Included Elements
A first IUPAC definition states "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.
Read more about this topic: Post-transition Metals
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