Group 12 element

A group 12 element is one in the series of elements in group 12 (IUPAC style) in the periodic table, consisting of transition metals which are zinc (Zn), cadmium (Cd), mercury (Hg), and ununbium (Uub). When compared with other groups of transitional metals, this group of elements has both relatively low melting points and boiling points, and both decrease down the group; the most obvious example is mercury, which is in liquid state under normal room temperature.

The reason for this group having a liquid metal (mercury) and other low-melting elements has partly to do with the electron configuration of mercury, and also with relativistic effects ^[1]. The electron configuration of mercury is [Kr] 4d¹⁰ 4f¹⁴ 5s² 5p⁶ 5d¹⁰ 6s². The last shell labeled 6s is completely full, and is noticeably closer to the nucleus than what would be expected if relativistic effects were not taken into account. The positive charge of the nucleus is so high that some of the electrons in the atoms are moving very fast—fast (for the sake of argument considering electrons as particles not as waves) enough that special relativity has to be taken into account in predicting their movement. Their mass increases and the size and energies of the s-orbital decreases as a function of velocity.

The combination of these two factors results in a rather tightly bound outer shell of electrons for mercury. Hence, mercury cannot form particularly strong metal-metal bonds. The result is an element which is liquid at room temperature. In fact because of its inert outer electrons mercury vapor behaves like a noble gas and has been called pseudohelium. This is in contrast with gold and thallium, which are beside mercury on the periodic table but are solids.

Group 12 elements are also relatively resistant to corrosion, and can be used to cover baser metals like iron galvanizing (using zinc) or electroplating (using cadmium).

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