Editing Metalloid (section)

===Judgment-based===
A metalloid is an element that possesses a preponderance of properties in between, or that are a mixture of, those of [[metal]]s and [[nonmetal]]s, and which is therefore hard to classify as either a [[metal]] or a [[nonmetal]]. This is a generic definition that draws on metalloid attributes consistently cited in the literature.{{refn|1=Definitions and extracts by different authors, illustrating aspects of the generic definition, follow:
*"In chemistry a metalloid is an element with properties intermediate between those of [[metal]]s and [[nonmetal]]s."<ref>[[#Cusack1987|Cusack 1987, p.&nbsp;360]]</ref>
*"Between the [[metal]]s and [[nonmetal]]s in the periodic table we find elements&nbsp;... [that] share some of the characteristic properties of both the [[metal]]s and [[Nonmetal|nonmetals]], making it difficult to place them in either of these two main categories"<ref>[[#Kelter2009|Kelter, Mosher & Scott 2009, p.&nbsp;268]]</ref>
*"Chemists sometimes use the name metalloid&nbsp;... for these elements which are difficult to classify one way or the other."<ref name="Hill 2000, p. 41">[[#Hill2000|Hill & Holman 2000, p.&nbsp;41]]</ref>
*"Because the traits distinguishing [[metal]]s and [[nonmetal]]s are qualitative in nature, some elements do not fall unambiguously in either category. These elements&nbsp;... are called metalloids&nbsp;..."<ref>[[#King1979|King 1979, p.&nbsp;13]]</ref>

More broadly, metalloids have been referred to as:
*"elements that&nbsp;... are somewhat of a cross between [[metal]]s and [[nonmetal]]s";<ref>[[#Moore2011|Moore 2011, p.&nbsp;81]]</ref> or
*"weird in-between elements".<ref>[[#Gray2010|Gray 2010]]</ref>|group=n}} Difficulty of categorisation is a key attribute. Most elements have a mixture of metallic and nonmetallic properties,<ref name=Hopkins>[[#Hopkins1956|Hopkins & Bailar 1956, p.&nbsp;458]]</ref> and can be classified according to which set of properties is more pronounced.<ref>[[#Glinka1965|Glinka 1965, p.&nbsp;77]]</ref>{{refn|1=[[Gold]], for example, has mixed properties but is still recognised as "king of [[metal]]s". Besides metallic behaviour (such as high electrical conductivity, and [[cation]] formation), gold shows nonmetallic behaviour:
*It has the [[table of standard electrode potentials|highest]] [http://www.chemguide.co.uk/physical/redoxeqia/introduction.html electrode potential]
*It has the third-highest [[ionization energy]] among the [[metal]]s (after [[zinc]] and [[mercury (element)|mercury]])
*It has the highest [[electron affinity]]
*Its [[electronegativity]] of 2.54 is highest among the [[metal]]s and exceeds that of some [[nonmetal]]s ([[hydrogen]] 2.2; [[phosphorus]] 2.19; and [[radon]] 2.2)
*It forms the Au<sup>−</sup> auride [[anion]], acting in this way like a [[halogen]]
*It sometimes has a tendency, known as "[[aurophilicity]]", to bond to itself.<ref>[[#Wiberg2001|Wiberg 2001, p.&nbsp;1279]]</ref>
On halogen character, see also Belpassi et al.,<ref>[[#Belpassi2006|Belpassi et al. 2006, pp.&nbsp;4543–44]]</ref> who conclude that in the aurides MAu (M = [[alkali metal|Li–Cs]]) gold "behaves as a halogen, intermediate between [[bromine|Br]] and [[iodine|I]]"; on aurophilicity, see also Schmidbaur and Schier.<ref>[[#Schmidbaur2008|Schmidbaur & Schier 2008, pp.&nbsp;1931–51]]</ref>|group=n}} Only the elements at or near the margins, lacking a sufficiently clear preponderance of either metallic or nonmetallic properties, are classified as metalloids.<ref>[[#TM1987|Tyler Miller 1987, p.&nbsp;59]]</ref>

[[Boron]], [[silicon]], [[germanium]], [[arsenic]], [[antimony]], and [[tellurium]] are commonly recognised as metalloids.<ref>[[#Goldsmith1982|Goldsmith 1982, p.&nbsp;526]]; [[#Kotz2009|Kotz, Treichel & Weaver 2009, p.&nbsp;62]]; [[#Bettelheim|Bettelheim et al. 2010, p.&nbsp;46]]</ref>{{refn|1=Mann et al.<ref name=Mann/> refer to these elements as "the recognized metalloids".|group=n}} Depending on the author, one or more from [[selenium]], [[polonium]], or [[astatine]] are sometimes added to the list.<ref>[[#Hawkes2001|Hawkes 2001, p.&nbsp;1686]]; [[#Segal1989|Segal 1989, p.&nbsp;965]]; [[#McMurray2009|McMurray & Fay 2009, p.&nbsp;767]]</ref> [[Boron]] sometimes is excluded, by itself, or with [[silicon]].<ref>[[#Bucat1983|Bucat 1983, p.&nbsp;26]]; [[#Brown2007|Brown c. 2007]]</ref> Sometimes [[tellurium]] is not regarded as a metalloid.<ref name="Swift1962,100">[[#Swift1962|Swift & Schaefer 1962, p.&nbsp;100]]</ref> The inclusion of [[antimony]], [[polonium]], and [[astatine]] as metalloids has been questioned.<ref>[[#Hawkes2001|Hawkes 2001, p.&nbsp;1686]]; [[#Hawkes2010|Hawkes 2010]]; [[#Holt2007|Holt, Rinehart & Wilson c. 2007]]</ref>

Other elements are occasionally classified as metalloids. These elements include<ref>[[#Dunstan1968|Dunstan 1968, pp.&nbsp;310, 409]]. Dunstan lists Be, Al, Ge (maybe), As, Se (maybe), Sn, Sb, Te, Pb, Bi, and Po as metalloids (pp.&nbsp;310, 323, 409, 419).</ref> [[hydrogen]],<ref>[[#Tilden1876|Tilden 1876, pp.&nbsp;172, 198–201]]; [[#Smith1994|Smith 1994, p.&nbsp;252]]; [[#Bodner1993|Bodner & Pardue 1993, p.&nbsp;354]]</ref> [[beryllium]],<ref>[[#Bassett1966|Bassett et al. 1966, p.&nbsp;127]]</ref> [[nitrogen]],<ref name=rausch>[[#Rausch1960|Rausch 1960]]</ref> [[phosphorus]],<ref>[[#Thayer1977|Thayer 1977, p.&nbsp;604]]; [[#Warren1981|Warren & Geballe 1981]]; [[#M&E|Masters & Ela 2008, p.&nbsp;190]]</ref> [[sulfur]],<ref>[[#Warren1981|Warren & Geballe 1981]]; [[#Chalmers1959|Chalmers 1959, p.&nbsp;72]]; [[#United1965|US Bureau of Naval Personnel 1965, p.&nbsp;26]]</ref> [[zinc]],<ref>[[#Siebring1967|Siebring 1967, p.&nbsp;513]]</ref> [[gallium]],<ref>[[#Wiberg2001|Wiberg 2001, p.&nbsp;282]]</ref> [[tin]], [[iodine]],<ref>[[#Rausch1960|Rausch 1960]]; [[#Friend1953|Friend 1953, p.&nbsp;68]]</ref> [[lead]],<ref>[[#Murray1928|Murray 1928, p.&nbsp;1295]]</ref> [[bismuth]],<ref name="Swift1962,100"/> and [[radon]].<ref>[[#Hampel&H1966|Hampel & Hawley 1966, p.&nbsp;950]]; [[#Stein1985|Stein 1985]]; [[#Stein1987|Stein 1987, pp.&nbsp;240, 247–48]]</ref> The term metalloid has also been used for elements that exhibit metallic [[Lustre (mineralogy)|lustre]] and [[Electrical resistivity and conductivity|electrical conductivity]], and that are [[amphoterism|amphoteric]], such as [[arsenic]], [[antimony]], [[vanadium]], [[chromium]], [[molybdenum]], [[tungsten]], [[tin]], [[lead]], and [[aluminium]].<ref>[[#Hatcher1949|Hatcher 1949, p.&nbsp;223]]; [[#Secrist|Secrist & Powers 1966, p.&nbsp;459]]</ref> The [[Post-transition metal#p-block metals|p-block metals]],<ref>[[#Taylor1960|Taylor 1960, p.&nbsp;614]]</ref> and nonmetals (such as carbon or nitrogen) that can form [[alloy]]s with metals<ref>[[#Considine1984|Considine & Considine 1984, p.&nbsp;568]]; [[#Cegielski1998|Cegielski 1998, p.&nbsp;147]]; [[#TheAmerican2005|''The American heritage science dictionary 2005'', p.&nbsp;397]]</ref> or modify their properties<ref>[[#Woodward1948|Woodward 1948, p.&nbsp;1]]</ref> have also occasionally been considered as metalloids.