The origin and usage of the term metalloid is convoluted. Its origin lies in attempts, dating from antiquity, to describe metals and to distinguish between typical and less typical forms. It was first applied to metals that floated on water (lithium, sodium and potassium), and then more popularly to nonmetals. Only recently, since the mid-20th century, has it been widely used to refer to elements with intermediate or borderline properties between metals and nonmetals.
Paracelsus (1493–1541), German-Swiss physician, iatrochemist, philosopher, astrologer and commentator as to the nature and properties of metals. He referred to zinc and bismuth as 'bastard' copper, and 'bastard' tin, respectively. Portrait by Quentin Massys
More sophisticated classification arrangements were proposed by Pseudo-Geber (in the Geber corpus, c. 1310), Paracelsus (De Natura Rerum libri nonem, 1525–6; and later works), Basil Valentine(Conclusiones, 1624), and Boerhaave(Elementa Chemiæ, 1733). They attempted to separate the more characteristic metals from substances having those characteristics to a lesser degree. Such substances included zinc, antimony, bismuth, stibnite, pyrite and galena. These were all then called semimetals or bastard metals.[4][5][6]
In 1735 Brandt proposed to make the presence or absence of malleability the principle of this classification. On that basis he separated mercury from the metals. The same view was adopted by Vogel (1755, Institutiones Chemiæ) and Buffon (1785, Histoire Naturelle des Minéraux). In the interim, Braun had observed the solidification of mercury by cold in 1759–60. This was confirmed by Hutchins and Cavendish in 1783.[7] The malleability of mercury then became known, and it was included amongst the metals.[4]
In 1789 Fourcroy[8] highlighted the weakness of this distinction between metals and semimetals. He said it was evident from the fact that
between the extreme malleability of gold and the singular fragility of arsenic, other metals presented only imperceptible gradations of this character, and because there was probably no greater difference between the malleability of gold and that of lead, which was considered to be a metal, than there was between lead and zinc, which was classed among semi-metals, while in the substances intermediate between zinc and arsenic the differences were slight.
Jöns Jacob Berzelius (1779–1848), Swedish chemist who popularized the use of the word metalloid to refer to nonmetallic chemical elements
In 1800, Pinkerton used the word metalloid, in its literal sense, to describe a mineral variety of pyroxene 'with metallic splendour.' [14]
In 1808, Erman and Simon suggested using the term metalloid to refer to the newly discovered elements sodium and potassium.[15] These elements were lighter than water and many chemists did not regard them as proper metals. Erman and Simon's proposal may have been made '[in] an attempt to revive this old distinction between metals and substances resembling metals'.[16] Their suggestion was ignored by the chemical community.[17]
In 1811, Berzelius referred to nonmetallic elements as metalloids,[17][18] in reference to their ability to form oxyanions.[19][20] A common oxyanion of sulfur, for example, is the sulfate ion SO2− 4. Many metals can do the same. Chromium, for instance, can form the chromate ion CrO2− 4. Berzelius' terminology was widely adopted[17] although it was subsequently regarded by some commentators as counterintuitive,[20] misapplied,[12] incorrect[21] or invalid.[22] In 1825, in a revised German edition of his Textbook of Chemistry,[23][24] Berzelius subdivided the metalloids into three classes. These were: constantly gaseous 'gazolyta' (hydrogen, nitrogen, oxygen); real metalloids (sulfur, phosphorus, carbon, boron, silicon); and salt-forming 'halogenia' (fluorine, chlorine, bromine, iodine).[25]
In 1844, Jackson gave the meaning of 'metalloid' as 'like metals, but wanting some of their properties.'[26] In 1845, in A dictionary of science, literature and art, Berzelius' classification of the elementary bodies was represented as: I. gazolytes; II. halogens; III. metalloids ('resemble the metals in certain aspects, but are in others widely different'); and IV. metals.[27]
In 1864, calling nonmetals 'metalloids' was still sanctioned 'by the best authorities'[28] even though this did not always seem appropriate. The greater propriety of applying the word metalloid to other elements, such as arsenic, had been considered.[28]
By as early as 1866 some authors were instead using the term nonmetal, rather than metalloid, to refer to nonmetallic elements.[29] In 1875, Kemshead observed that the elements had been subdivided into two classes—'non-metals or metalloids, and metals.' He added that '[t]he former term, although not so convenient, because a compound word, is more correct, and is now universally employed.'[30]
In 1876, Tilden protested against, 'the [still] too common though illogical practice of giving the name metalloid to such bodies as oxygen, chlorine or fluorine'. He instead divided the elements into ('basigenic') true metals, metalloids ('imperfect metals') and ('oxigenic') nonmetals.[31]
As late as 1888, classifying the elements into metals, metalloids, and nonmetals, rather than metals and metalloids, was still regarded as peculiar and potentially confusing.[32]
Beach, writing in 1911, explained it this way:[33]
Metalloid (Gr. "metal-like"), in chemistry, any nonmetallic element. There are 13, namely, sulfur, phosphorus, fluorin[e], chlorin[e], iodine, bromine, silicon, boron, carbon, nitrogen, hydrogen, oxygen, and selenium. The distinction between the metalloids and the metals is slight. The former, excepting selenium and phosphorus, do not have a "metallic" lustre; they are poorer conductors of heat and electricity, are generally not reflectors of light and not electropositive; that is, no metalloid fails of all these tests. The term seems to have been introduced into modern usage instead of nonmetals for the very reason that there is no hard and fast line between metals and nonmetals, so that "metal-like" or "resembling metals" is a better description of the class than the purely negative "nonmetals". Originally it was applied to the nonmetals which are solid at ordinary temperature.
In or around 1917, the Missouri Board of Pharmacy wrote[34] that:
A metal may be said to differ from a metalloid [that is, a nonmetal] in being an excellent conductor of heat and electricity, in reflecting light more or less powerfully and in being electropositive. A metalloid may possess one or more of these characters, but not all of them... Iodine is most commonly given as an example of a metalloid because of its metallic appearance.
During the 1920s the two meanings of the word metalloid appeared to be undergoing a transition in popularity. Writing in A Dictionary of Chemical Terms, Couch[35] defined 'metalloid' as an old, obsolescent term for 'nonmetal.' [n 2] In contrast, Webster's New International Dictionary noted that use of the term metalloid to refer to nonmetals was the norm. Its application to elements resembling the typical metals in some way only, such as arsenic, antimony and tellurium, was recorded merely on a 'sometimes' basis.[36]
Use of the term metalloid subsequently underwent a period of great flux up to 1940. Consensus as to its application to intermediate or borderline elements did not occur until the ensuing years, between 1940 and 1960.[17]
In 1947, Pauling included a reference to metalloids in his classic[37] and influential[38] textbook, General chemistry: An introduction to descriptive chemistry and modern chemical theory. He described them as 'elements with intermediate properties... occupy[ing] a diagonal region [on the periodic table], which includes boron, silicon, germanium, arsenic, antimony, tellurium, and polonium.'[39]
In 1959 the International Union of Pure and Applied Chemistry (IUPAC) recommended that '[t]he word metalloid should not be used to denote nonmetals'[40] although it was still being used in this sense (around that time) by, for example, the French.[41]
1960–present
In 1969 the classic[42] and authoritative[43]Hackh's Chemical Dictionary included entries for both 'metalloid' and 'semimetal'. The latter term was described as obsolete.[44]
In 1970 IUPAC recommended abandoning the term metalloid because of its continuing inconsistent use in different languages. They suggested using the terms metal, semimetal and nonmetal instead.[41][45] Despite this recommendation, use of the term 'metalloid' increased dramatically.[17]Google Ngram Viewer showed a fourfold increase in the use of the word 'metalloid' (as compared to 'semimetal') in the American English corpus from 1972 to 1983. There was a sixfold increase in the British English corpus from 1976 to 1983. As at 2011, the difference in usage across the English corpus was around 4:1 in favour of 'metalloid'.[46]
The most recent IUPAC publications on chemical nomenclature (the "Red Book", 2005) [47] and terminology (the "Gold Book", 2006–) [48] do not include any recommendations as to the usage or non-usage of the terms metalloid or semimetal.[n 3]
Use of the term semimetal, rather than metalloid, has recently been discouraged. This is because the former term 'has a well defined and quite distinct meaning in physics'.[49] In physics, a semimetal is an element or a compound in which the valence band marginally (rather than substantially) overlaps the conduction band. This results in only a small number of effective charge carriers.[50][51] Thus, the densities of charge carriers in the elemental semimetals carbon (as graphite, in the direction of its planes), arsenic, antimony and bismuth are 3×1018 cm−3, 2 ×1020 cm−3, 5×1019 cm−3 and 3×1017 cm−3 respectively.[52] In contrast, the room-temperature concentration of electrons in metals usually exceeds 1022 cm−3.[53]
References to 'metalloid' as being outdated have also been described as 'nonsense' noting that 'it accurately describes these weird in-between elements'.[54]
Notes
↑ In its first seventeen years, Lavoisier's work was republished in twenty-three editions and six languages, and carried his 'new chemistry' across Europe and America.[13]
↑ Couch also commented[35] that there was, 'no sharp line of demarcation between metals and nonmetals as many of the latter class possess some metallic properties' [italics added].
↑ The "Gold Book" [48] contains one reference to semimetals in the physics-based sense (see 'semiconductor-metal transition') and one reference in the chemistry based sense (see 'organometallic compounds'). The latter entry notes that 'traditional metals and semi-metals' can form such compounds, as can 'boron, silicon, arsenic and selenium'.
↑ Erman and Simon (1808) "3. Dritter Bericht des Hrn. Prof. Erman und des Geh. Oberbauraths Simon über ihre gemeinschaftlichen Versuche" (Third report of Prof. Erman and State Architect Simon on their joint experiments), Annalen der Physik, 28 (3): 347-367. After studying the new metallic elements that Humphry Davy had isolated, physicist Paul Erman and architect Paul Ludwig Simon concluded that potassium and sodium didn't conform to the traditional criteria of metals and therefore should be classified as "metalloids". From p. 347: "Hierin liegt aber eine sehr grosse Schwierigkeit, weil veilleicht keine der bekannten Substanzen einen so hohen Grad von Oxydabilität besitzt, als diese beiden Metalloide, wie man sie wohl an füglichsten vor der Hand nennen sollte." (However, here lies a very great difficulty because perhaps none of the known substances possess so high a degree of oxidizability as these two metalloids, as one should perhaps call those [that are] most conveniently available.)
↑ Grant 1969, pp.422, 604: 'metalloid.—(1) having the physical properties of metals and the chemical properties of nonmetals, e.g., As. (2) a nonmetal (incorrect usage)... semimetal.—an element midway in properties between metals and nonmetals, as arsenic (obsolete).'
Antimony is a chemical element with the symbol Sb (from Latin: stibium) and atomic number 51. A lustrous gray metalloid, it is found in nature mainly as the sulfide mineral stibnite (Sb2S3). Antimony compounds have been known since ancient times and were powdered for use as medicine and cosmetics, often known by the Arabic name kohl. The earliest known description of the metal in the West was written in 1540 by Vannoccio Biringuccio.
The periodic table, also known as the periodic table of the (chemical) elements, is a rows and columns arrangement of the chemical elements. It is widely used in chemistry, physics, and other sciences, and is generally seen as an icon of chemistry. It is a graphic formulation of the periodic law, which states that the properties of the chemical elements exhibit an approximate periodic dependence on their atomic numbers. The table is divided into four roughly rectangular areas called blocks. The rows of the table are called periods, and the columns are called groups. Elements from the same group of the periodic table show similar chemical characteristics. Trends run through the periodic table, with nonmetallic character increasing from left to right across a period, and from down to up across a group, and metallic character increasing in the opposite direction. The underlying reason for these trends is electron configurations of atoms. The periodic table exclusively lists electrically neutral atoms that have an equal number of positively charged protons and negatively charged electrons and puts isotopes at the same place. Other atoms, like nuclides and isotopes, are graphically collected in other tables like the tables of nuclides.
A metalloid is a type of chemical element which has a preponderance of properties in between, or that are a mixture of, those of metals and nonmetals. There is no standard definition of a metalloid and no complete agreement on which elements are metalloids. Despite the lack of specificity, the term remains in use in the literature of chemistry.
In chemistry, a nonmetal is a chemical element that generally lacks a predominance of metallic properties; they range from colorless gases to shiny solids. The electrons in nonmetals behave differently from those in metals; with some exceptions, the electrons in nonmetals are fixed in place, resulting in nonmetals usually being poor conductors of heat and electricity, and brittle or crumbly when solid. The electrons in metals are generally free-moving and this is why metals are good conductors and most are easily flattened into sheets and drawn into wires. Nonmetal atoms tend to attract electrons in chemical reactions and to form acidic compounds.
A noble metal is ordinarily regarded as a metallic chemical element that is generally resistant to corrosion and is usually found in nature in its raw form. Gold, platinum, and the other platinum group metals are most often so classified. Silver, copper and mercury are sometimes included as noble metals, however less often as each of these usually occurs in nature combined with sulfur.
A pnictogen is any of the chemical elements in group 15 of the periodic table. Group 15 is also known as the nitrogen group or nitrogen family. Group 15 consists of the elements nitrogen (N), phosphorus (P), arsenic (As), antimony (Sb), bismuth (Bi), and moscovium (Mc).
A semimetal is a material with a very small overlap between the bottom of the conduction band and the top of the valence band. According to electronic band theory, solids can be classified as insulators, semiconductors, semimetals, or metals. In insulators and semiconductors the filled valence band is separated from an empty conduction band by a band gap. For insulators, the magnitude of the band gap is larger than that of a semiconductor. Because of the slight overlap between the conduction and valence bands, semimetals have no band gap and a negligible density of states at the Fermi level. A metal, by contrast, has an appreciable density of states at the Fermi level because the conduction band is partially filled.
In chemistry, a trivial name is a nonsystematic name for a chemical substance. That is, the name is not recognized according to the rules of any formal system of chemical nomenclature such as IUPAC inorganic or IUPAC organic nomenclature. A trivial name is not a formal name and is usually a common name.
A chemical nomenclature is a set of rules to generate systematic names for chemical compounds. The nomenclature used most frequently worldwide is the one created and developed by the International Union of Pure and Applied Chemistry (IUPAC).
A chemical substance is a form of matter having constant chemical composition and characteristic properties. Some references add that chemical substance cannot be separated into its constituent elements by physical separation methods, i.e., without breaking chemical bonds. Chemical substances can be simple substances, chemical compounds, or alloys.
There are currently 118 known chemical elements exhibiting many different physical and chemical properties. Amongst this diversity, scientists have found it useful to use names for various sets of elements, that illustrate similar properties, or their trends of properties. Many of these sets are formally recognized by the standards body IUPAC.
This is a list of 194 sources that list elements classified as metalloids. The sources are listed in chronological order. Lists of metalloids differ since there is no rigorous widely accepted definition of metalloid. Individual lists share common ground, with variations occurring at the margins. The elements most often regarded as metalloids are boron, silicon, germanium, arsenic, antimony and tellurium. Other sources may subtract from this list, add a varying number of other elements, or both.
The chemical elements can be broadly divided into metals, metalloids and nonmetals according to their shared physical and chemical properties. All metals have a shiny appearance ; are good conductors of heat and electricity; form alloys with other metals; and have at least one basic oxide. Metalloids are metallic-looking brittle solids that are either semiconductors or exist in semiconducting forms, and have amphoteric or weakly acidic oxides. Typical nonmetals have a dull, coloured or colourless appearance; are brittle when solid; are poor conductors of heat and electricity; and have acidic oxides. Most or some elements in each category share a range of other properties; a few elements have properties that are either anomalous given their category, or otherwise extraordinary.
The dividing line between metals and nonmetals can be found, in varying configurations, on some representations of the periodic table of the elements. Elements to the lower left of the line generally display increasing metallic behaviour; elements to the upper right display increasing nonmetallic behaviour. When presented as a regular stair-step, elements with the highest critical temperature for their groups lie just below the line.
The metallic elements in the periodic table located between the transition metals and the chemically weak nonmetallic metalloids have received many names in the literature, such as post-transition metals, poor metals, other metals, p-block metals and chemically weak metals; none have been recommended by IUPAC. The most common name, post-transition metals, is generally used in this article. Depending on where the adjacent sets of transition metals and metalloids are judged to begin and end, there are at least five competing proposals for which elements to count as post-transition metals: the three most common contain six, ten and thirteen elements, respectively. All proposals include gallium, indium, tin, thallium, lead, and bismuth.
Heavy metals are generally defined as metals with relatively high densities, atomic weights, or atomic numbers. The criteria used, and whether metalloids are included, vary depending on the author and context. In metallurgy, for example, a heavy metal may be defined on the basis of density, whereas in physics the distinguishing criterion might be atomic number, while a chemist would likely be more concerned with chemical behaviour. More specific definitions have been published, but none of these have been widely accepted. The definitions surveyed in this article encompass up to 96 out of the 118 known chemical elements; only mercury, lead and bismuth meet all of them. Despite this lack of agreement, the term is widely used in science. A density of more than 5 g/cm3 is sometimes quoted as a commonly used criterion and is used in the body of this article.
Nonmetals show more variability in their properties than do metals. Metalloids are included here since they behave predominately as chemically weak nonmetals.
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