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| General |
| Name, Symbol, Number |
cadmium, Cd, 48 |
| Chemical series |
transition metals |
| Group, Period, Block |
12, 5, d |
| Appearance |
silvery gray metallic
 |
| Atomic mass |
112.411(8) g/mol |
| Electron configuration |
[Kr] 4d10 5s2 |
| Electrons per shell |
2, 8, 18, 18, 2 |
| Physical properties |
| Phase |
solid |
| Density (near r.t.) |
8.65 g/cm³ |
| Liquid density at m.p. |
7.996 g/cm³ |
| Melting point |
594.22 K
(321.07 °C, 609.93 °F) |
| Boiling point |
1040 K
(767 °C, 1413 °F) |
| Heat of fusion |
6.21 kJ/mol |
| Heat of vaporization |
99.87 kJ/mol |
| Heat capacity |
(25 °C) 26.020 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 |
| Crystal structure |
hexagonal |
| Oxidation states |
2
(mildly basic oxide) |
| Electronegativity |
1.69 (Pauling scale) |
| Ionization energies |
1st: 867.8 kJ/mol |
| 2nd: 1631.4 kJ/mol |
| 3rd: 3616 kJ/mol |
| Atomic radius |
155 pm |
| Atomic radius (calc.) |
161 pm |
| Covalent radius |
148 pm |
| Van der Waals radius |
158 pm |
| Miscellaneous |
| Magnetic ordering |
no data |
| Electrical resistivity |
(22 °C) 72.7 nΩ·m |
| Thermal conductivity |
(300 K) 96.6 W/(m·K) |
| Thermal expansion |
(25 °C) 30.8 µm/(m·K) |
| Speed of sound (thin rod) |
(20 °C) 2310 m/s |
| Young's modulus |
50 GPa |
| Shear modulus |
19 GPa |
| Bulk modulus |
42 GPa |
| Poisson ratio |
0.30 |
| Mohs hardness |
2.0 |
| Brinell hardness |
203 MPa |
| CAS registry number |
7440-43-9 |
| Notable isotopes |
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| References |
Cadmium is a chemical element in the periodic table that has the symbol Cd and atomic number 48. A relatively rare, soft, bluish-white, toxic transition metal, cadmium occurs with zinc ores and is used largely in batteries.
Notable characteristics
Cadmium is a soft, malleable, ductile, bluish-white bivalent metal which can be easily cut with a knife. It is similar in many respects to zinc but lends itself to more complex compounds.
The most common oxidation state of cadmium is +2, though rare examples of +1 can be found.
Applications
About three-fourths of cadmium is used in batteries (especially Ni-Cd batteries) and most of the remaining one-fourth is used mainly for pigments, coatings and plating, and as stabilizers for plastics. Other uses;
History
Cadmium (Latin cadmia, Greek kadmeia meaning "calamine") was discovered in Germany in 1817 by Friedrich Strohmeyer. Strohmeyer found the new element within an impurity in zinc carbonate (calamine) and for 100 years Germany remained the only important producer of the metal. The metal was named after the Latin word for calamine since the metal was found in this zinc compound. Strohmeyer noted that some impure samples of calamine changed color when heated but pure calamine did not.
Even though cadmium and its compounds are highly toxic, the British Pharmaceutical Codex from 1907 states that cadmium iodide was used as a medicine to treat "enlarged joints, scrofulous glands, and chilblains".
In 1927, the International Conference on Weights and Measures redefined the meter in terms of a red cadmium spectral line (1m = 1,553,164.13 wavelengths). This definition has since been changed (see krypton).
Occurrence
Cadmium-containing ores are rare and when found they occur in small quantities. Greenockite (CdS), the only cadmium mineral of importance, is nearly always associated with sphalerite (ZnS). Consequently, cadmium is produced mainly as a byproduct from mining, smelting, and refining sulfide ores of zinc, and to a lesser degree, lead and copper. Small amounts of cadmium, about 10% of consumption, are produced from secondary sources, mainly from dust generated by recycling iron and steel scrap. Production in the United States began in 1907 but it was not until after World War I that cadmium came into wide use.
Isotopes
Naturally occurring cadmium is composed of 5 stable isotopes. 28 radioisotopes have been characterized with the most stable being Cd-116 with a half-life of 1.2 X 1021 years, Cd-113 with a half-life of 7.7 quadrillion years, Cd-109 with a half-life of 462.6 days, and Cd-115 with a half-life of 53.46 hours. All of the remaining radioactive isotopes have half-lifes that are less than 2.5 hours and the majority of these have half lifes that are less than 5 minutes. This element also has 8 meta states with the most stable being Cd-113m (t½ 14.1 years), Cd-115m (t½ 44.6 days) and Cd-117m (t½ 3.36 hours).
The isotopes of cadmium range in atomic weight from 96.935 u (Cd-97) to 129.934 amu (Cd-138). The primary decay mode before the second most abundant stable-isotope, Cd-112, is electron capture and the primary mode after is beta emission. The primary decay product before Cd-112 is element 47 (silver) and the primary product after is element 49 (indium).
Precautions
Cadmium is one of the few elements that has no constructive purpose in the human body. This element and solutions of its compounds are extremely toxic even in low concentrations, and will bioaccumulate in organisms and ecosystems. One possible reason for its toxicity is that it interferes with the action of zinc-containing enzymes. Zinc is an important element in biological systems, but cadmium, although similar to zinc chemically in many ways, apparently does not substitute or "stand in" for it at all well. Cadmium may also interfere with biological processes containing magnesium and calcium in a similar fashion.
Inhaling cadmium laden dust quickly leads to respiratory tract and kidney problems which can be fatal (often from renal failure). Ingestion of any significant amount of cadmium causes immediate poisoning and damage to the liver and the kidneys. Compounds containing cadmium are also carcinogenic. Cadmium poisoning is the cause of the itai-itai disease, which literally means "pain pain" in Japanese. In addition to kidney damage, patients suffered from osteoporosis and osteomalacia.
While working with cadmium it is important to do so under a fume hood to protect against dangerous fumes. Silver solder, for example, which contains cadmium, should be handled with care. Serious toxicity problems have resulted from long-term exposure to cadmium plating baths.
See also: Cadmium Poisoning
References
External links
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