Cadmium was discovered in 1817 simultaneously by Stromeyer and Hermann, both in Germany, as an impurity in zinc carbonate. It is a chemical element with the symbol Cd and atomic number 48. It is a soft and silvery white metal is chemically similar to the two other stable metals in group 12, zinc and mercury. Like zinc, it demonstrates oxidation state +2 in most of its compounds, and like mercury, it has a lower melting point than the transition metals in groups 3 through 11.
It occurs as a minor component in most zinc ores and is a byproduct of zinc production. It was used for a long time as a corrosion-resistant plating on steel, and Cd compounds are used as red, orange and yellow pigments, to color glass, and to stabilize plastic. It use is generally decreasing because it is toxic and nickel-cadmium batteries have been replaced with nickel-metal hydride and lithium-ion batteries. One of its few new uses is Cd telluride solar panels. Although It has no known biological function in higher organisms, a cadmium-dependent carbonic anhydrase has been found in marine diatoms.
It is a soft, malleable, ductile, silvery-white divalent metal. It is similar in many respects to zinc but forms complex compounds. Unlike most other metals, Cd is resistant to corrosion and is used as a protective plate on other metals. As a bulk metal, It is insoluble in water and is not flammable; however, in its powdered form it may burn and release toxic fumes.
Chemical Properties of Cadmium
- Cd and its congeners are not always considered transition metals, in that they do not have partly filled d or f electron shells in the elemental or common oxidation states.
- It burns in air to form brown amorphous cadmium oxide (CdO); the crystalline form of this compound is a dark red which changes color when heated, similar to zinc oxide. Hydrochloric acid, sulfuric acid, and nitric acid dissolve Cd by forming cadmium chloride (CdCl2), cadmium sulfate (CdSO4), or cadmium nitrate (Cd(NO3)2).
- The oxidation state +1 can be produced 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(I) chloride.