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 (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.[n 1] Other sources may subtract from this list, add a varying number of other elements, or both.
This table shows which elements are included in each of 194 different lists of metalloids. A parenthesized symbol indicates an element whose inclusion in a particular metalloid list is qualified in some way by the author(s). The 'citations' rows show how many and what percentage of the authorities consider each element to be a metalloid, with qualified citations counted as one-half.
() Parenthesized symbols indicate elements whose inclusion in a particular metalloid list is qualified in some way by the author(s). It is counted as 0.5 citation.
There is an average of 7.15 elements per metalloid list.
Appearance frequency clusters
Clusters of elements and their appearance in the sources
Elements cited in the listed sources (as of August 2011; n = 194) have appearance frequencies that occur in clusters of comparable values. The diamonds in the graph mark the mean appearance frequency of each cluster.
Cluster 1 (93%): B, Si, Ge, As, Sb, Te
Cluster 2 (44%): Po, At
Cluster 3 (24%): Se
Cluster 4 (9%): C, Al
Cluster 5 (5%): Be, P, Bi
Cluster 6 (3%): Sn
Cluster 7 (1%): H, Ga, S, I, Pb, Fl, Mc, Lv, Ts
The resulting geometric trend line has the formula y = 199.47eβ0.7423x and an R2 value of 0.9962.[n 2]
Elements regarded as metalloids
The elements commonly classified as metalloids are boron, silicon, germanium, arsenic, antimony and tellurium.[n 3]
The status of polonium and astatine is not settled. Most authors recognise one or the other, or both, as metalloids; Herman, Hoffmann and Ashcroft, on the basis of relativistic modelling, predict astatine will be a monatomic metal.[n 4] One or more of carbon, aluminium, phosphorus, selenium, tin or bismuth, these being periodic table neighbours of the elements commonly classified as metalloids, are sometimes recognised as metalloids.[n 5]
Selenium, in particular, is commonly designated as a metalloid in environmental chemistry[n 6] on account of similarities in its aquatic chemistry with that of arsenic and antimony.[n 7] There are fewer references to beryllium, in spite of its periodic table position adjoining the dividing line between metals and nonmetals. Isolated references in the literature can also be found to the categorisation of other elements as metalloids. These elements include: hydrogen, nitrogen,[n 8] sulfur,[n 9] zinc,[n 10] gallium,[n 11] iodine,[n 12] lead,[n 13] and radon[n 14] (citations are for references other than those listed above).
Goldsmith RH 1982, 'Metalloids', Journal of Chemical Education, vol. 59, no. 6, pp. 526β527, doi:10.1021/ed059p526
Hawkes SJ 2001, 'Semimetallicity', Journal of Chemical Education, vol. 78, no. 12, pp. 1686β87, doi:10.1021/ed078p1686
βThe R2 value is a measure of how close a formula fits a set of data points. Values fall between 0.0 and 1.0, with those near 1.0 indicating a good fit.
Goldsmith RH 1982, 'Metalloids', Journal of Chemical Education, vol. 59, no. 6, pp. 526β7 (526), doi:10.1021/ed059p526
Mann JB, Meek TL & Allen LC 2000, 'Configuration energies of the main group elements', Journal of the American Chemical Society, vol. 122, no. 12, pp. 2780β3 (2783), doi:10.1021/ja992866e: Mann et al. refer to these elements as 'the recognized metalloids'.
Kotz JC, Treichel P & Weaver GC 2009, Chemistry and Chemical Reactivity, 7th ed., Brooks/Cole, Belmont, California, ISBN1439041318
Hawkes SJ 2010, 'Polonium and astatine are not semimetals', Journal of Chemical Education, vol. 87, no. 8, p. 783, doi:10.1021/ed100308w
Hermann A, Hoffmann R & Ashcroft NW 2013, 'Condensed Astatine: Monatomic and Metallic', Physical Review Letters, vol. 111, pp. 11604β1β11604-5, doi:10.1103/PhysRevLett.111.116404
Vernon RE 2013, 'Which Elements Are Metalloids?', Journal of Chemical Education, vol. 90, no. 12, pp. 1703β1707, doi:10.1021/ed3008457
Rochow EG 1966, The metalloids, DC Heath and Company, Boston, pp. 7β8
Cobb HM 2012, Dictionary of Metals, ASM International, Materials Park, OH, p. 145, ISBN9781615039784
Walker CH 2012, Organic Pollutants: An Ecotoxicological Perspective, 2nd ed., CRC Press, Boca Raton, FL, p. 163, ISBN9781420062588
Whiten K, Davis R, Peck L & Stanley G 2014, Chemistry, 10th ed., Brooks/Cole Cengage Learning, Belmont, CA, p. 134, ISBN9781133610663
βSelenium as a metalloid in environmental chemistry:
Meyer JS, Adams WJ, Brix KV, Luoma SM, Mount DR, Stubblefield WA & Wood CM (eds) 2005, Toxicity of dietborne metals to aquatic organisms, Proceedings from the Pellston Workshop on Toxicity of Dietborne Metals to Aquatic Organisms, 27 July β 1 August 2002, Fairmont Hot Springs, British Columbia, Canada, Society of Environmental Toxicology and Chemistry, Pensacola, Florida, p. 284, ISBN1880611708
Weiner ER 2013, Applications of Environmental Aquatic Chemistry: A Practical Guide, 3rd ed., CRC Press, Boca Raton, FL, p. 181, ISBN9781439853320
βSimilarities in the aquatic chemistry of selenium, arsenic, and antimony:
US Environmental Protection Agency 1988, Ambient aquatic life water quality criteria for antimony (III), draft, Office of Research and Development, Environmental Research Laboratories, Washington, p. 1
De Zuane J 1997, Handbook of drinking water quality, 2nd ed., John Wiley & Sons, New York, p. 93, ISBN047128789X
Uden PC 2005, 'Speciation of selenium,' in R Cornelis, J Caruso, H Crews & K Heumann (eds), Handbook of elemental speciation II: Species in the environment, food, medicine and occupational health, John Wiley & Sons, Chichester, pp. 346β65 (347β8), ISBN0470855983
Dev N 2008, 'Modelling selenium fate and transport in Great Salt Lake Wetlands' PhD dissertation, University of Utah, ProQuest, Ann Arbor, Michigan, pp. 2β3, ISBN054986542X
βNitrogen:
Rausch MD 1960, 'Cyclopentadienyl compounds of metals and metalloids', Journal of Chemical Education, vol. 37, no. 11, pp. 568β78, doi:10.1021/ed037p568
Friend JN 1953, Man and the chemical elements, 1st ed., Charles Scribner's Sons, New York, p. 68
Rausch MD 1960, 'Cyclopentadienyl compounds of metals and metalloids', Journal of Chemical Education, vol. 37, no. 11, pp. 568β78, doi:10.1021/ed037p568
βLead:
Murray JF 1928, 'Cable-sheath corrosion', Electrical World, vol. 92, Dec 29, pp. 1295β7 (1295)
Hampel CA & Hawley GG 1966, The encyclopedia of chemistry, 3rd ed., Van Nostrand Reinhold, New York,p. 950
Stein L 1985, 'New evidence that radon is a metalloid element: ion-exchange reactions of cationic radon', Journal of the Chemical Society, Chemical Communications, vol. 22, pp. 1631β2, doi:10.1039/C39850001631
Stein L 1987, 'Chemical properties of radon' in PK Hopke (ed.) 1987, Radon and its decay products: Occurrence, properties, and health effects, American Chemical Society, Washington DC, pp. 240β51 (240, 247β8), ISBN0841210152
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