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Sunday, February 21, 2010

Calcium Facts

Calcium isn't found free in nature, but it can be purified into a soft silvery-white metal. Calcium is the 5th most abundant element in the Earth's crust, present at a level of about 3% in the oceans and soil. The element is essential for animal and plant nutrition. Calcium participates in many biochemical reactions, including building skeletal systems and moderating muscle action.

Calcium is a metal. It readily oxidizes in air.
Because it makes up such a large part of the skeleton,
about one-third of the mass of human body 
comes from calcium, after water has been removed.


Atomic Number: 20
Symbol: Ca
Atomic Weight: 40.078
Discovery: Sir Humphrey Davy Davy 1808 (England)
Electron Configuration: [Ar] 4s2
Word Origin: Latin calx, calcis: lime

Properties: The melting point of calcium is 839 +/- 2°C, boiling point is 1484°C, specific gravity is 1.55 (20°C), with a valence of 2. Calcium is a silvery white, soft alkaline earth metal. Although none of the alkaline earths occur free in nature, calcium compounds are abundant.

Uses: Calcium is essential for human nutrition. Animals skeletons get their rigidity primarily from calcium phosphate. The eggs of birds and shells of mollusks are comprised of calcium carbonate. Calcium is also necessary for plant growth. Calcium is used as a reducing agent when preparing metals from their halogen and oxygen compounds; as a reagent in purification of inert gases; to fix atmospheric nitrogen; as a scavenger and decarbonizer in metallurgy; and for making alloys. Calcium compounds are used in making lime, bricks, cement, glass, paint, paper, sugar, glazes, as well as for many other uses.

Sources: The Romans prepared lime (called calx) in the first century, but the metal was not discovered until 1808. Berzelius and Pontin prepared calcium amalgam by electrolyzing lime in mercury. Davy isolated the impure metal. The metal may be prepared by electrolysis of CaCl2 at a temperature slightly above its melting point. Calcium is the fifth most abundant element in the earth's crust, making up 3.22% of the earth, air, and oceans. Natural forms of calcium include limestone (CaCO3), gypsum (CaSO4·2H2O), and fluorite (CaF2). Apatite is the fluorophosphate or chlorophosphate of calcium.

Element Classification: alkaline-earth metal
Density (g/cc): 1.55
Melting Point (K): 1112
Boiling Point (K): 1757
Appearance: fairly hard, silvery-white metal
Atomic Radius (pm): 197
Atomic Volume (cc/mol): 29.9
Covalent Radius (pm): 174
Ionic Radius: 99 (+2e)
Specific Heat (@20°C J/g mol): 0.653
Fusion Heat (kJ/mol): 9.20
Evaporation Heat (kJ/mol): 153.6
Debye Temperature (K): 230.00
Pauling Negativity Number: 1.00
First Ionizing Energy (kJ/mol): 589.4
Oxidation States: 2
Lattice Structure: Face-Centered Cubic
Lattice Constant (Å): 5.580

References: Los Alamos National Laboratory (2001), Crescent Chemical Company (2001), Lange's Handbook of Chemistry (1952), CRC Handbook of Chemistry & Physics (18th Ed.)

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