
Present Irish nationality law states that any person with a grandparent born on the island of Ireland can claim Irish nationality by enrollment in the Foreign Births Register. Additionally, the law permits the Minister of Justice to waive the residency requirements for naturalization for a person of "Irish descent or Irish associations".

Israel
The Law of Return is legislation enacted by Israel in 1950, that gives all Jews, people of Jewish ancestry up to at least one Jewish grandparent, and their spouses the right to immigrate to and settle in Israel and obtain citizenship, and obliges the Israeli government to facilitate their immigration. Originally, the law applied to Jews only, until a 1970 amendment stated that the rights "are also vested in a child and a grandchild of a Jew, the spouse of a Jew, the spouse of a child of a Jew and the spouse of a grandchild of a Jew". This resulted in several hundreds of thousands of people fitting the above criteria immigrating to Israel (mainly from the former Soviet Union) but not being recognized as Jews by the Israeli religious authorities, which on the basis of halakha recognize only the child of a Jewish mother as being Jewish, or a proselyte to Judaism. Moreover, some of these immigrants, though having a Jewish grandparent, are known to be practicing Christians. People who would be otherwise eligible for this law can be excluded if they can reasonably be considered to constitute a danger to the welfare of the state, have a criminal past, or are wanted fugitives in their countries with the exception of persecution victims. Jews who converted to another religion can also be denied the right of return. Since its inception in 1948, over three million Jews have immigrated to Israel.

Latvia
According to the law passed in 2013, any person who themself or whose parent or grandparent had Latvian or Livonian ethnicity, did not voluntarily chose a different ethnicity and lived on Latvian territory between 1881 and 17 June 1940, may register Latvian citizenship upon providing proofing documents and passing a language exam.

Poland
From the Constitution of Poland, Article 52(5): "Anyone whose Polish origin has been confirmed in accordance with statute may settle permanently in Poland."

Portugal
On April 12, 2013, the Portuguese parliament unanimously approved a measure that allows the descendants of Jews expelled from Portugal in the 16th century to become Portuguese citizens.

Romania
Romanian citizenship can be regained or granted to individuals who were Romanian citizens and who lost it for reasons beyond their control or whose citizenship was revoked involuntarily. This legal provision also applies in the case of descendants of former Romanian citizens up to the third degree.

Russia
The Russian Federation offers citizenship to individuals descended from Russian ancestors who can demonstrate an affinity for Russian culture and, preferably, speak Russian. Concern about Russia's shrinking population prompted the program. This has had a positive effect because this has not only reversed Russia's population decline but has also increased the birth rate. Officials estimate that 25 million members of the Russian diaspora are eligible for nationality. The Foreign Ministry has sent emissaries to countries around the world to urge the descendants of Russian emigrants to return home. The majority of these emigrants have returned from Ukraine, many of them young men looking for better education and job opportunities.

Spain
Sephardi Jews were expelled from Spain in 1492. Despite the requirement by general rule for obtaining Spanish nationality after five years of residence in Spain, by royal decree on 20 December 1924, Sephardi Jews can obtain Spanish nationality with two years of residence in Spain. From 1924 until 2015 Sephardi Jews living abroad could also ask the Spanish Government for a conferment of Spanish nationality, but the Government enjoyed full discretion as to the decision whether to grant Spanish nationality. On 24 June 2015, the Spanish Parliament approved the 12/2015 Act, the Law Granting the Nationality to Sephardi Jews, that grants the Spanish nationality automatically to Sephardi Jews living abroad, provided they can prove that they are descendants of the Sephardi Jews expelled in 1492.

In 2007, the Spanish Parliament approved the 57/2007 Act, the Law of Historical Memory. The 57/2007 Act provides for the descendants of Spaniards living abroad that left Spain because of political persecution during the Civil War and Franco's dictatorship – that is the period between 1936 and 1975 – to obtain Spanish nationality.

Finally, following the Anglo-Dutch capture of Gibraltar in August 1704 during the War of the Spanish Succession, the Spanish population left, citing their loyalty to the Bourbons and establishing themselves in the surrounding area (which has come to be known as the "Campo de Gibraltar"). The Spanish population established institutions similar to those they maintained in Gibraltar, including the census and the archives in the City of San Roque, which is the city "where Gibraltar lives on". Some of the population's descendants have cited the right of return in order to return to Gibraltar, although their requests have not been currently addressed by the Spanish government.

title: Right of return


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Nonmetal

In the context of the periodic table a nonmetal is a chemical element that mostly lacks distinctive metallic properties. They range from colorless gases like hydrogen to shiny crystals like iodine. Physically, they are usually lighter (less dense) than elements that form metals and are often poor conductors of heat and electricity. Chemically, nonmetals have relatively high electronegativity or usually attract electrons in a chemical bond with another element, and their oxides tend to be acidic.

Seventeen elements are widely recognized as nonmetals. Additionally, some or all of six borderline elements (metalloids) are sometimes counted as nonmetals.

The two lightest nonmetals, hydrogen and helium, together make up about 98% of the mass of the observable universe. Five nonmetallic elements—hydrogen, carbon, nitrogen, oxygen, and silicon—make up the bulk of Earth's atmosphere, biosphere, crust and oceans.

Industrial uses of nonmetals include in electronics, energy storage, agriculture, and chemical production.

Most nonmetallic elements were identified in the 18th and 19th centuries. While a distinction between metals and other minerals had existed since antiquity, a basic classification of chemical elements as metallic or nonmetallic emerged only in the late 18th century. Since then over thirty properties have been suggested as criteria for distinguishing nonmetals from metals.

Definition and applicable elements

 * Unless otherwise noted, this article describes the stable form of an element at standard temperature and pressure (STP).

Nonmetallic chemical elements are often described as lacking properties common to metals, namely shininess, pliability, good thermal and electrical conductivity, and a general capacity to form basic oxides. There is no widely-accepted precise definition; any list of nonmetals is open to debate and revision. The elements included depend on the properties regarded as most representative of nonmetallic or metallic character.

Fourteen elements are almost always recognized as nonmetals: Hydrogen · Nitrogen · Oxygen · Sulfur Fluorine · Chlorine · Bromine · Iodine Helium · Neon · Argon · Krypton · Xenon · Radon

Three more are commonly classed as nonmetals, but some sources list them as "metalloids", a term which refers to elements regarded as intermediate between metals and nonmetals: Carbon · Phosphorus · Selenium

One or more of the six elements most commonly recognized as metalloids are sometimes instead counted as nonmetals: Boron · Silicon · Germanium · Arsenic · Antimony · Tellurium

About 15–20% of the 118 known elements are thus classified as nonmetals.

Physical
Nonmetals vary greatly in appearance, being colorless, colored or shiny. For the colorless nonmetals (hydrogen, nitrogen, oxygen, and the noble gases), no absorption of light happens in the visible part of the spectrum, and all visible light is transmitted. The colored nonmetals (sulfur, fluorine, chlorine, bromine) absorb some colors (wavelengths) and transmit the complementary or opposite colors. For example, chlorine's "familiar yellow-green colour ... is due to a broad region of absorption in the violet and blue regions of the spectrum". The shininess of boron, graphite (carbon), silicon, black phosphorus, germanium, arsenic, selenium, antimony, tellurium, and iodine is a result of varying degrees of metallic conduction where the electrons can reflect incoming visible light.

About half of nonmetallic elements are gases under standard temperature and pressure; most of the rest are solids. Bromine, the only liquid, is usually topped by a layer of its reddish-brown fumes. The gaseous and liquid nonmetals have very low densities, melting and boiling points, and are poor conductors of heat and electricity. The solid nonmetals have low densities and low mechanical strength (often being brittle or crumbly), and a wide range of electrical conductivity.

This diversity in form stems from variability in internal structures and bonding arrangements. Covalent nonmetals existing as discrete atoms like xenon, or as small molecules, such as oxygen, sulfur, and bromine, have low melting and boiling points; many are gases at room temperature, as they are held together by weak London dispersion forces acting between their atoms or molecules, although the molecules themselves have strong covalent bonds. In contrast, nonmetals that form extended structures, such as chains of up to 1,000 selenium atoms, sheets of carbon atoms in graphite, or three-dimensional lattices of silicon atoms have higher melting and boiling points, and are all solids, as it takes more energy to overcome their stronger bonding. Nonmetals closer to the left or bottom of the periodic table (and so closer to the metals) often have metallic interactions between their molecules, chains, or layers; this occurs in boron, carbon, phosphorus, arsenic, selenium, antimony, tellurium and iodine.

Covalently bonded nonmetals often share only the electrons required to achieve a noble gas electron configuration. For example, nitrogen forms diatomic molecules featuring a triple bonds between each atom, both of which thereby attain the configuration of the noble gas neon. Antimony's larger atomic size prevents triple bonding, resulting in buckled layers in which each antimony atom is singly bonded with three other nearby atoms.

Good electrical conductivity occurs when there is metallic bonding, however the electrons in nonmetals are often not metallic. Good electrical and thermal conductivity associated with metallic electrons is seen in carbon (as graphite, along its planes), arsenic, and antimony. Good thermal conductivity occurs in boron, silicon, phosphorus, and germanium; such conductivity is transmitted though vibrations of the crystalline lattices of these elements. Moderate electrical conductivity is observed in the semiconductors boron, silicon, phosphorus, germanium, selenium, tellurium, and iodine.

Plasticity, which depends upon the movement of dislocations, occurs under limited circumstances in white phosphorus (soft as wax, pliable and can be cut with a knife, at room temperature), in plastic sulfur, and in selenium which can be drawn into wires from its molten state. Graphite is a standard solid lubricant where dislocations move very easily in the basal planes.

Allotropes
Over half of the nonmetallic elements exhibit a range of less stable allotropic forms, each with distinct physical properties. For example, carbon, the most stable form of which is graphite, can manifest as diamond, buckminsterfullerene, amorphous and paracrystalline variations. Allotropes also occur for nitrogen, oxygen, phosphorus, sulfur, selenium, the six metalloids, and iodine.

Chemical
Nonmetals have relatively high values of electronegativity, and their oxides are usually acidic. Exceptions may occur if a nonmetal is not very electronegative, or if its oxidation state is low, or both. These non-acidic oxides of nonmetals may be amphoteric (like water, H2O ) or neutral (like nitrous oxide, N2O ), but never basic.

Nonmetals tend to gain or share electrons during chemical reactions, in contrast to metals which tend to donate electrons. This behavior is closely related to the stability of electron configurations in the noble gases, which have complete outer shells. These tendencies in nonmetallic elements are succinctly summarized by the duet and octet rules of thumb.

They typically exhibit higher ionization energies, electron affinities, and standard electrode potentials than metals. Generally, the higher these values are (including electronegativity) the more nonmetallic the element tends to be. For example, the chemically very active nonmetals fluorine, chlorine, bromine, and iodine have an average electronegativity of 3.19—a figure higher than that of any metallic element.

The chemical distinctions between metals and nonmetals primarily stem from the attractive force between the positive nuclear charge of an individual atom and its negatively charged outer electrons. From left to right across each period of the periodic table, the nuclear charge (number of protons in the atomic nucleus) increases. There is a corresponding reduction in atomic radius as the increased nuclear charge draws the outer electrons closer to the nuclear core. In chemical bonding, nonmetals tend to gain electrons due to their higher nuclear charge, resulting in negatively charged ions.

The number of compounds formed by nonmetals is vast. The first 10 places in a "top 20" table of elements most frequently encountered in 895,501,834 compounds, as listed in the Chemical Abstracts Service register for November 2, 2021, were occupied by nonmetals. Hydrogen, carbon, oxygen, and nitrogen collectively appeared in most (80%) of compounds. Silicon, a metalloid, ranked 11th. The highest-rated metal, with an occurrence frequency of 0.14%, was iron, in 12th place. A few examples of nonmetal compounds are: boric acid, used in ceramic glazes; selenocysteine , the 21st amino acid of life; phosphorus sesquisulfide (P4S3), found in strike anywhere matches; and teflon n), used to create non-stick coatings for pans and other cookware.

Complications
Adding complexity to the chemistry of the nonmetals are anomalies occurring in the first row of each periodic table block; non-uniform periodic trends; higher oxidation states; multiple bond formation; and property overlaps with metals.

First row anomaly
Starting with hydrogen, the first row anomaly primarily arises from the electron configurations of the elements concerned. Hydrogen is particularly notable for its diverse bonding behaviors. It most commonly forms covalent bonds, but it can also lose its single electron in an aqueous solution, leaving behind a bare proton with tremendous polarizing power. Consequently, this proton can attach itself to the lone electron pair of an oxygen atom in a water molecule, laying the foundation for acid-base chemistry. Moreover, a hydrogen atom in a molecule can form a second, albeit weaker, bond with an atom or group of atoms in another molecule. Such bonding, "helps give snowflakes their hexagonal symmetry, binds DNA into a double helix; shapes the three-dimensional forms of proteins; and even raises water's boiling point high enough to make a decent cup of tea."

Hydrogen and helium, as well as boron through neon, have unusually small atomic radii. This phenomenon arises because the 1s and 2p subshells lack inner analogues (meaning there is no zero shell and no 1p subshell), and they therefore experience less electron-electron exchange interactions, unlike the 3p, 4p, and 5p subshells of heavier elements. As a result, ionization energies and electronegativities among these elements are higher than what periodic trends would otherwise suggest. The compact atomic radii of carbon, nitrogen, and oxygen facilitate the formation of double or triple bonds.

While it would normally be expected, on electron configuration consistency grounds, that hydrogen and helium would be placed atop the s-block elements, the significant first row anomaly shown by these two elements justifies alternative placements. Hydrogen is occasionally positioned above fluorine, in group 17, rather than above lithium in group 1. Helium is commonly placed above neon, in group 18, rather than above beryllium in group 2.

Secondary periodicity
An alternation in certain periodic trends, sometimes referred to as secondary periodicity, becomes evident when descending groups 13 to 15, and to a lesser extent, groups 16 and 17. Immediately after the first row of d-block metals, from scandium to zinc, the 3d electrons in the p-block elements—specifically, gallium (a metal), germanium, arsenic, selenium, and bromine—prove less effective at shielding the increasing positive nuclear charge.

The Soviet chemist gives two more tangible examples:
 * "The toxicity of some arsenic compounds, and the absence of this property in analogous compounds of phosphorus [P] and antimony [Sb]; and the ability of selenic acid [H2SeO4] to bring metallic gold [Au] into solution, and the absence of this property in sulfuric [H2SO4] and [H2TeO4] acids."

Higher oxidation states

 * Roman numerals such as III, V and VIII denote oxidation states

Some nonmetallic elements exhibit oxidation states that deviate from those predicted by the octet rule, which typically results in a valency of –3 in group 15, –2 in group 16, –1 in group 17, and 0 in group 18. Examples of such typical states can include compounds like ammonia N(III)H3, hydrogen sulfide(II) H2S, hydrogen fluoride(I) HF, and elemental xenon(0) Xe. Meanwhile, the maximum possible oxidation state increases from +5 in group 15, to +8 in group 18. The +5 oxidation state is observable from period 2 onward, in compounds such as nitric acid HN(V)O3 and phosphorus pentafluoride PCl5. Higher oxidation states in later groups emerge from period 3 onwards, as seen in sulfur hexafluoride SF6, iodine heptafluoride IF7, and xenon(VIII) tetroxide XeO4. For heavier nonmetals, their larger atomic radii and lower electronegativity values enable the formation of compounds with higher oxidation numbers, supporting higher bulk coordination numbers.

Multiple bond formation
Period 2 nonmetals, particularly carbon, nitrogen, and oxygen, show a propensity to form multiple bonds. The compounds formed by these elements often exhibit unique stoichiometries and structures, as seen in the various nitrogen oxides, which are not commonly found in elements from later periods.

Property overlaps
While certain elements have traditionally been classified as nonmetals and others as metals, some overlapping of properties occurs. Writing early in the twentieth century, by which time the era of modern chemistry had been well-established, Humphrey observed that:
 * ... these two groups, however, are not marked off perfectly sharply from each other; some nonmetals resemble metals in certain of their properties, and some metals approximate in some ways to the non-metals.

Examples of metal-like properties occurring in nonmetallic elements include:
 * Silicon has an electronegativity (1.9) comparable with metals such as cobalt (1.88), copper (1.9), nickel (1.91) and silver (1.93);
 * The electrical conductivity of graphite exceeds that of some metals;
 * Selenium can be drawn into a wire;
 * Radon is the most metallic of the noble gases and begins to show some cationic behavior, which is unusual for a nonmetal; and
 * In extreme conditions, just over half of nonmetallic elements can form homopolyatomic cations.

Examples of nonmetal-like properties occurring in metals are:
 * Tungsten displays some nonmetallic properties, sometimes being brittle, having a high electronegativity, and forming only anions in aqueous solution, and predominately acidic oxides.
 * Gold, the "king of metals" has the highest electrode potential among metals, suggesting a preference for gaining rather than losing electrons. Gold's ionization energy is one of the highest among metals, and its electron affinity and electronegativity are high, with the latter exceeding that of some nonmetals. It forms the Au– auride anion and exhibits a tendency to bond to itself, behaviors which are unexpected for metals. In aurides (MAu, where M = Li–Cs), gold's behavior is similar to that of a halogen. Gold has a large enough nuclear potential that the electrons have to be considered with relativistic effects included which changes some of the properties.

A relatively recent development involves certain compounds of heavier p-block elements, such as silicon, phosphorus, germanium, arsenic and antimony, exhibiting behaviors typically associated with transition metal complexes. This phenomenon is linked to a small energy gap between their filled and empty molecular orbitals, which are the regions in a molecule where electrons reside and where they can be available for chemical reactions. In such compounds, this closer energy alignment allows for unusual reactivity with small molecules like hydrogen (H2), ammonia (NH3), and ethylene (C2H4), a characteristic previously observed primarily in transition metal compounds. These reactions may open new avenues in catalytic applications.

Types
Nonmetal classification schemes vary widely, with some accommodating as few as two subtypes and others identifying up to seven. For example, the periodic table in the Encyclopaedia Britannica recognizes noble gases, halogens, and other nonmetals, and splits the elements commonly recognized as metalloids between "other metals" and "other nonmetals". On the other hand, seven of twelve color categories on the Royal Society of Chemistry periodic table include nonmetals.

Starting on the right side of the periodic table, three types of nonmetals can be recognized:

the relatively inert noble gases—helium, neon, argon, krypton, xenon, radon;

the notably reactive halogen nonmetals—fluorine, chlorine, bromine, iodine; and

the mixed reactivity "unclassified nonmetals", a set with no widely used collective name—hydrogen, carbon, nitrogen, oxygen, phosphorus, sulfur, selenium. The descriptive phrase unclassified nonmetals is used here for convenience.

The elements in a fourth set are sometimes recognized as nonmetals:

the generally unreactive metalloids, sometimes considered a third category distinct from metals and nonmetals—boron, silicon, germanium, arsenic, antimony, tellurium.

The boundaries between these types are not sharp. Carbon, phosphorus, selenium, and iodine border the metalloids and show some metallic character, as does hydrogen.

The greatest discrepancy between authors occurs in metalloid "frontier territory". Some consider metalloids distinct from both metals and nonmetals, while others classify them as nonmetals. Some categorize certain metalloids as metals (e.g., arsenic and antimony due to their similarities to heavy metals). Metalloids resemble the elements universally considered "nonmetals" in having relatively low densities, high electronegativity, and similar chemical behavior.

Noble gases
Six nonmetals are classified as noble gases: helium, neon, argon, krypton, xenon, and the radioactive radon. In conventional periodic tables they occupy the rightmost column. They are called noble gases due to their exceptionally low chemical reactivity.

These elements exhibit remarkably similar properties, characterized by their colorlessness, odorlessness, and nonflammability. Due to their closed outer electron shells, noble gases possess feeble interatomic forces of attraction, leading to exceptionally low melting and boiling points. As a consequence, they all exist as gases under standard conditions, even those with atomic masses surpassing many typically solid elements.

Chemically, the noble gases exhibit relatively high ionization energies, negligible or negative electron affinities, and high to very high electronegativities. The number of compounds formed by noble gases is in the hundreds and continues to expand, with most of these compounds involving the combination of oxygen or fluorine with either krypton, xenon, or radon.

Halogen nonmetals
While the halogen nonmetals are notably reactive and corrosive elements, they can also be found in everyday compounds like toothpaste (NaF); common table salt (NaCl); swimming pool disinfectant (NaBr); and food supplements (KI). The term "halogen" itself means "salt former".

Chemically, the halogen nonmetals exhibit high ionization energies, electron affinities, and electronegativity values, and are mostly relatively strong oxidizing agents. These characteristics contribute to their corrosive nature. All four elements tend to form primarily ionic compounds with metals, in contrast to the remaining nonmetals (except for oxygen) which tend to form primarily covalent compounds with metals. The highly reactive and strongly electronegative nature of the halogen nonmetals epitomizes nonmetallic character.

Unclassified nonmetals

Hydrogen behaves in some respects like a metallic element and in others like a nonmetal. Like a metallic element it can, for example, form a solvated cation in aqueous solution; it can substitute for alkali metals in compounds such as the chlorides (NaCl cf. HCl) and nitrates (KNO3 cf. HNO3), and in certain alkali .etal o i ein this way as a nonmetal. It attains this configuration by forming a covalent or ionic bond or, if it has initially given up its electron, by attaching itself to a lone pair of electrons.

Some or all of these nonmetals share several properties. Being generally less reactive than the halogens, most of them can occur naturally in the environment. They have significant roles in biology and geochemistry. Collectively, their physical and chemical characteristics can be described as "moderately non-metallic". Sometimes they have corrosive aspects. Carbon corrosion can occur in fuel cells. Untreated selenium in soils can lead to the formation of corrosive hydrogen selenide gas. Very different, when combined with metals, the unclassified nonmetals can form interstitial or refractory compounds due to their relatively small atomic radii and sufficiently low ionization energies. They also exhibit a tendency to bond to themselves, particularly in solid compounds. Additionally, diagonal periodic table relationships among these nonmetals mirror similar relationships among the metalloids.

Abundance
The abundance of elements in the universe results from nuclear physics processes like nucleosynthesis and radioactive decay.

The volatile noble gas nonmetal elements are less abundant in the atmosphere than expected based their overall abundance due to cosmic nucleosynthesis. Mechanisms to explain this difference is an important aspect of planetary science. Even within that challenge, the nonmetal element Xe is unexpectedly depleted. A possible explanation comes from theoretical models of the high pressures in the Earth's core suggest there may be around 1013 tons of xenon, in the form of stable XeFe3 and XeNi3 intermetallic compounds.

Five nonmetals—hydrogen, carbon, nitrogen, oxygen, and silicon—form the bulk of the directly observable structure of the Earth: about 73% of the crust, 93% of the biomass, 96% of the hydrosphere, and over 99% of the atmosphere, as shown in the accompanying table. Silicon and oxygen form highly stable tetrahedral structures, known as silicates. Here, "the powerful bond that unites the oxygen and silicon ions is the cement that holds the Earth's crust together."

In the biomass, the relative abundance of the first four nonmetals (and phosphorus, sulfur, and selenium marginally) is attributed to a combination of relatively small atomic size, and sufficient spare electrons. These two properties enable them to bind to one another and "some other elements, to produce a molecular soup sufficient to build a self-replicating system."

Extraction
Nine of the 23 nonmetallic elements are gases, or form compounds that are gases, and are extracted from natural gas or liquid air. These elements include hydrogen, helium, nitrogen, oxygen, neon, sulfur, argon, krypton, and xenon. For example, nitrogen and oxygen are extracted from air through fractional distillation of liquid air. This method capitalizes on their different boiling points to separate them efficiently. Sulfur was extracted using the Frasch process, which involved injecting superheated water into underground deposits to melt the sulfur, which is then pumped to the surface. This technique leveraged sulfur's low melting point relative to other geological materials. It is now obtained by reacting the hydrogen sulfide in natural gas, with oxygen. Water is formed, leaving the sulfur behind.

Nonmetallic elements are extracted from the following sources:

Gases (3): hydrogen, from methane; helium, from natural gas; sulfur, from hydrogen sulfide in natural gas

Liquids (9): nitrogen, oxygen, neon, argon, krypton and xenon from liquid air; chlorine, bromine and iodine from brine

Solids (12): boron, from borates; carbon occurs naturally as graphite; silicon, from silica; phosphorus, from phosphates; iodine, from sodium iodate; radon, as a decay product from uranium ores; fluorine, from fluorite; germanium, arsenic, selenium, antimony and tellurium, from sulfides.

Uses
Uses of nonmetals and non-metallic elements are broadly categorized as domestic, industrial, attenuative (lubricative, retarding, insulating or cooling), and agricultural

Many such elements have domestic and industrial applications. They have uses in household accoutrements; medicine and pharmaceuticals; and lasers and lighting. They are components of mineral acids; and prevalent in plug-in hybrid vehicles; and smartphones.

A significant number have attenuative and agricultural applications. They are used in lubricants; and flame retardants and fire extinguishers. They can serve as inert air replacements; and are used in cryogenics and refrigerants. Their significance extends to agriculture, through their use in fertilizers.

Additionally, a smaller number of nonmetals or nonmetallic elements find specialized uses in explosives; and welding gases.

Background
Around 340 BCE, in Book III of his treatise Meteorology, the ancient Greek philosopher Aristotle categorized substances found within the Earth into metals and "fossiles". The latter category included various minerals such as realgar, ochre, ruddle, sulfur, cinnabar, and other substances that he referred to as "stones which cannot be melted".

Until the Middle Ages the classification of minerals remained largely unchanged, albeit with varying terminology. In the fourteenth century, the English alchemist Richardus Anglicus expanded upon the classification of minerals in his work Correctorium Alchemiae. In this text, he proposed the existence of two primary types of minerals. The first category, which he referred to as "major minerals", included well-known metals such as gold, silver, copper, tin, lead, and iron. The second category, labeled "minor minerals", encompassed substances like salts, atramenta (iron sulfate), alums, vitriol, arsenic, orpiment, sulfur, and similar substances that were not metallic bodies.

The term "nonmetallic" dates back to at least the 16th century. In his 1566 medical treatise, French physician Loys de L'Aunay distinguished substances from plant sources based on whether they originated from metallic or non-metallic soils.

Later, the French chemist Nicolas Lémery discussed metallic and nonmetallic minerals in his work Universal Treatise on Simple Drugs, Arranged Alphabetically published in 1699. In his writings, he contemplated whether the substance "cadmia" belonged to either the first category, akin to cobaltum (cobaltite), or the second category, exemplified by what was then known as calamine—a mixed ore containing zinc carbonate and silicate.

Origin and use of the term
Just as the ancients distinguished metals from other minerals, a similar dichotomy developed as the modern idea of chemical elements emerged in the late 1700s. French chemist Antoine Lavoisier published the first modern list of chemical elements in his revolutionary 1789 Traité élémentaire de chimie. The elements were categorized into distinct groups, including gases, metallic substances, nonmetallic substances, and earths (heat-resistant oxides). Lavoisier's work gained widespread recognition and was republished in twenty-three editions across six languages within its first seventeen years, significantly advancing the understanding of chemistry in Europe and America.

The widespread adoption of the term "nonmetal" followed a complex process spanning nearly nine decades. In 1811, the Swedish chemist Berzelius introduced the term "metalloids" to describe nonmetallic elements, noting their ability to form negatively charged ions with oxygen in aqueous solutions. While Berzelius' terminology gained significant acceptance, it later faced criticism from some who found it counterintuitive, misapplied, or even invalid. In 1864, reports indicated that the term "metalloids" was still endorsed by leading authorities, but there were reservations about its appropriateness. The idea of designating elements like arsenic as metalloids had been considered. By as early as 1866, some authors began preferring the term "nonmetal" over "metalloid" to describe nonmetallic elements. In 1875, Kemshead observed that elements were categorized into two groups: non-metals (or metalloids) and metals. He noted that the term "non-metal", despite its compound nature, was more precise and had become universally accepted as the nomenclature of choice.

Suggested distinguishing criteria
From the mid-1700s, a variety of physical, chemical, and atomic properties have been suggested for distinguishing metals from nonmetals (or other bodies), as listed in the accompanying table. Some of the earliest recorded properties are the (high) density and (good) electrical conductivity of metals.

In 1809, the British chemist and inventor Humphry Davy made a groundbreaking discovery that reshaped the understanding of metals and nonmetals. When he isolated sodium and potassium, their low densities (floating on water!) contrasted with their metallic appearance, challenging the stereotype of metals as dense substances. Nevertheless, their classification as metals was firmly established by their distinct chemical properties.

One of the most commonly recognized properties used in this context is the temperature coefficient of resistivity, the effect of heating on electrical resistance and conductivity. As temperature rises, the conductivity of metals decreases while that of nonmetals increases. However, plutonium, carbon, arsenic, and antimony defy the norm. When plutonium (a metal) is heated within a temperature range of −175 to +125 °C its conductivity increases. Similarly, despite its common classification as a nonmetal, when carbon (as graphite) is heated it experiences a decrease in electrical conductivity. Arsenic and antimony, which are occasionally classified as nonmetals, show behavior similar to carbon, highlighting the complexity of the distinction between metals and nonmetals.

Kneen and colleagues proposed that the classification of nonmetals can be achieved by establishing a single criterion for metallicity. They acknowledged that various plausible classifications exist and emphasized that while these classifications may differ to some extent, they would generally agree on the categorization of nonmetals.

Emsley pointed out the complexity of this task, asserting that no single property alone can unequivocally assign elements to either the metal or nonmetal category. Furthermore, Jones emphasized that classification systems typically rely on more than two attributes to define distinct types.

Johnson distinguished between metals and nonmetals on the basis of their physical states, electrical conductivity, mechanical properties, and the acid-base nature of their oxides:
 * 1) gaseous elements are nonmetals (hydrogen, nitrogen, oxygen, fluorine, chlorine and the noble gases);
 * 2) liquids (mercury, bromine) are either metallic or nonmetallic: mercury, as a good conductor, is a metal; bromine, with its poor conductivity, is a nonmetal;
 * 3) solids are either ductile and malleable, hard and brittle, or soft and crumbly:
 * a. ductile and malleable elements are metals;
 * b. hard and brittle elements include boron, silicon and germanium, which are semiconductors and therefore not metals; and
 * c. soft and crumbly elements include carbon, phosphorus, sulfur, arsenic, antimony, tellurium and iodine, which have acidic oxides indicative of nonmetallic character.

Several authors have noted that nonmetals generally have low densities and high electronegativity. The accompanying table, using a threshold of 7 g/cm3 for density and 1.9 for electronegativity (revised Pauling), shows that all nonmetals have low density and high electronegativity. In contrast, all metals have either high density or low electronegativity (or both). Goldwhite and Spielman added that, "... lighter elements tend to be more electronegative than heavier ones." The average electronegativity for the elements in the table with densities less than 7 gm/cm3 (metals and nonmetals) is 1.97 compared to 1.66 for the metals having densities of more than 7 gm/cm3.

Some authors divide elements into metals, metalloids, and nonmetals, but Oderberg disagrees, arguing that by the principles of categorization, anything not classified as a metal should be considered a nonmetal.

Development of types

In 1844, Alphonse Dupasquier, a French doctor, pharmacist, and chemist, established a basic taxonomy of nonmetals to aid in their study. He wrote:

 * They will be divided into four groups or sections, as in the following:
 * Organogens—oxygen, nitrogen, hydrogen, carbon
 * Sulphuroids—sulfur, selenium, phosphorus
 * Chloroides—fluorine, chlorine, bromine, iodine
 * Boroids—boron, silicon.

Dupasquier's quartet parallels the modern nonmetal types. The organogens and sulphuroids are akin to the unclassified nonmetals. The chloroides were later called halogens. The boroids eventually evolved into the metalloids, with this classification beginning from as early as 1864. The then unknown noble gases were recognized as a distinct nonmetal group after being discovered in the late 1800s.

His taxonomy was noted for its natural basis. That said, it was a significant departure from other contemporary classifications, since it grouped together oxygen, nitrogen, hydrogen, and carbon.

In 1828 and 1859, the French chemist Dumas classified nonmetals as (1) hydrogen; (2) fluorine to iodine; (3) oxygen to sulfur; (4) nitrogen to arsenic; and (5) carbon, boron and silicon, thereby anticipating the vertical groupings of Mendeleev's 1871 periodic table. Dumas' five classes fall into modern groups 1, 17, 16, 15, and 14 to 13 respectively.

Comparison of selected properties
The two tables in this section list some of the properties of five types of elements (noble gases, halogen nonmetals, unclassified nonmetals, metalloids and, for comparison, metals) based on their most stable forms at standard temperature and pressure. The dashed lines around the columns for metalloids signify that the treatment of these elements as a distinct type can vary depending on the author, or classification scheme in use.

Physical properties by element type
Physical properties are listed in loose order of ease of their determination.

Chemical properties by element type
Chemical properties are listed from general characteristics to more specific details.

† Hydrogen can also form alloy-like hydrides

‡ The labels low, moderate, high, and very high are arbitrarily based on the value spans listed in the table

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title: Nonmetal