Cadmium

silver – cadmium – indium Zn Cd Hg       Full table
General
Name, Symbol, Number	Cadmium, Cd, 48
Chemical series	Transition metals
Group, Period, Block	12, 5, d
Density, Hardness	8650 kg/m3, 2
Appearance	Silvery gray metallic Missing image Cd,48.jpg
Atomic properties
Atomic weight	112.411 amu
Atomic radius (calc.)	155 (161) pm
Covalent radius	148 pm
van der Waals radius	158 pm
Electron configuration	[Kr]4d10 5s2
e- 's per energy level	2, 8, 18, 18, 2
Oxidation states (Oxide)	2 (mildly basic)
Crystal structure	Hexagonal
Physical properties
State of matter	Solid
Melting point	594.22 K (321.07 ?C)
Boiling point	1040 K (767.22 ?C)
Molar volume	13.00 ×10-6 m3/mol
Heat of vaporization	100 kJ/mol
Heat of fusion	6.192 kJ/mol
Vapor pressure	14.8 Pa at 597 K
Speed of sound	2310 m/s at 293.15 K
Miscellaneous
Electronegativity	1.69 (Pauling scale)
Specific heat capacity	233 J/(kg*K)
Electrical conductivity	13.8 106/(m·ohm)
Thermal conductivity	96.8 W/(m*K)
1st ionization potential	867.8 kJ/mol
2nd ionization potential	1631.4 kJ/mol
3rd ionization potential	3616 kJ/mol
Most stable isotopes
iso NA half-life DM DE MeV DP 108Cd 0.89% Cd is stable with 60 neutrons 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 E15 y β- 0.316 113In 113Cdm {syn.} 14.1 y β- IT 0.580 0.264 113In   114Cd 28.73% Cd is stable with 66 neutrons 116Cd 7.49% Cd is stable with 68 neutrons
SI units & STP are used except where noted.

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.

Contents

1 Notable characteristics 2 Applications 3 History 4 Occurrence 5 Isotopes 6 Precautions 7 References

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;

• Used in some of the lowest melting alloys.
• Due to a low coefficient of friction and very good fatigue resistance, it is used in bearing alloys.
• 6% of cadmium finds use in electroplating.
• Many kinds of solder contain this metal.
• As a barrier to control nuclear fission.
• Compounds containing cadmium are used in black and white television phosphors and also in the blue and green phosphors for color television picture tubes.
• Cadmium forms various salts, with cadmium sulfide being the most common. This sulfide is used as a yellow pigment.
• Used in some semiconductors such as cadmium sulfide, cadmium selenide, and cadmium telluride, which can be used for light detection or solar cells. HgCdTe is sensitive to infrared.
• Some cadmium compounds are employed in PVC as stabilizers.
• Used in the first neutrino detector.

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 6 stable isotopes. 27 radioisotopes have been characterized with the most stable being 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 (t_? 14.1 years), Cd-115m (t_? 44.6 days) and Cd-117m (t_? 3.36 hours).

The isotopes of cadmium range in atomic weight from 96.935 amu (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

• Los Alamos National Laboratory – Cadmium (http://periodic.lanl.gov/elements/48.html)

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