The known isotopes of cadmium range in atomic mass from 94.950 u ( 95Cd) to 131.946 u ( 132Cd). All of the remaining radioactive isotopes have half-lives of less than 2.5 hours, and the majority have half-lives of less than 5 minutes. Among the isotopes that do not occur naturally, the most long-lived are 109Cd with a half-life of 462.6 days, and 115Cd with a half-life of 53.46 hours. At least three isotopes – 110Cd, 111Cd, and 112Cd – are stable. The other three are 106Cd, 108Cd (both double electron capture), and 114Cd (double beta decay) only lower limits on these half-lives have been determined. The two natural radioactive isotopes are 113Cd ( beta decay, half-life is 7.7 ×10 15 y) and 116Cd (two-neutrino double beta decay, half-life is 2.9 ×10 19 y). Two of them are radioactive, and three are expected to decay but have not done so under laboratory conditions. Naturally occurring cadmium is composed of eight isotopes. Isotopes The cadmium-113 total cross section clearly showing the cadmium cut-off The structures of many cadmium complexes with nucleobases, amino acids, and vitamins have been determined. The oxidation state +1 can be produced by dissolving cadmium in a mixture of cadmium chloride and aluminium chloride, forming the Cd 2 2+ cation, which is similar to the Hg 2 2+ cation in mercury(I) chloride. Hydrochloric acid, sulfuric acid, and nitric acid dissolve cadmium by forming cadmium chloride (CdCl 2), cadmium sulfate (CdSO 4), or cadmium nitrate (Cd(NO 3) 2). Cadmium 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. Cadmium 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. Chemical properties Īlthough cadmium usually has an oxidation state of +2, it also exists in the +1 state. As a bulk metal, cadmium is insoluble in water and is not flammable however, in its powdered form it may burn and release toxic fumes. Unlike most other metals, cadmium is resistant to corrosion and is used as a protective plate on other metals. It is similar in many respects to zinc but forms complex compounds. One of its few new uses is in cadmium telluride solar panels.Īlthough cadmium has no known biological function in higher organisms, a cadmium-dependent carbonic anhydrase has been found in marine diatoms.Ĭharacteristics Physical properties Ĭadmium is a soft, malleable, ductile, silvery-white divalent metal. Cadmium use is generally decreasing because it is toxic (it is specifically listed in the European Restriction of Hazardous Substances Directive ) and nickel-cadmium batteries have been replaced with nickel-metal hydride and lithium-ion batteries. Cadmium was used for a long time as a corrosion-resistant plating on steel, and cadmium compounds are used as red, orange, and yellow pigments, to color glass, and to stabilize plastic. It was discovered in 1817 simultaneously by Stromeyer and Hermann, both in Germany, as an impurity in zinc carbonate.Ĭadmium occurs as a minor component in most zinc ores and is a byproduct of zinc production. The average concentration of cadmium in Earth's crust is between 0.1 and 0.5 parts per million (ppm). Cadmium and its congeners in group 12 are often not considered transition metals, in that they do not have partly filled d or f electron shells in the elemental or common oxidation states. 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. This soft, silvery-white metal is chemically similar to the two other stable metals in group 12, zinc and mercury. Cadmium is a chemical element with the symbol Cd and atomic number 48.
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