Group 12: the zinc group

A full d subshell and two s electrons

Zinc is [Ar] 3d¹⁰ 4s², cadmium [Kr] 4d¹⁰ 5s² and mercury [Xe] 4f¹⁴ 5d¹⁰ 6s². The full d subshell stays untouched in their common compounds, so they behave more like main-group metals than typical transition metals. Zinc and cadmium form only Zn²⁺ and Cd²⁺, while mercury forms Hg²⁺ and also +1 compounds, in which two mercury atoms pair up as the Hg₂²⁺ ion.

With no gaps in the d subshell, zinc compounds such as zinc oxide and zinc sulfate are white, unlike the colorful compounds of iron, cobalt or copper.

Trends down the group

Group 12 has the lowest melting points in the d-block, and they fall down the group: zinc melts at 692.68 K, cadmium at 594.22 K and mercury at just 234.32 K, about −39 °C. Mercury boils at 629.88 K, but it gives off toxic vapor well below that, even at room temperature.

Density rises from 7.14 g/cm³ to 8.65 g/cm³ and 13.534 g/cm³, so steel and even lead float on liquid mercury. Mercury also has the highest first ionization energy of any metal, 10.438 eV; its 6s electrons are held so tightly that its atoms bond only weakly to each other, which is why it stays liquid.

Where you meet group 12

Zinc coats steel in galvanizing and keeps protecting it even where the coating is scratched. It is mixed with copper to make brass, zinc oxide is found in sunscreen, and zinc is an essential nutrient for the immune system. Cadmium was used in nickel–cadmium batteries and bright yellow paints, and mercury in thermometers and fluorescent lamps, but both are toxic, so these uses are being phased out.

Copernicium

Copernicium (112), named after Nicolaus Copernicus, has been made only a few atoms at a time. Its properties are predicted rather than measured. Experiments suggest it is very volatile, and some calculations predict it could be a liquid, or even a gas, at room temperature.