Cadmium

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48 silvercadmiumindium
Zn

Cd

Hg
File:Cd-TableImage.png
General
Name, Symbol, Number cadmium, Cd, 48
Chemical series transition metals
Group, Period, Block 12, 5, d
Appearance silvery gray metallic
Cd,48.jpg
Standard atomic weight 112.411(8)  g·mol−1
Electron configuration [Kr] 4d10 5s2
Electrons per shell 2, 8, 18, 18, 2
Physical properties
Phase solid
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
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 (scale Pauling)
Ionization energies 1st: 867.8 kJ/mol
2nd: 1631.4 kJ/mol
3rd: 3616 kJ/mol
Atomic radius 155pm
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−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
Poisson ratio 0.30
Mohs hardness 2.0
Brinell hardness 203  MPa
CAS registry number 7440-43-9
Selected isotopes
iso NA half-life DM DE (MeV) DP
106Cd 1.25% >9.5×1017 y εε2ν - 106Pd
107Cd syn 6.5 h ε 1.417 107Ag
108Cd 0.89% >6.7×1017 y εε2ν - 108Pd
109Cd syn 462.6 d ε 0.214 109Ag
110Cd 12.49% Cd is stable with 62 neutrons
111Cd 12.8% Cd is stable with 63 neutrons
112Cd 24.13% Cd is stable with 64 neutrons
113Cd 12.22% 7.7×1015 y β- 0.316 113In
113mCd syn 14.1 y β- 0.580 113In
IT 0.264 113Cd
114Cd 28.73% >9.3×1017 y ββ2ν - 114Sn
115Cd syn 53.46 h β- 1.446 115In
116Cd 7.49% 2.9×1019 y ββ2ν - 116Sn
References

Editor-In-Chief: C. Michael Gibson, M.S., M.D. [3]


Overview

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.

Notable characteristics

Cadmium is a soft, malleable, ductile, toxic, bluish-white bivalent metal. It is similar in many respects to zinc but reacts to form more complex compounds.

The most common oxidation state of cadmium is +2, though rare examples of +1 can be found.

Applications

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.

History

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".

Toxicity

Main article: Cadmium poisoning
Cadmium metal

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.[1]

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.[2] 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.[3] Cadmium is one of six substances banned by the European Union's Restriction on Hazardous Substances (RoHS) directive, which bans carcinogens in computers.

Cadmium and several cadmium-containing compounds are known carcinogens and can induce many types of cancer.[4]

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.

Precautions

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.[5] Solder, for example, which may contain cadmium, should be handled with care.

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References

  1. [1] Principles and Methods of Toxicology (fourth edition). A. Wallace Hayes. Taylor and Francis Publishing Inc.; Philadelphia, 2001.
  2. EPA summary on cadmium
  3. [2] Environmental cadmium exposure, adverse effects, and preventative measures in Japan. Nogowa et al. Biometals. 2004 Oct; 17(5):581-7.
  4. 11th Report on Carcinogens provided by the National Toxicology Program
  5. OSHA Solutions for workplace cadmium exposure

External links


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