Condensed periodic table showing a typicalmetal–nonmetal dividing line.
Elements commonly recognised asmetalloids (boron, silicon, germanium, arsenic, antimony and tellurium) and those inconsistently recognised as such (polonium and astatine)
Metal-nonmetal dividing line (arbitrary): betweenLi and H,Be and B,Al and Si,Ge and As,Sb and Te,Po and At,Ts and Og
Thedividing line betweenmetals andnonmetals can be found, in varying configurations, on some representations of theperiodic 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]
The location and therefore usefulness of the line is debated. It cuts through themetalloids, elements that share properties between metals and nonmetals, in an arbitrary manner, since the transition between metallic and non-metallic properties among these elements is gradual.
This line has been called theamphoteric line,[2] themetal-nonmetal line,[3] themetalloid line,[4][5] thesemimetal line,[6] or thestaircase.[2][n 1] While it has also been called theZintl border[8] or theZintl line[9][10] these terms instead refer to avertical line sometimes drawn between groups 13 and 14. This particular line was named byLaves in 1941.[11] It differentiatesgroup 13 elements from those in and to the right ofgroup 14. The former generally combine with electropositive metals to makeintermetallic 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] textbookIntroduction 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]
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, however, 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]
The table below distinguishes the elements whose stable allotropes atstandard conditions are exclusively metallic (yellow) from those that are not. (Carbon and arsenic, which have both stable metallic and nonmetallic forms, are coloured according to their stable nonmetallic forms.)
MetallicNetwork covalentMolecularcovalentSingle atomsUnknownBackground color shows bonding of simple substances in theperiodic table. If there are several, the most stable allotrope is considered.
^Sacks[7] described the dividing line as, 'A jagged line, likeHadrian's Wall ... [separating] the metals from the rest, with a few "semimetals", metalloids—arsenic, selenium—straddling the wall.'
^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".
^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]
^Hinrichs 1869, p. 115. In his articleHinrichs 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."
^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."
King RB (ed.) 2005,Encyclopedia of inorganic chemistry, 2nd ed., John Wiley & Sons, Chichester, p. 6006,ISBN0-470-86078-2
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,ISBN1-56081-900-6
Kotz JC, Treichel P & Weaver GC 2005,Chemistry & chemical reactivity, 6th ed., Brooks/Cole, Belmont, CA,ISBN0-534-99766-X
Levy J 2011,The bedside book of chemistry, Pier 9, Millers Point, Sydney,ISBN978-1-74266-035-6
MacKay KM & MacKay RA 1989,Introduction to modern inorganic chemistry, 4th ed., Blackie, Glasgow,ISBN0-216-92534-7
Mendeléeff DI 1897,The principles of chemistry, vol. 1, 5th ed., trans. G Kamensky, AJ Greenaway (ed.), Longmans, Green & Co., London
Miles WD & Gould RF 1976,American chemists and chemical engineers, vol. 1, American Chemical Society, Washington
