Post-transition metal

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. There are two IUPAC definitions of "transition element" that have been in apparent conflict with one another since September 2007.

According to the first definition, transition metals are elements in group 3 through group 11. In this case, post-transition metals include all of group 12&mdash;zinc, cadmium, mercury, and ununbium.

According to the second definition, transition elements either have an incomplete d-subshell or have the ability to form an incomplete d-subshell. In 2007, mercury(IV) fluoride was synthesized. This compound contains a mercury atom with an incomplete d-subshell, and ununbium is predicted to have the capacity to form a similar electronic configuration. In this case, post-transition metals include only zinc and cadmium within group 12. This situation is illustrated by the element boxes colored gray to the right.

Finally, there is a common non-IUPAC definition that equates transition metals with the d-block. In this case, all of group 12 would consist of transition metals. This definition is not used at the university level.

Antimony (atomic number=51, placed to the right of Sn on the table) is arguably either a metalloid or a metal and is often considered to be a post-transition metal. Aluminum (atomic number=13, placed above Ga) is neither a transition nor a post-transition metal because it has no d-subshell and is located above the transition elements in the table. Also, the categorization of all "Uu" elements is speculative and not based on experimental data.