|Name, Symbol, Number||cadmium, Cd, 48|
|Chemical series||transition metals|
|Group, Period, Block||12, 5, d|
|Appearance||silvery gray metallic |
|Standard atomic weight||112.411(8) g·mol−1|
|Electron configuration||[Kr] 4d10 5s2|
|Electrons per shell||2, 8, 18, 18, 2|
|Density (near r.t.)||8.65 g·cm−3|
|Liquid density at m.p.||7.996 g·cm−3|
|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−1|
|Heat of vaporization||99.87 kJ·mol−1|
|Heat capacity||(25 °C) 26.020 J·mol−1·K−1|
(mildly basic oxide)
|Electronegativity||1.69 (scale Pauling)|
|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|
|Magnetic ordering||no data|
|Electrical resistivity||(22 °C) 72.7 nΩ·m|
|Thermal conductivity||(300 K) 96.6 W·m−1·K−1|
|Thermal expansion||(25 °C) 30.8 µm·m−1·K−1|
|Speed of sound (thin rod)||(20 °C) 2310 m/s|
|Young's modulus||50 GPa|
|Shear modulus||19 GPa|
|Bulk modulus||42 GPa|
|Brinell hardness||203 MPa|
|CAS registry number||7440-43-9|
Cadmium (pronounced /ˈkædmiəm/) is a chemical element with the symbol Cd and atomic number 48. A relatively rare, soft, bluish-white, transition metal, cadmium is known to cause cancer and occurs with zinc ores. Cadmium is used largely in batteries and pigments, for example in plastic products.
The most common oxidation state of cadmium is +2, though rare examples of +1 can be found.
Uses of cadmium include:
- Cadmium forms various salts, with cadmium sulfide being the most common. This sulfide is used as a yellow pigment. Cadmium selenide can be used as red pigment, commonly called cadmium red. To painters who work with the pigment, cadmium yellows, oranges and reds are the most potent colours to use. In fact, during production these colours are significantly toned down before they are ground with oils and binders, or blended into watercolours, gouaches, acrylics, and other paint and pigment formulations. These pigments are toxic and it is recommended to use a barrier cream on your hands to prevent absorption through the skin when working with them. There is no such thing as cadmium blue, green or violet.
- Used to block voltage-dependent calcium channels from fluxing calcium ions in molecular biology.
Cadmium (Latin cadmia, Greek καδμεία meaning "calamine", a Cadmium-bearing mixture of minerals, which was named after the Greek mythological character, Κάδμος (Cadmus)) 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".
Cadmium is an occupational hazard associated with industrial processes such as metal plating and the production of nickel-cadmium batteries, pigments, plastics and other synthetics. The primary route of exposure in industrial settings is inhalation. Inhalation of cadmium-containing fumes can result initially in metal fume fever but may progress to chemical pneumonitis, pulmonary edema, and death.
Cadmium is also a potential environmental hazard. Human exposures to environmental cadmium are primarily the result of the burning of fossil fuels and municipal wastes. However, there have been notable instances of toxicity as the result of long-term exposure to cadmium in contaminated food and water. In the decades following World War II, Japanese mining operations contaminated the Jinzu River with cadmium and traces of other toxic metals. Consequently, cadmium accumulated in the rice crops growing along the riverbanks downstream of the mines. The local agricultural communities consuming the contaminated rice developed Itai-itai disease and renal abnormalities, including proteinuria and glucosuria. Cadmium is one of six substances banned by the European Union's Restriction on Hazardous Substances (RoHS) directive, which bans carcinogens in computers.
Current research has found that cadmium toxicity may be carried into the body by zinc binding proteins; in particular, proteins that contain zinc finger protein structures. Zinc and cadmium are in the same group on the periodic table, contain the same common oxidation state (+2), and when ionized are almost the same size. Due to these similarities, cadmium can replace zinc in many biological systems, in particular, systems that contain softer ligands such as sulfur. Cadmium can bind up to ten times more strongly than zinc in certain biological systems, and is notoriously difficult to remove. In addition, cadmium can replace magnesium and calcium in certain biological systems, although these replacements are rare.
Tobacco smoking is the most important single source of cadmium exposure in the general population. It has been estimated that about 10% of the cadmium content of a cigarette is inhaled through smoking. The absorption of cadmium from the lungs is much more effective than that from the gut, and as much as 50% of the cadmium inhaled via cigarette smoke may be absorbed.
On average, smokers have 4-5 times higher blood cadmium concentrations and 2-3 times higher kidney cadmium concentrations than non-smokers. Despite the high cadmium content in cigarette smoke, there seems to be little exposure to cadmium from passive smoking. No significant effect on blood cadmium concentrations could be detected in children exposed to environmental tobacco smoke.
While working with cadmium it is important to do so under a fume hood or with the use of an appropriate respirator to protect against dangerous fumes. Solder, for example, which may contain cadmium, should be handled with care.
|Wikimedia Commons has media related to Cadmium.|
-  Principles and Methods of Toxicology (fourth edition). A. Wallace Hayes. Taylor and Francis Publishing Inc.; Philadelphia, 2001.
- EPA summary on cadmium
-  Environmental cadmium exposure, adverse effects, and preventative measures in Japan. Nogowa et al. Biometals. 2004 Oct; 17(5):581-7.
- 11th Report on Carcinogens provided by the National Toxicology Program
- OSHA Solutions for workplace cadmium exposure
- IARC Monograph "Cadmium and Cadmium Compounds"
- National Pollutant Inventory - Cadmium and compounds
- WebElements.com – Cadmium
- Los Alamos National Laboratory – Cadmium
-  Warning Moose and Deer Liver
- National Institute for Occupational Safety and Health - Cadmium Page
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