Dividing line between metals and nonmetals

The dividing line between metals and nonmetals can be found, in varying configurations, on some representations of the periodic table of the elements (see mini-example, right). 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 (Li, Be, Al, Ge, Sb, Po) lie just below the line.[1]

1 2 12 13 14 15 16 17 18
Condensed periodic table showing a typical metal–nonmetal dividing line.
  Elements commonly recognised as metalloids (boron, silicon, germanium, arsenic, antimony and tellurium) and those inconsistently recognised as such (polonium and astatine)
  Metal-nonmetal dividing line (arbitrary): between Li and H, Be and B, Al and Si, Ge and As, Sb and Te, Po and At, Ts and Og


This line has been called the amphoteric line,[2] the metal-nonmetal line,[3] the metalloid line,[4][5] the semimetal line,[6] or the staircase.[2][n 1] It is also erroneously referred to as the Zintl border[8] or the Zintl line.[9][10] The last two terms instead refer to a vertical line sometimes drawn between groups 13 and 14. This particular line was christened by Laves in 1941.[11] It differentiates group 13 elements from those in and to the right of group 14. The former generally combine with electropositive metals to make intermetallic compounds whereas the latter usually form salt-like compounds.[12]


References to a dividing line between metals and nonmetals appear in the literature as far back as at least 1869.[13] In 1891, Walker published a periodic 'tabulation' with a diagonal straight line drawn between the metals and the nonmetals.[14] In 1906, Alexander Smith published a periodic table with a zigzag line separating the nonmetals from the rest of elements, in his highly influential[15] textbook Introduction to General Inorganic Chemistry.[16] In 1923, Horace G. Deming, an American chemist, published short (Mendeleev style) and medium (18-column) form periodic tables.[17] Each one had a regular stepped line separating metals from nonmetals. Merck and Company prepared a handout form of Deming's 18-column table, in 1928, which was widely circulated in American schools. By the 1930s Deming's table was appearing in handbooks and encyclopaedias of chemistry. It was also distributed for many years by the Sargent-Welch Scientific Company.[18][19][20]

Double line variant

A dividing line between metals and nonmetals is sometimes replaced by two dividing lines. One line separates metals and metalloids; the other metalloids and nonmetals.[21][22]


Mendeleev wrote that, 'It is ... impossible to draw a strict line of demarcation between metals and nonmetals, there being many intermediate substances'.[23][n 2][n 3] Several other sources note confusion or ambiguity as to the location of the dividing line;[26][27] suggest its apparent arbitrariness[28] provides grounds for refuting its validity;[29] and comment as to its misleading, contentious or approximate nature.[30][31][32] Deming himself noted that the line could not be drawn very accurately.[33]


  1. ^ Sacks[7] described the dividing line as, 'A jagged line, like Hadrian's Wall ... [separating] the metals from the rest, with a few "semimetals," metalloids—arsenic, selenium—straddling the wall.'
  2. ^ In the context of Mendeleev's observation, Glinka[24] adds that: 'In classing an element as a metal or a nonmetal we only indicate which of its properties—metallic or nonmetallic—are more pronounced in it'.
  3. ^ Mendeleev regarded tellurium as such an intermediate substance: '... it is a bad conductor of heat and electricity, and in this respect, as in many others, it forms a transition from the metals to the nonmetals.'[25]


  1. ^ Horvath 1973, p. 336
  2. ^ a b Levy 2001, p. 158
  3. ^ Tarendash 2001, p. 78
  4. ^ Thompson 1999
  5. ^ DiSalvo 2000, p. 1800
  6. ^ Whitley 2009
  7. ^ Sacks 2001, pp. 191, 194
  8. ^ King 2005, p. 6006
  9. ^ Herchenroeder & Gschneidner 1988
  10. ^ De Graef & McHenry 2007, p. 34
  11. ^ Kniep 1996, p. xix
  12. ^ Nordell & Miller 1999, p. 579
  13. ^ Hinrichs 1869, p. 115. In his article Hinrichs included a periodic table, organized by atomic weight, but this did not show a metal-nonmetal dividing line. Rather, he wrote that, '... elements of like properties or their compounds of like properties, form groups bounded by simple lines. Thus a line drawn through C, As, Te, separates the elements, having metallic lustre from those not having such lustre. The gaseous elements form a small group by themselves, the condensible [sic] chlorine forming the boundary ... So also the boundary lines for other properties may be drawn.'
  14. ^ Walker 1891, p. 252
  15. ^ Miles & Gould 1976, p. 444: 'His "Introduction to General Inorganic Chemistry," 1906, was one of the most important textbooks in the field during the first quarter of the twentieth century.'
  16. ^ Smith 1906, pp. 408, 410
  17. ^ Deming 1923, pp. 160, 165
  18. ^ Abraham, Coshow & Fix, W 1994, p. 3
  19. ^ Emsley 1985, p. 36
  20. ^ Fluck 1988, p. 432
  21. ^ Brown & Holme 2006, p. 57
  22. ^ Swenson 2005
  23. ^ Mendeléeff 1897, p. 23
  24. ^ Glinka 1959, p. 77
  25. ^ Mendeléeff 1897, p. 274
  26. ^ MacKay & MacKay 1989, p. 24
  27. ^ Norman 1997, p. 31
  28. ^ Whitten, Davis & Peck 2003, p. 1140
  29. ^ Roher 2001, pp. 4–6
  30. ^ Hawkes 2001, p. 1686
  31. ^ Kotz, Treichel & Weaver 2005, pp. 79–80
  32. ^ Housecroft & Constable 2006, p. 322
  33. ^ Deming 1923, p. 381


  • Abraham M, Coshow, D & Fix, W 1994, Periodicity: A source book module, version 1.0. Chemsource, Inc., New York, viewed 26 Aug 11
  • Brown L & Holme T 2006, Chemistry for engineering students, Thomson Brooks/Cole, Belmont CA, ISBN 0-495-01718-3
  • De Graef M & McHenry ME 2007, Structure of materials: an introduction to crystallography, diffraction and symmetry, Cambridge University Press, Cambridge, ISBN 0-521-65151-4
  • Deming HG 1923, General chemistry: An elementary survey, John Wiley & Sons, New York
  • DiSalvo FJ 2000, 'Challenges and opportunities in solid-state chemistry', Pure and Applied Chemistry, vol. 72, no. 10, pp. 1799–1807, doi:10.1351/pac200072101799
  • Emsley J, 1985 'Mendeleyev's dream table', New Scientist, 7 March, pp. 32–36
  • Fluck E 1988, 'New notations in the period table', Pure and Applied Chemistry, vol. 60, no. 3, pp. 431–436
  • Glinka N 1959, General chemistry, Foreign Languages Publishing House, Moscow
  • Hawkes SJ 2001, 'Semimetallicity', Journal of Chemical Education, vol. 78, no. 12, pp. 1686–87, doi:10.1021/ed078p1686
  • Herchenroeder JW & Gschneidner KA 1988, 'Stable, metastable and nonexistent allotropes', Journal of Phase Equilibria, vol. 9, no. 1, pp. 2–12, doi:10.1007/BF02877443
  • Hinrichs GD 1869, 'On the classification and the atomic weights of the so-called chemical elements, with particular reference to Stas's determinations', Proceedings of the American Association for the Advancement of Science, vol. 18, pp. 112–124
  • Horvath 1973, 'Critical temperature of elements and the periodic system', Journal of Chemical Education, vol. 50, no. 5, pp. 335–336, doi:10.1021/ed050p335
  • Housecroft CE & Constable EC 2006, Chemistry, 3rd ed., Pearson Education, Harlow, England, ISBN 0-13-127567-4
  • King RB (ed.) 2005, Encyclopedia of inorganic chemistry, 2nd ed., John Wiley & Sons, Chichester, p. 6006, ISBN 0-470-86078-2
  • Kniep R 1996, 'Eduard Zintl: His life and scholarly work', in SM Kauzlarich (ed.), Chemistry, structure and bonding of Zintl phases and ions, VCH, New York, pp. xvii–xxx, ISBN 1-56081-900-6
  • Kotz JC, Treichel P & Weaver GC 2005, Chemistry & chemical reactivity, 6th ed., Brooks/Cole, Belmont, CA, ISBN 0-534-99766-X
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  • Mendeléeff DI 1897, The principles of chemistry, vol. 1, 5th ed., trans. G Kamensky, AJ Greenaway (ed.), Longmans, Green & Co., London
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  • Thompson R 1999, 'Re: What is the metalloid line and where is it located on the Periodic Table?', MadSci Network
  • Walker J 1891, 'On the periodic tabulation of the elements', The Chemical News, vol. LXIII, no. 1644, May 29, pp. 251–253
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External links

Lists of metalloids

This is a list of sources that each list metalloids: elements classified as metalloids. The sources are listed in chronological order. Lists of metalloids differ since there is no rigorous definition of metalloid (or its occasional alias, 'semi-metal'). 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. Wikipedia generally categorises these six as metalloids, with the addition of astatine. Other sources may subtract from this list or add a varying number of other elements.


A metalloid is a type of chemical element which has properties in between, or that are a mixture of, those of metals and nonmetals. There is neither a standard definition of a metalloid nor complete agreement on the elements appropriately classified as such. Despite the lack of specificity, the term remains in use in the literature of chemistry.

The six commonly recognised metalloids are boron, silicon, germanium, arsenic, antimony, and tellurium. Five elements are less frequently so classified: carbon, aluminium, selenium, polonium, and astatine. On a standard periodic table, all eleven elements are located in a diagonal region of the p-block extending from boron at the upper left to astatine at lower right. Some periodic tables include a dividing line between metals and nonmetals and the metalloids may be found close to this line.

Typical metalloids have a metallic appearance, but they are brittle and only fair conductors of electricity. Chemically, they behave mostly as nonmetals. They can form alloys with metals. Most of their other physical properties and chemical properties are intermediate in nature. Metalloids are usually too brittle to have any structural uses. They and their compounds are used in alloys, biological agents, catalysts, flame retardants, glasses, optical storage and optoelectronics, pyrotechnics, semiconductors, and electronics.

The electrical properties of silicon and germanium enabled the establishment of the semiconductor industry in the 1950s and the development of solid-state electronics from the early 1960s.The term metalloid originally referred to nonmetals. Its more recent meaning, as a category of elements with intermediate or hybrid properties, became widespread in 1940–1960. Metalloids are sometimes called semimetals, a practice that has been discouraged, as the term semimetal has a different meaning in physics than in chemistry. In physics, it specifically refers to the electronic band structure of a substance.


In chemistry, a nonmetal (or non-metal) is a chemical element that mostly lacks the characteristics of a metal. Physically, a nonmetal tends to have a relatively low melting point, boiling point, and density. A nonmetal is typically brittle when solid and usually has poor thermal conductivity and electrical conductivity. Chemically, nonmetals tend to have relatively high ionization energy, electron affinity, and electronegativity. They gain or share electrons when they react with other elements and chemical compounds. Seventeen elements are generally classified as nonmetals: most are gases (hydrogen, helium, nitrogen, oxygen, fluorine, neon, chlorine, argon, krypton, xenon and radon); one is a liquid (bromine); and a few are solids (carbon, phosphorus, sulfur, selenium, and iodine). Metalloids such as boron, silicon, and germanium are sometimes counted as nonmetals.

The nonmetals are divided into two categories reflecting their relative propensity to form chemical compounds: reactive nonmetals and noble gases. The reactive nonmetals vary in their nonmetallic character. The less electronegative of them, such as carbon and sulfur, mostly have weak to moderately strong nonmetallic properties and tend to form covalent compounds with metals. The more electronegative of the reactive nonmetals, such as oxygen and fluorine, are characterised by stronger nonmetallic properties and a tendency to form predominantly ionic compounds with metals. The noble gases are distinguished by their great reluctance to form compounds with other elements.

The distinction between categories is not absolute. Boundary overlaps, including with the metalloids, occur as outlying elements in each category show or begin to show less-distinct, hybrid-like, or atypical properties.

Although five times more elements are metals than nonmetals, two of the nonmetals—hydrogen and helium—make up over 99 percent of the observable universe. Another nonmetal, oxygen, makes up almost half of the Earth's crust, oceans, and atmosphere. Living organisms are composed almost entirely of nonmetals: hydrogen, oxygen, carbon, and nitrogen. Nonmetals form many more compounds than metals.

Periodic table

The periodic table, also known as the periodic table of elements, is a tabular display of the chemical elements, which are arranged by atomic number, electron configuration, and recurring chemical properties. The structure of the table shows periodic trends. The seven rows of the table, called periods, generally have metals on the left and non-metals on the right. The columns, called groups, contain elements with similar chemical behaviours. Six groups have accepted names as well as assigned numbers: for example, group 17 elements are the halogens; and group 18 are the noble gases. Also displayed are four simple rectangular areas or blocks associated with the filling of different atomic orbitals.

The organization of the periodic table can be used to derive relationships between the various element properties, and also to predict chemical properties and behaviours of undiscovered or newly synthesized elements. Russian chemist Dmitri Mendeleev published the first recognizable periodic table in 1869, developed mainly to illustrate periodic trends of the then-known elements. He also predicted some properties of unidentified elements that were expected to fill gaps within the table. Most of his forecasts proved to be correct. Mendeleev's idea has been slowly expanded and refined with the discovery or synthesis of further new elements and the development of new theoretical models to explain chemical behaviour. The modern periodic table now provides a useful framework for analyzing chemical reactions, and continues to be widely used in chemistry, nuclear physics and other sciences.

The elements from atomic numbers 1 (hydrogen) through 118 (oganesson) have been discovered or synthesized, completing seven full rows of the periodic table. The first 94 elements all occur naturally, though some are found only in trace amounts and a few were discovered in nature only after having first been synthesized. Elements 95 to 118 have only been synthesized in laboratories or nuclear reactors. The synthesis of elements having higher atomic numbers is currently being pursued: these elements would begin an eighth row, and theoretical work has been done to suggest possible candidates for this extension. Numerous synthetic radionuclides of naturally occurring elements have also been produced in laboratories.

Post-transition metal

Post-transition metals are a set of metallic elements in the periodic table located between the transition metals to their left, and the metalloids to their right. Depending on where these adjacent groups are judged to begin and end, there are at least five competing proposals for which elements to include: the three most common contain six, ten and thirteen elements, respectively (see image). All proposals include gallium, indium, tin, thallium, lead, and bismuth.

Physically, post-transition metals are soft (or brittle), have poor mechanical strength, and have melting points lower than those of the transition metals. Being close to the metal-nonmetal border, their crystalline structures tend to show covalent or directional bonding effects, having generally greater complexity or fewer nearest neighbours than other metallic elements.

Chemically, they are characterised—to varying degrees—by covalent bonding tendencies, acid-base amphoterism and the formation of anionic species such as aluminates, stannates, and bismuthates (in the case of aluminium, tin, and bismuth, respectively). They can also form Zintl phases (half-metallic compounds formed between highly electropositive metals and moderately electronegative metals or metalloids).

The name is universally used, but not officially sanctioned by any organization such as the IUPAC. The origin of the term is unclear: one early use was in 1940 in a chemistry text. Alternate names for this group are B-subgroup metals, other metals, and p-block metals; and at least eleven other labels.

Periodic table forms
Sets of elements
See also

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