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"^[1] that have been in apparent conflict with one another since September 2007.

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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—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.^[2][3] 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.^[4]

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.^[4] 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.

References

1. ^ IUPAC Provisional Recommendations for the Nomenclature of Inorganic Chemistry (2004) (online draft of an updated version of the "Red Book" IR 3-6.2)
2. ^ Xuefang Wang; Lester Andrews; Sebastian Riedel; and Martin Kaupp (2007). "Mercury Is a Transition Metal: The First Experimental Evidence for HgF₄.". Angew. Chem. Int. Ed. 46 (44): 8371–8375. doi:10.1002/anie.200703710
3. ^ Elusive Hg(IV) species has been synthesized under cryogenic conditions (October 12, 2007) Accessed December 2, 2007
4. ^ ^{a b} "Post Transition Metal Chemistry Lecture 1" WebLearn - Oxford Campus, Department of Chemistry, public anonymous access, Michaelmas Term 2007, Prof. R.G. Egdell, Accessed December 2, 2007