Calcium
| Calcium
| |
|---|---|
| Symbol | Ca |
| Atomic number | 20 |
| Atomic mass | 40.08 amu |
Calcium is a silver-white light metal discovered in 1808.
Distinguishing properties
Calcium makes up of about 3.4% of the earth's crust. This makes it the 5th most abundant in the earth's crust and the third most abundant metal. It oxidizes in moist air and the surface becomes coated with calcium oxide, hyrdroxide and carbonate.
Occurrence
Calcium metal is prepared by electrolysis of molten calcium chloride. Calcium is used primarily in the form of lime in steelmaking. Slaked lime is an important material to control air pollution. Lime is also important as a raw material in chemical manufacture, water treatment, papermaking and as concrete in the construction industry.
Calcium carbonate also occurs in other natural forms such as marine animal shells and pearls. Calcium carbonate is the chalk that makes up the White Cliffs of Dover. The chalk is the remains of the shells of marine microorganisms that died and sank to the bottom of the ancient seas.
Boiler scale is an extremely hard incrustation of calcium and magnesium compounds. They are usually insoluble carbonates and sulfates. The scale forms on the inner surfaces of boilers where "hard" water has been in contact with them for long periods of time.
Calcium is also presence in our bodies. In an adult, there is about 1 kg calcium in the teeth and bones. Calcium also plays a role in regulating heartbeat.
Usage
Plaster of Paris is calcium sulphate hemihydrate ((CaSO4)2.H2O). The largest use of plaster of Paris is in the building industry as wall plasters and wall boards. It is used for architectural decorations and in the medical field for the setting of broken bones. In addition it is used as moulds in the production of ceramics and of metallic jewellry.
Common compounds
Large amounts of calcium are found in:
- the mineral, dolomite, MgCO3.CaCO3,
- minerals of calcium carbonate, CaCO3, like limestone, deposits of marl, chalk, marble, calcite, and aragonite. Calcite is one of the most common and widely distributed minerals in the world. It occurs in many different shades of colour. This typical example consists of many colourless crystals. Other calcite crystals vary in pale tints to golden-yellow in colour.
- the mineral, gypsum, CaSO4.2H2O,
- the mineral, fluorite, CaF2. Fluorite occurs in many different colours. It may be yellow, green, blue, pink, purple or black. It occurs in veins with lead and silver ores. Fluorite is used to make hydrofluoric acid that is used in making pottery, glass, plastics, and in processing bauxite.
