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Other authors have relied on, for example, atomic conductance{{refn|1=Atomic conductance is the electrical conductivity of one mole of a substance. It is equal to electrical conductivity divided by molar volume.<ref name="Hill 2000, p. 41"/>|group=n}}<ref>[[#Hill2000|Hill & Holman 2000, p. 160]]. They characterise metalloids (in part) on the basis that they are "poor conductors of electricity with atomic conductance usually less than 10<sup>−3</sup> but greater than 10<sup>−5</sup> ohm<sup>−1</sup> cm<sup>−4</sup>".</ref> or [[coordination number#Usage in quasicrystal, liquid and other disordered systems|bulk coordination number]].<ref>[[#Bond2005|Bond 2005, p. 3]]: "One criterion for distinguishing semi-metals from true metals under normal conditions is that the [[coordination number#Usage in quasicrystal, liquid and other disordered systems|bulk coordination number]] of the former is never greater than eight, while for metals it is usually twelve (or more, if for the body-centred cubic structure one counts next-nearest neighbours as well)."</ref>
Jones, writing on the role of classification in science, observed that "[classes] are usually defined by more than two attributes".<ref>[[#Jones2010|Jones 2010, p. 169]]</ref> Masterton and Slowinski<ref>[[#Masterton1977|Masterton & Slowinski 1977, p. 160]] list B, Si, Ge, As, Sb, and Te as metalloids, and comment that Po and At are ordinarily classified as metalloids but add that this is arbitrary as so little is known about them.</ref> used three criteria to describe the six elements commonly recognised as metalloids: metalloids have [[ionization energy|ionization energies]] around 200 kcal/mol (837 kJ/mol) and electronegativity values close to 2.0. They also said that metalloids are typically semiconductors, though antimony and arsenic (semimetals from a physics perspective) have electrical conductivities approaching those of metals. Selenium and polonium are suspected as not in this scheme, while astatine's status is uncertain.{{refn|1=Selenium has an ionization energy (IE) of 225 kcal/mol (941 kJ/mol) and is sometimes described as a semiconductor. It has a relatively high 2.55 electronegativity (EN). Polonium has an IE of 194 kcal/mol (812 kJ/mol) and a 2.0 EN, but has a metallic band structure.<ref>[[#Kraig2004|Kraig, Roundy & Cohen 2004, p. 412]]; [[#Alloul2010|Alloul 2010, p. 83]]</ref> Astatine has an IE of 215 kJ/mol (899 kJ/mol) and an EN of 2.2.<ref>[[#Vernon|Vernon 2013, p. 1704]]</ref> Its electronic band structure is not known with any certainty.|group=n}}
In this context, Vernon proposed that a metalloid is a chemical element that, in its standard state, has (a) the electronic band structure of a semiconductor or a semimetal; and (b) an intermediate first ionization potential "(say 750−1,000 kJ/mol)"; and (c) an intermediate electronegativity (1.9–2.2).<ref>[[#Vernon|Vernon 2013, p. 1703]]</ref>
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