Calcium

iso	NA	half-life	DM	DE M eV	DP
⁴⁰Ca	96.941%	Ca is stable with 20 neutrons
⁴¹Ca	{syn.}	103,000y	epsilon	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%	>6×10¹⁸y	beta^-	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.

Table of contents

1 Notable Characteristics
2 Applications
3 History
4 Occurrence
5 Compounds
6 Isotopes
7 External Links

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.

Applications

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 Ca (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^-* --> �Cl₂ (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.