Calcium

For other uses, see Calcium (disambiguation).

20 potassium ← calcium → scandium Mg ↑ Ca ↓ Sr periodic table
General
Name, Symbol, Number	calcium, Ca, 20
Chemical series	alkaline earth metals
Group, Period, Block	2, 4, s
Appearance	silvery white
Atomic mass	40.078(4) g/mol
Electron configuration	[Ar] 4s2
Electrons per shell	2, 8, 8, 2
Physical properties
Phase	solid
Density (near r.t.)	1.55 g/cm³
Liquid density at m.p.	1.378 g/cm³
Melting point	1115 K (842 °C, 1548 °F)
Boiling point	1757 K (1484 °C, 2703 °F)
Heat of fusion	8.54 kJ/mol
Heat of vaporization	154.7 kJ/mol
Heat capacity	(25 °C) 25.929 J/(mol·K)
Vapor pressure P/Pa 1 10 100 1 k 10 k 100 k at T/K 864 956 1071 1227 1443 1755
Atomic properties
Crystal structure	cubic face centered
Oxidation states	2 (strongly basic oxide)
Electronegativity	1.00 (Pauling scale)
Ionization energies (more)	1st: 589.8 kJ/mol
	2nd: 1145.4 kJ/mol
	3rd: 4912.4 kJ/mol
Atomic radius	180 pm
Atomic radius (calc.)	194 pm
Covalent radius	174 pm
Miscellaneous
Magnetic ordering	paramagnetic
Electrical resistivity	(20 °C) 33.6 nΩ·m
Thermal conductivity	(300 K) 201 W/(m·K)
Thermal expansion	(25 °C) 22.3 µm/(m·K)
Speed of sound (thin rod)	(20 °C) 3810 m/s
Speed of sound (thin rod)	(r.t.) 20 m/s
Shear modulus	7.4 GPa
Bulk modulus	17 GPa
Poisson ratio	0.31
Mohs hardness	1.75
Brinell hardness	167 MPa
CAS registry number	7440-70-2
Notable isotopes
Main article: Isotopes of calcium iso NA half-life DM DE (MeV) DP 40Ca 96.941% Ca is stable with 20 neutrons 41Ca syn 1.03×105 y ε - 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 45Ca syn 162.7 d β- 0.258 45Sc 46Ca 0.004% >2.8×1015 y β-β- ? 46Ti 47Ca syn 4.536 d β- 0.694, 1.99 47Sc γ 1.297 - 48Ca 0.187% >4×1019 y β-β- ? 48Ti

Calcium (chemical symbol Ca, atomic number 20) is the fifth most abundant chemical element in the Earth's crust. Soft gray in color, it is classified as an alkaline earth metal. It is used as a reducing agent in the extraction of thorium, zirconium, and uranium. It is essential for living organisms, particularly in cell physiology, and is the most common metal in many animals.

• Calcium is essential in muscle contraction, oocyte activation, building strong bones and teeth, blood clotting, nerve impulse transmission, regulating heartbeat, and fluid balance within cells. In the United States, between about 50% and 75% of adults do not get sufficient calcium in their diet. Adults need between 1,000 and 1,300 milligrams (mg) of calcium in their daily diet.

Notable characteristics

In the periodic table, calcium lies in group 2 (former group 2A), between magnesium and strontium, as a member of the series of alkaline earth metals. In addition, it is in period 4, between potassium and scandium.

It can be extracted by electrolysis from calcium fluoride. It 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, an alkaline substance.

The most abundant isotope, ⁴⁰Ca, has a nucleus of 20 protons and 20 neutrons. Its electron configuration is: 2 electrons in the K shell (principal quantum number 1), 8 in the L shell (principal quantum number 2), 8 in the M shell (principal quantum number 3), and 2 in the N shell (principal quantum number 4). The outer shell is the valence shell, with 2 electrons in the lone 4s orbital, the 3p orbitals being empty.

Occurrence

Calcium is not naturally found in its elemental state. Calcium is found mostly in soil systems as limestone, gypsum and fluorite. Stalagmites and stalactites contain calcium carbonate. Being an essential macromineral in the human diet, soil conservation practices often consider the sustainable equilibrium of calcium concentrations in the earth.

Applications

Calcium is an important component of a healthy diet. A deficit can affect bone and tooth formation, while overretention can cause kidney stones. Vitamin D is needed to absorb calcium. Dairy products, such as milk and cheese, are a well-known source of calcium. However, some individuals are allergic to dairy products and even more people, particularly those of non-European descent, are lactose-intolerant, leaving them unable to consume dairy products. Fortunately, many other good sources of calcium exist. These include: seaweeds such as kelp, wakame and hijiki; nuts and seeds (like almonds and sesame); beans; seafood such as oysters and shrimp; soft-boned fish; amaranth; whole wheat; collard greens; okra; rutabaga; broccoli; and fortified products such as orange juice and bread.

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

Other uses include:

• as a reducing agent in the extraction of other metals, such as uranium, zirconium, and thorium.
• as a deoxidizer, desulfurizer, or decarbonizer for various ferrous and nonferrous alloys.
• as an alloying agent used in the production of aluminium, beryllium, copper, lead, and magnesium alloys.
• in the making of cements and mortars to be used in construction.

History

Calcium (Latin calcis, meaning "lime") was known as early as the first century when the Ancient Romans prepared lime as calcium oxide. It was not actually isolated until 1808 in England when Sir Humphrey Davy electrolyzed a mixture of lime and mercuric oxide. Davy was trying to isolate calcium and when he heard that Berzelius and Pontin prepared calcium amalgam by electrolyzing lime in mercury, he tried it himself. He worked with electrolysis throughout his life and also discovered/isolated magnesium, strontium and barium.

Compounds

Calcium, combined with phosphate to form hydroxylapatite, is the mineral portion of human and animal bones and teeth. The mineral portion of some corals can also be transformed into hydroxylapatite.

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

When water percolates through limestone or other soluble carbonate rocks, it partially dissolves 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 four stable isotopes (⁴⁰Ca and ⁴²Ca through ⁴⁴Ca), plus two more isotopes (⁴⁶Ca and ⁴⁸Ca) that have such long half-lives that for all practical purposes they can be considered stable. It also has a cosmogenic isotope, radioactive ⁴¹Ca, which has a half-life of 103,000 years. Unlike cosmogenic isotopes that are produced in the atmosphere, ⁴¹Ca is produced by neutron activation of ⁴⁰Ca. Most of its production is in the upper metre or so of the soil column where the cosmogenic neutron flux is still sufficiently strong. ⁴¹Ca has received much attention in stellar studies because it decays to ⁴¹K, a critical indicator of solar-system anomalies.

97% of naturally occurring calcium is in the form of ⁴⁰Ca. ⁴⁰Ca is one of the daughter products of ⁴⁰K decay, along with ⁴⁰Ar. While K-Ar dating has been used extensively in the geological sciences, the prevalence of ⁴⁰Ca 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.

Health and nutrition

• Calcium is essential in muscle contraction, oocyte activation, building strong bones and teeth, blood clotting, nerve impulse transmission, regulating heartbeat, and fluid balance within cells. In the United States, between about 50% and 75% of adults do not get sufficient calcium in their diet. Adults need between 1,000 and 1,300 milligrams (mg) of calcium in their daily diet.

Dairy products and calcium

Milk, yogurt, cheese and other dairy products are a prime source of calcium and are also fortified with vitamin D. Calcium is the most abundant mineral in the body, but it is also the one most likely to be inadequately supplied in the diet.

Healthy bones and teeth

Calcium is essential for the normal growth and maintenance of bones and teeth, and calcium requirements must be met throughout life. Requirements are greatest during periods of growth, such as childhood, during pregnancy and when breast-feeding. Long-term calcium deficiency can lead to osteoporosis, in which the bone deteriorates and there is an increased risk of fractures. Calcium needs can be met by eating or drinking at least three or four servings of dairy products daily.

Some dairy products, such as hard cheese and whole milk, do contain a significant amount of saturated fat, which can contribute to cardiovascular disease. Therefore, a diet consisting of low-fat dairy products should be considered. A low-fat variety of cheese made with part-skim milk, such as mozzarella, ricotta, cottage or farmer's cheese might be chosen.

For those with an intolerance or allergy to dairy products, substitutes such as soya or rice milk often have calcium added to them.

Dietary calcium supplements

There are conflicting recommendations about when to take calcium supplements. However, most experts agree that no more than 500 mg should be taken at a time – any excess will go to waste. It is recommended to spread doses throughout the day, with the last dose near bedtime. Recommended daily calcium intake varies from 1000 to 1500 milligrams, depending upon the stage of life.

In July 2006, a report citing research from Fred Hutchinson Cancer Research Center in Seattle, Washington claimed that women in their 50's gained 5 pounds less in a period of 10 years by taking more than 500mg of calcium supplements than those who did not. However, the doctor in charge of the study, Dr. Alejandro J. Gonzalez also noted it would be stretching it to suggest calcium supplements as a weight-limiting aid.

• Calcium carbonate is the most common and least expensive calcium supplement. It can be difficult to digest and causes gas in some people. Taking magnesium with it can help to prevent constipation. Calcium carbonate is 40% elemental calcium. 1000 mg will provide 400 mg of calcium. Take this supplement with food to aid in absorption.

• Calcium citrate is more easily absorbed (bioavailability is 2.5 times higher than calcium carbonate), easier to digest and less likely to cause constipation and gas than calcium carbonate. It also has a lower risk of contributing to the formation of kidney stones. Calcium citrate is 21% elemental calcium. 1000 mg will provide 210 mg of calcium. It is more expensive than calcium carbonate and more of it must be taken to get the same amount of calcium.

• Calcium phosphate costs more than calcium carbonate, but less than calcium citrate. It is easily absorbed and is less likely to cause constipation and gas than either.

• Calcium lactate and calcium aspartate are both more easily digested, but more expensive than calcium carbonate.

See also

• Calcium compounds
• Disorders of calcium metabolism

References

ISBN links support NWE through referral fees

• Rebecca J. Donatelle. Health, The Basics. 6th ed. San Francisco: Pearson Education, Inc. 2005.

External links

• WebElements.com – Calcium
• USDA National Nutrient Database, Calcium content of selected foods

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