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Cadmium

Cadmium is a chemical element with the symbol Cd and atomic number 48. This soft bluish-white metal is chemically similar to Zinc and Mercury, and is toxic. This metal is banned by the RoHS directive.

Cadmium (Wikipedia)

Cadmium,  48Cd
Cadmium-crystal bar.jpg
General properties
Pronunciation/ˈkædmiəm/ (KAD-mee-əm)
Appearancesilvery bluish-gray metallic
Standard atomic weight (Ar, standard)112.414(4)
Cadmium in the periodic table
Hydrogen Helium
Lithium Beryllium Boron Carbon Nitrogen Oxygen Fluorine Neon
Sodium Magnesium Aluminium Silicon Phosphorus Sulfur Chlorine Argon
Potassium Calcium Scandium Titanium Vanadium Chromium Manganese Iron Cobalt Nickel Copper Zinc Gallium Germanium Arsenic Selenium Bromine Krypton
Rubidium Strontium Yttrium Zirconium Niobium Molybdenum Technetium Ruthenium Rhodium Palladium Silver Cadmium Indium Tin Antimony Tellurium Iodine Xenon
Caesium Barium Lanthanum Cerium Praseodymium Neodymium Promethium Samarium Europium Gadolinium Terbium Dysprosium Holmium Erbium Thulium Ytterbium Lutetium Hafnium Tantalum Tungsten Rhenium Osmium Iridium Platinum Gold Mercury (element) Thallium Lead Bismuth Polonium Astatine Radon
Francium Radium Actinium Thorium Protactinium Uranium Neptunium Plutonium Americium Curium Berkelium Californium Einsteinium Fermium Mendelevium Nobelium Lawrencium Rutherfordium Dubnium Seaborgium Bohrium Hassium Meitnerium Darmstadtium Roentgenium Copernicium Nihonium Flerovium Moscovium Livermorium Tennessine Oganesson
Zn

Cd

Hg
silvercadmiumindium
Atomic number (Z)48
Groupgroup 12
Periodperiod 5
Blockd-block
Element category  post-transition metal, alternatively considered a transition metal
Electron configuration[Kr] 4d10 5s2
Electrons per shell
2, 8, 18, 18, 2
Physical properties
Phase at STPsolid
Melting point594.22 K ​(321.07 °C, ​609.93 °F)
Boiling point1040 K ​(767 °C, ​1413 °F)
Density (near r.t.)8.65 g/cm3
when liquid (at m.p.)7.996 g/cm3
Heat of fusion6.21 kJ/mol
Heat of vaporization99.87 kJ/mol
Molar heat capacity26.020 J/(mol·K)
Vapor pressure
P (Pa) 1 10 100 1 k 10 k 100 k
at T (K) 530 583 654 745 867 1040
Atomic properties
Oxidation states−2, +1, +2 (a mildly basic oxide)
ElectronegativityPauling scale: 1.69
Ionization energies
  • 1st: 867.8 kJ/mol
  • 2nd: 1631.4 kJ/mol
  • 3rd: 3616 kJ/mol
Atomic radiusempirical: 151 pm
Covalent radius144±9 pm
Van der Waals radius158 pm
Color lines in a spectral range
Spectral lines of cadmium
Other properties
Crystal structurehexagonal close-packed (hcp)
Hexagonal close packed crystal structure for cadmium
Speed of sound thin rod2310 m/s (at 20 °C)
Thermal expansion30.8 µm/(m·K) (at 25 °C)
Thermal conductivity96.6 W/(m·K)
Electrical resistivity72.7 nΩ·m (at 22 °C)
Magnetic orderingdiamagnetic
Magnetic susceptibility−19.8·10−6 cm3/mol
Young's modulus50 GPa
Shear modulus19 GPa
Bulk modulus42 GPa
Poisson ratio0.30
Mohs hardness2.0
Brinell hardness203–220 MPa
CAS Number7440-43-9
History
Discovery and first isolationKarl Samuel Leberecht Hermann and Friedrich Stromeyer (1817)
Named byFriedrich Stromeyer (1817)
Main isotopes of cadmium
Iso­tope Abun­dance Half-life (t1/2) Decay mode Pro­duct
106Cd 1.25% stable
107Cd syn 6.5 h ε 107Ag
108Cd 0.89% stable
109Cd syn 462.6 d ε 109Ag
110Cd 12.47% stable
111Cd 12.80% stable
112Cd 24.11% stable
113Cd 12.23% 7.7×1015 y β 113In
113mCd syn 14.1 y β 113In
IT 113Cd
114Cd 28.75% stable
115Cd syn 53.46 h β 115In
116Cd 7.51% 3.1×1019 y ββ 116Sn
| references

Cadmium is a chemical element with symbol Cd and atomic number 48. This soft, bluish-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. 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. The average concentration of cadmium in Earth's crust is between 0.1 and 0.5 parts per million (ppm). It was discovered in 1817 simultaneously by Stromeyer and Hermann, both in Germany, as an impurity in zinc carbonate.

Cadmium occurs as a minor component in most zinc ores and is a byproduct of zinc production. 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. Cadmium use is generally decreasing because it is toxic (it is specifically listed in the European Restriction of Hazardous Substances) and nickel-cadmium batteries have been replaced with nickel-metal hydride and lithium-ion batteries. One of its few new uses is cadmium telluride solar panels.

Although cadmium has no known biological function in higher organisms, a cadmium-dependent carbonic anhydrase has been found in marine diatoms.

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