PTL:Cobalt
From ChemEd Collaborative
Cobalt is a transition metal in Group VIIIB (Group 9) and the 4th period. Other members of the cobalt group are rhodium (Rh) and iridium (Ir).
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Discovered
Georg Brandt first described metallic cobalt in 1735. He discovered Cobalt while attempting to prove that some minerals were able to turn glass blue due to a previously undiscovered element. This was contrary to the popular belief of the time that bismuth was responsible for this phenomenon.
Name
The name is derived from the German word, Kobold, for "goblin" or "evil spirit", since the presence of cobalt in ores of other metals made smelting difficult. The symbol Co is an abbreviation of the name.
Characteristics
Cobalt is a brittle, hard metal. In bulk form it is silvery white, lustrous, closely resembling iron and nickel in appearance. It is not combustible in its solid form. In the solid state, the metal has a hexagonal closest packed structure.
Found
Cobalt occurs in the minerals cobaltite (CoAsS), smaltite (Co0.75Ni0.25As2.5), and erythrite [Co3(AsO4)2·8(H2O)], and is often associated with nickel, silver, lead, copper, and iron ores, from which it is most frequently obtained as a by-product. It is also present in meteorites.
Reactions
It reacts with oxygen to give cobalt(III) and cobalt(II) oxide. With acids it gives highly colored Co(II) and Co(III) salts.
Uses
Cobalt metal has a magnetic permeability about two-thirds that of iron. It is alloyed with iron, nickel, and other metals to make Alnico, an alloy of unusual magnetic strength with many important uses. Stellite alloys, containing cobalt, chromium, and tungsten, are used for high-speed, heavy-duty, high-temperature cutting tools, and for dies. Cobalt is also used in other magnet steels and stainless steels, and in alloys used in jet turbines and turbo-superchargers. The metal is used in electroplating because of its appearance, hardness, and resistance to oxidation.
The salts have been used for centuries for the production of brilliant and permanent [blue colors in porcelain, glass, pottery, tiles and enamels].
Cobalt chloride can be used as an invisible ink. It is almost colorless in dilute solution when applied to paper; upon heating it undergoes dehydration and turns blue, becoming colorless again when the heat is removed and water is taken up by the molecule. Many compounds of cobalt are highly colored.
Cobalt carefully used in the form of the chloride, sulfate, acetate, or nitrate has been found effective in correcting a certain mineral deficiency disease in animals. [Vitamin B-12] is a complex of [cobalt with an organic molecule]. Soils should contain 0.13 to 0.30 parts per million. of cobalt for proper animal nutrition.
Cobalt--60, an artificial isotope, is an important gamma ray source, and is extensively used as a radiotherapeutic agent. Single compact sources of Cobalt--60 are readily available and have a gamma ray output equivalent to thousands of grams of radium.
Physical Properties
Atomic Mass= 58.9332
Optical Reflectivity= 67%
Specific Heat= .42 J/gK
Coefficient of Lineal Thermal Expansion= 13.36x10^-6
Vapor Pressure= 175 Pa
Cobalt is estimated to have an oceanic abundance of 2x10^-5 mg/L
Atomic Properties
As an atom Cobalt has 32 neutrons, 27 protons and 27 electrons. Furthermore it has 9 valence electons as an atom: 7 in the 3d shell and 2 in the 4s shell.
Covalent Radius= 1.16Å
Ionic Radius= .745Å
Valence electron potential= 38.7
Molar Volume= 6.61 cm^3/mole
Emission Spectra
This is the emission spectra for Cobalt.
