Post-transition metal

Post-transition metals in the periodic table
	12	13	14	15	16
Group →
↓ Period
3		Alumin­ium 13 Al	Sili­con 14 Si
4	Zinc 30 Zn	Gallium 31 Ga	Germa­nium 32 Ge	Arsenic 33 As
5	Cad­mium 48 Cd	Indium 49 In	Tin 50 Sn	Anti­mony 51 Sb	Tellur­ium 52 Te
6	Mer­cury 80 Hg	Thallium 81 Tl	Lead 82 Pb	Bis­muth 83 Bi	Polo­nium 84 Po
Transition metal   Post-transition metal   Metalloid
Atomic number color shows state at STP: black=Solid, green=Liquid

In chemistry, the term post-transition metal is used to describe the category of metallic elements to the right of the transition elements on the periodic table. Which elements should be included in the post-transition metals is still widely disputed.

Included elements

A first IUPAC definition states "[T]he elements of groups 3–12 are the d-block elements. These elements are also commonly referred to as the transition elements, though the elements of group 12 are not always included". Depending on the inclusion of group 12 as a transition metal, the post-transition metals may or may not include the group 12 elements—zinc, cadmium, and mercury. An examination of textbooks and monographs in 2003 revealed that the group 12 elements are included and excluded with roughly equal frequency.

A second IUPAC definition for transition metals states "An element whose atom has an incomplete d sub-shell, or which can give rise to cations with an incomplete d sub-shell." Based on this definition one could argue group 12 should be split with mercury and copernicium as transition metals, and zinc and cadmium as post-transition metals. Of relevance is the synthesis of mercury(IV) fluoride, which establishes mercury as a transition metal. Copernicium is predicted to have an electron configuration similar to mercury, predicting it as a transition metal as well.

Occasionally germanium, antimony, or both are also included, although these are usually considered to be metalloids.

In the 1950s, most inorganic chemistry textbooks defined transition elements as excluding the coinage metals, group 11—copper, silver, and gold in addition to group 12.

Poor metals

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 that of the transition metals and their electronegativity higher, and they are also softer. They are distinguished from the metalloids by their significantly higher boiling points and conductivity in the same period.^{citation needed}

"Poor metals" is not a rigorous IUPAC-approved nomenclature, but the grouping is generally taken to include aluminium, gallium, indium, tin, thallium, lead, bismuth and polonium. Occasionally germanium and antimony are also included, although these are usually considered to be metalloids or "semi-metals". 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 examine their chemical properties.^{citation needed}

External links

• Patent-Invent – Poor Metals Quick Facts
• Royal Armouries – Poor Metals