| Calcium - Ca
CAS: 7440-70-2 Description: Silvery, soft metal; tarnishes to grayish white on exposure to air Classification: Alkaline Earth Date of Discovery: 1808 Discoverer: Sir Humphrey Davy Name Origin: Latin calx, "lime" |
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Atomic Number: 20
Number of Neutrons: 20 Atomic Mass: 40.078(4) amu Melting Point: 842 ± 2 °C Boiling Point: 1484 °C Density (293 K): 1.55 g/cm3 Atomic volume: 29.9 cm3/mol Electrical resistivity: 0.298 10-6/cm 
Thermal conductivity: 2.00 W/cmK Enthalpy of atomization: 184 kJ/mol (est.) Enthalpy of vaporization: 153.60 kJ/mol Enthalpy of fusion: 8.540 kJ/mol Specific heat capacity: 0.63 J/gK |
Energy levels: 2-8-8-2
Electron configuration: [Ar]4s2 Crystal Structure: Cubic face centered Atomic radius: 2.23 Å Covalent radius: 1.74 Å Oxidation States: +2 Electronegativity, Pauling: 1.00 Electron affinity: 0.02455 eV First ionization energy: 6.113 eV 2nd ionization energy: 11.871 eV 3rd ionization energy: 50.908 eV Polarizability: 22.8 10-24cm3 |
| Isotope | Natural Abundance | Atomic Mass | Half-life | Decay Mode | Spin |
| 35Ca | 35.0048 | 0.05 s |  + |
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| 36Ca | 35.99309 | 0.1 s | +; +, n |
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| 37Ca | 36.98587 | 0.173 s | +; +, n |
3/2+ | |
| 38Ca | 37.976319 | 0.44 s | + |
0+ | |
| 39Ca | 38.970718 | 0.861 s | - |
3/2+ | |
| 40Ca | 96.941(18) | 39.965912 | Stable | 0+ | |
| 41Ca | 40.9622783 | 1.02 x 105 y | EC | 7/2- | |
| 42Ca | 0.647(9) | 41.9586183 | Stable | 0+ | |
| 43Ca | 0.135(6) | 42.9587668 | Stable | 7/2- | |
| 44Ca | 2.086(12) | 43.955481 | Stable | 0+ | |
| 45Ca | 44.956186 | 162.7 d | - |
7/2- | |
| 46Ca | 0.004(3) | 45.953693 | Stable | 0+ | |
| 47Ca | 46.954546 | 4.536 d | - |
7/2- | |
| 48Ca | 0.187(4) | 47.952533 | Stable | 0+ | |
| 49Ca | 48.955673 | 8.72 m | - |
3/2- | |
| 50Ca | 49.95752 | 14 s | - |
0+ | |
| 51Ca | 50.9615 | 10 s | - |
(3/2-) | |
| 52Ca | 51.9651 | 4.6 s | - |
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| 53Ca | 52.9700 | 0.09 s | - |
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Though lime was prepared by the Romans in the first century under
the name calx, the metal was not discovered until 1808. After learning that Berzelius
and Pontin prepared calcium amalgam by electrolyzing lime in mercury, Davy was
able to isolate the impure metal. Calcium is a metallic element, fifth in abundance in
the earth's crust, of which if forms more than 3%. It is an essential constituent of
leaves, bones, teeth, and shells. Never found in nature uncombined, it occurs
abundantly as limestone (CaCO3), gypsum (CaSO4 · 2H2O), and fluorite (CaF2); apatite is the fluorophosphate or
chlorophosphate of calcium. The metal has a silvery color, is rather hard, and is
prepared by electrolysis of the fused chloride to which calcium fluoride is added to
lower the melting point. Chemically it is one of the alkaline earth elements; it
readily forms a white coating of nitride in air, reacts with water, burns with a
yellow-red flame, forming largely the nitride. The metal is used as a reducing agent
in preparing other metals such as thorium, uranium, zirconium, etc., and is used as a
deoxidizer, desulfurizer, or decarburizer for various ferrous and nonferrous alloys.
It is also used as an alloying agent for aluminum, beryllium, copper, lead, and
magnesium alloys, and serves as a "getter" for residual gases in vacuum tubes, etc.
Its natural and prepared compounds are widely used. Quicklime (CaO), made by
heating limestone and changed into slaked lime by the careful addition of water, is
the great cheap base of chemical refinery with countless uses. Mixed with sand it
hardens as mortar and plaster by taking up carbon dioxide from the air. Calcium
from limestone is an important element in Portland cement. The solubility of the
carbonate in water containing carbon dioxide causes the formation of caves with
stalactites and stalagmites and is responsible for hardness in water. Other important
compounds are the carbide (CaC2), chloride (CaCl2), cyanamide (CaCN2), hypochlorite (Ca(OCl)2), nitrate (Ca(NO3)2), and sulfide (CaS). Natural calcium contains six isotopes. Thirteen other radioactive isotopes are known.
LINKS: Calcium and Osteoporosis: How Much is Enough? Calcium Information Compton's Online: Calcium Interesting Kidney Stone Photographs UIUC: Calcium Return
Sources for the information on this website include: Lide, David R., ed. CRC Handbook of Chemistry and Physics, 78th Ed., 1997-1998. |
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