Cadmium

Cadmium is a chemical element with the symbol Cd and atomic number 48. The soft, bluish-white metal is chemically similar to the two other metals zinc and mercury. Similar to zinc it prefers oxidation state +2 in most of its compounds and similar to mercury it shows a low melting point compared to transition metals. Cadmium is not considered a transition metal, in that it does not have partly filled d or f electron shells in the elemental or common oxidation states and is a relatively abundant element.

Cadmium occurs as a minor component in most zinc ores and therefore is a by-product of zinc production. Cadmium was for a long time used as pigment and for corrosion resistant plating on steel. Cadmium compounds were used to stabilize plastic. With the exception of its use in cadmium telluride solar panels, the use of cadmium is generally decreasing in all other applications. This decrease is due to the high toxicity of cadmium and the associated health concerns. Although cadmium is toxic, one enzyme, a carbonic anhydrase with cadmium as reactive centre has been discovered.

Characteristics

Cadmium is a soft, malleable, ductile, bluish-white bivalent metal. It is similar in many respects to zinc but forms more complex compounds. The most common oxidation state of cadmium is +2, though rare examples of +1 can be found. Cadmium burns in air to form brown amorphous cadmium oxide (CdO). The crystalline form of the same compound is dark red and changes color when heated, similar to zinc oxide. Hydrochloric acid, sulphuric acid and nitric acid dissolve cadmium by forming cadmium chloride (CdCl2) cadmium sulphate (CdSO4) or cadmium nitrate (Cd(NO3)2). The oxidation state +1 can be reached by dissolving cadmium in a mixture of cadmium chloride and aluminium chloride, forming the Cd22+ cation, which is similar to the Hg22+ cation in mercury chloride.

Value

The base value of each unit of ranges between 5 and 10Ð per unit, with up to 4 units being found at any one time.

Presence on Mars: Common