Editing Metalloid (section)

===Location===
Metalloids lie on either side of the [[dividing line between metals and nonmetals]]. This can be found, in varying configurations, on some [[periodic table]]s. Elements to the lower left of the line generally display increasing metallic behaviour; elements to the upper right display increasing nonmetallic behaviour.<ref name="Hamm 1969, p.653"/> When presented as a regular stairstep, elements with the highest [[critical point (thermodynamics)|critical temperature]] for their groups (Li, Be, Al, Ge, Sb, Po) lie just below the line.<ref>[[#Horvath1973|Horvath 1973, p.&nbsp;336]]</ref>

The diagonal positioning of the metalloids represents an exception to the observation that elements with similar properties tend to occur in vertical [[group (periodic table)|groups]].<ref name="Gray91">[[#Gray2009|Gray 2009, p.&nbsp;9]]</ref> A related effect can be seen in other [[diagonal relationship|diagonal similarities]] between some elements and their lower right neighbours, specifically lithium-magnesium, beryllium-aluminium, and boron-silicon. Rayner-Canham<ref name="Rayner2011">[[#Rayner2011|Rayner-Canham 2011]]</ref> has argued that these similarities extend to carbon-phosphorus, nitrogen-sulfur, and into three [[d-block]] series.

This exception arises due to competing horizontal and vertical trends in the [[nuclear charge]]. Going along a [[period (periodic table)|period]], the [[effective nuclear charge|nuclear charge]] increases with [[atomic number]] as do the number of electrons. The additional pull on outer electrons as nuclear charge increases generally outweighs the screening effect of having more electrons. With some irregularities, atoms therefore become smaller, ionization energy increases, and there is a gradual change in character, across a period, from strongly metallic, to weakly metallic, to weakly nonmetallic, to strongly nonmetallic elements.<ref>[[#Booth1972|Booth & Bloom 1972, p.&nbsp;426]]; [[#Cox2004|Cox 2004, pp.&nbsp;17, 18, 27–28]]; [[#Silberberg2006|Silberberg 2006, pp.&nbsp;305–13]]</ref> Going down a [[main-group element|main group]], the effect of increasing nuclear charge is generally outweighed by the effect of additional electrons being further away from the nucleus. Atoms generally become larger, ionization energy falls, and metallic character increases.<ref>[[#Cox2004|Cox 2004, pp.&nbsp;17–18, 27–28]]; [[#Silberberg2006|Silberberg 2006, pp.&nbsp;305–13]]</ref> The net effect is that the location of the metal–nonmetal transition zone shifts to the right in going down a group,<ref name=Gray91/> and analogous diagonal similarities are seen elsewhere in the periodic table, as noted.<ref>[[#Rodgers|Rodgers 2011, pp.&nbsp;232–33; 240–41]]</ref>