potassium – calcium – scandium Mg Ca Sr       Full table
General
Name, Symbol, Number	calcium, Ca, 20
Series	alkaline earth metal
Group, Period, Block	2 (IIA), 4, s
Density, Hardness	1550 kg/m3, 1.75
Appearance	silvery white
Atomic properties
Atomic weight	40.078 amu
Atomic radius (calc.)	180 (194) pm
Covalent radius	174 pm
van der Waals radius	no information
Electron configuration	[Ar]4s2
e- 's per energy level	2, 8, 8, 2
Oxidation states (Oxide)	2 (strong base)
Crystal structure	Cubic face centered
Physical properties
State of matter	solid (paramagnetic)
Melting point	1115 K (1548°F)
Boiling point	1757 K (2703°F)
Molar volume	26.20 ×10-6 m3/mol
Heat of vaporization	153.6 kJ/mol
Heat of fusion	8.54 kJ/mol
Vapor pressure	254 Pa at 1112 K
Speed of sound	3810 m/s at 293.15 K
Miscellaneous
Electronegativity	1.00 (Pauling scale)
Specific heat capacity	632 J/(kg*K)
Electrical conductivity	29.8 106/m ohm
Thermal conductivity	201 W/(m*K)
1st ionization potential	589.8 kJ/mol
2nd ionization potential	1145.4 kJ/mol
3rd ionization potential	4912.4 kJ/mol
Most stable isotopes
iso NA half-life DM DE MeV DP 40Ca 96.941% Ca is stable with 20 neutrons 41Ca {syn.} 103,000 y µ 0.421 41K 42Ca 0.647% Ca is stable with 22 neutrons 43Ca 0.135% Ca is stable with 23 neutrons 44Ca 2.086% Ca is stable with 24 neutrons 46Ca 0.004% Ca is stable with 26 neutrons 48Ca 0.187% >6×1018 y   4.272 48Ti
SI units & STP are used except where noted.

Calcium is a chemical element in the periodic table that has the symbol Ca and atomic number 20. Calcium is a soft grey alkaline earth metal that is used as a reducing agent in the extraction of thorium, zirconium and uranium. This element is also the fifth most abundant element in the earth's crust. It is essential for living organisms, particularly in cell physiology.

Notable characteristics

Calcium is a rather hard element that is purified by electrolysis from calcium fluoride that burns with a yellow-red flame and forms a white nitride coating when exposed to air. It reacts with water displacing hydrogen and forming calcium hydroxide.

Calcium is an important component of a healthy diet. Its minor deficit can affect bone and teeth formation. Its excess can lead to kidney stones. Vitamin D is needed to absorb calcium. Dairy products are an excellent source of calcium.

For more information about Ca in living nature, see calcium in biology.

Other uses include:

• Reducing agent in the extraction of other metals such as uranium, zirconium, and thorium.
• Deoxidizer, desulfurizer, or decarburizer for various ferrous and nonferrous alloys.
• Alloying agent used in the production of aluminum, beryllium, copper, lead, and magnesium alloys.

History

(Latin calx, lime) Lime was prepared and used by the Romans as early as the 1st century, but calcium was not discovered until 1808. After learning that Berzelius and Pontin prepared calcium amalgam by electrolyzing lime in mercury, Sir Humphry Davy was able to isolate the impure metal.

Occurrence

Calcium is the fifth most abundant element in the earth's crust (forming more than 3%) and is an essential part of leaves, bones, teeth, and shells. Due to its chemical reactivity with air and water, calcium is never found in nature unbound to other elements, except in living organisms where Ca²⁺ plays a key role in cell physiology. This metallic element is found in quantity in limestone, gypsum, and fluorite. Apatite is the fluorophosphate or chlorophosphate of calcium. Electrolysis of molten calcium chloride (CaCl₂) can be used to isolate pure calcium.
Isolation (* follow):
cathode: Ca²⁺* + 2e^- --> Ca
anode: Cl^-* --> ½Cl₂ (gas) + e^-

Compounds

Quicklime (CaO) is used in many chemical refinery processes and is made by heating and carefully adding water to limestone. When CaO is mixed with sand it hardens into a mortar and is turned into plaster by carbon dioxide uptake. Mixed with other compounds, CaO forms an important part of Portland cement.

When water percolates through limestone or other soluble carbonate rocks, it partially disolves part of the rock and causes cave formation and characteristic stalactites and stalagmites and also forms hard water. Other important calcium compounds are nitrate, sulfide, chloride, carbide, cyanamide, and hypochlorite.

Isotopes

Calcium has six stable isotopes, two of which occur in nature: stable Ca-40 and radioactive Ca-41 with a half-life = 103,000 years. 97% of the element is in the form of Ca-40. Ca-40 is one of the daughter products of K-40 decay, along with Ar-40. While K-Ar dating has been used extensively in the geological sciences, the prevalence of Ca-40 in nature has impeded its use in dating. Techniques using mass spectrometry and a double spike isotope dilution have been used for K-Ca age dating. Unlike cosmogenic isotopes that are produced in the atmosphere, Ca-41 is produced by neutron activation of Ca-40. Most of its production is in the upper meter or so of the soil column where the cosmogenic neutron flux is still sufficiently strong. Ca-41 has received much attention in stellar studies because Ca-41 decays to K-41, a critical indicator of solar-system anomalies.

External links

• WebElements.com – Calcium (http://www.webelements.com/webelements/elements/text/Ca/index.html)
• EnvironmentalChemistry.com – Calcium (http://environmentalchemistry.com/yogi/periodic/Ca.html)