Cobalt (Co)
Stable Isotopes of Cobalt
| Isotope | Z(p) | N(n) | Atomic Mass | Natural Abundance | Nuclear Spin |
| Co-59 | 27 | 32 | 58.93320 | 100.00% | 7/2- |
Cobalt was discovered in 1735 by Georg Brandt. Its name derives from the German word kobald, meaning "goblin" or "evil spirit." Minerals containing cobalt were used by the early civilizations of Egypt and Mesopotamia for coloring glass deep blue. Cobalt oxide is used today to add a pink or blue color to glass. It is also an important trace element in soils and necessary for animal nutrition. The most important modern use of cobalt is in the manufacture of various wear-resistant and superalloys. Its alloys have shown high resistance to corrosion and oxidation at high temperatures. Radioactive Cobalt-60 is used in radiography and in the sterilization of food.
A silvery-white, shining, hard, ductile, somewhat malleable metal, cobalt is also ferromagnetic, with permeability two-thirds that of iron. It has exceptional magnetic properties in alloys. It is attached by dilute hydrochloric and sulfuric acids. It corrodes readily in air, and it has unusual coordinating properties, especially the trivalent ion. It is noncombustible except in powder form.
Cobalt occurs in two allotropic modifications over a wide range of temperatures: the crystalline close-packed-hexagonal form is known as the alpha form, which turns into the beta (or gamma) form above 417 ºC.
In finely powdered form, cobalt ignites spontaneously in air. Reactions with acetylene and bromine pentafluoride proceed to incandescence and can become violent. The metal is moderately toxic by ingestion. Inhalation of dusts can damage lungs. Skin contact with powdered material can cause dermatitis.
Properties of Cobalt
| Name | Cobalt |
| Symbol | Co |
| Atomic number | 27 |
| Atomic weight | 58.933 |
| Standard state | Solid at 298 °K |
| CAS Registry ID | 7440-48-4 |
| Group in periodic table | 9 |
| Group name | None |
| Period in periodic table | 4 |
| Block in periodic table | d-block |
| Color | Lustrous, metallic, grayish tinge |
| Classification | Metallic |
| Melting point | 1495 °C |
| Boiling point | 2870 °C |
| Thermal conductivity | 100 W/(m·K) at 298.2 °K |
| Electrical resistivity | 5.6 µΩ·cm at 20 °C |
| Electronegativity | 1.8 |
| Specific heat | 421 J/kg K |
| Heat of vaporization | 375 kJ·mol-1 |
| Heat of fusion | 16.2 kJ·mol-1 |
| Density of solid | 8.86 g/cm3 |
| Electron configuration | [Ar]3d74s2 |
| Oxidation states | 0, +1, +2, +3, +4, +5 |
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