Poor metal

In chemistry, the trivial name poor metals is sometimes applied to the metallic elements in the p-block of the periodic table. Their melting and boiling points are generally lower than those of the transition metals and their electronegativity values higher, and they are also softer. Being close to the metal-nonmetal border, their crystalline structures tend to show covalent effects, having generally greater complexity or fewer nearest neighbours than other metallic elements. The poor metals are distinguished from the metalloids by their significantly higher electrical conductivity values and, for elements in the same periodic table row, greater densities.

Applicable elements

"Poor metals" is not a rigorous IUPAC-approved term, but the grouping is generally taken to include aluminium, gallium, indium, thallium, tin, lead, bismuth and polonium.^[1] Occasionally germanium and antimony are also included, although these are usually considered to be metalloids. Elements 113, 114, 115, and 116, which are currently allocated the names ununtrium, flerovium, ununpentium, and livermorium, would likely exhibit properties characteristic of poor metals; sufficient quantities of them have not yet been synthesized to enable an examination of their chemical properties.

Post-transition metals

The term post-transition metal is generally used to describe the category of metallic elements in periods 4–6 of the periodic table, to the right of the transition elements.^[2][3] Since this description excludes aluminium, a period 3 metal,^{[n 1]} the post-transition elements thereby form a subset of the poor metals.

Which elements are counted as post-transition metals depends, in periodic table terms, on where the transition metals end.^{[n 2]} In the 1950s, most inorganic chemistry textbooks defined transition elements as finishing at group 10—nickel, palladium and platinum, therefore excluding group 11—copper, silver and gold, and group 12—zinc, cadmium and mercury.^[8] An examination of textbooks and monographs in 2003 revealed that the transition metals ended at either group 11 or group 12 with roughly equal frequency.^[8] Occasionally aluminium, germanium or antimony are also included as post-transition metals, although the latter two are usually considered to be metalloids.^[9]

Notes

References