Footnote 2 There is nothing so special about metalloids that necessarily warrants placing them in a major class of their own. It is ironic that the term ‘metalloid’ was first popularly used to refer to nonmetals, boron and silicon notably so. While metalloids have a metallic appearance and are semiconductors, or are known in such forms, this is also the case for the nonmetals carbon (as graphite) phosphorus (as the black allotrope), selenium, and iodine. Yet plutonium, which is unambiguously a metal, increases its electrical conductivity when heated in the temperature range of around − 175 to +125 ☌ (Russell and Lee 2005, p. An objection can be raised that the metalloids arsenic and antimony, being semi-metals in the physics-based sense, reduce their electrical conductivity when heated, as do metals generally. A binary classification can facilitate the establishment of rules for determining bond types between metals and nonmetals (Roher 2001, pp. Ontologically speaking, anything not a metal is therefore a nonmetal, and this includes metalloids (Oderberg 2007, p. Some chemists and instructors may hesitate treating metalloids as nonmetals. 988) see also Dingle ( 2017) for a refreshing interpretation of the status of metalloids, as ‘poor non-metals’. Setting aside the confusion surrounding the metalloids, they are here treated as chemically weak nonmetals, consistent with Hawley’s Condensed Chemical Dictionary (Larrañaga et al. 849) rightly noted the non-metallic chemistry of the metalloids, and a few authors still do so. Some chemistry text-books (Choppin and Johnsen 1972, p. They are still widely regarded as such (Miller 2019 Wikipedia 2019b). With the emergence of the semiconductor industry in the 1950s, and the development of solid-state electronics from the early 1960s, metalloids came to be regarded as “in-between elements” (Rochow 1966 Chedd 1969). It has been known for over 120 years that metalloids have a predominately nonmetallic chemistry (Newth 1894 Friend 1914). The characteristics of the corrosive nonmetals and intermediate nonmetals are subsequently elaborated in this article, the latter at some length. This results in a balanced 6–5–6–6 distribution of the elements concerned. As the metals have been subdivided into four broad classes, so can the nonmetals be subdivided into like classes of noble gases corrosive nonmetals intermediate nonmetals and metalloids. And some or all of the metalloids may or may not be included in the applicable sections.Ī richer, complementary taxonomy is introduced in this article. Thus, in a textbook, there may be separate sections on hydrogen carbon nitrogen and phosphorus and oxygen, sulfur, and selenium. In Steudel’s Chemistry of the nonmetals (1977, preface)Īfter highlighting the halogens and the noble gases, authors have always found it difficult to treat the remaining nonmetals on a holistic rather than group-by-group basis. “The marvellous variety and infinite subtlety of the non-metallic elements, their compounds, structures and reactions, is not sufficiently acknowledged in the current teaching of chemistry.” The literature is sparse when it comes to holistic treatments of their chemistry. Wikipedia ( 2019a) records 15 different category names for these elements located between the transition metals and the metalloids, including ‘other metals’. In some respects, the frontier metals can be regarded as the forgotten metals. Being adjacent to the non-metals, their crystalline structures tend to show covalent or directional bonding effects, having generally greater complexity or fewer nearest neighbours than other metallic elements (Russell and Lee 2010, p. A minority are moderately electropositive (zinc, for example) (Kneen et al. Most of them, such as tin and bismuth, are chemically weak. The frontier metals, as a class, are adjacent to the dividing line between metals and nonmetals. A small number, such as zirconium, are more strongly electropositive several others are chemically very weak (or noble), like platinum, with these representing the noble metals. The transition metals are, for the most part, moderately to weakly electropositive in nature (Kneen et al. They are mostly strongly electropositive metals, with a few of the light actinoids (uranium to americium) being only moderately electropositive. The active metals are here considered to encompass groups 1–3, the lanthanoids and actinoids, and aluminium in group 3. Footnote 1 A fourth class, the noble metals, is a subset of the transition metals (MacKay et al. The metals can be divided into broad classes, as: active metals transition metals and frontier metals (Russell and Lee 2005, p. A few borderline elements are sometimes identified as metalloids. In general, the elements of the periodic table can be divided into metals and nonmetals.
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