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Calcium

2007 Schools Wikipedia Selection. Related subjects: Chemical elements


                20             potassium ← calcium → scandium
                Mg
                ↑
                Ca
                ↓
                Sr

                                  Periodic Table - Extended 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] 4s^2
                                            Electrons per shell 2, 8, 8, 2
                                                       Physical properties
                                                               Phase solid
                                       Density (near r.t.) 1.55 g·cm^−3
                                   Liquid density at m.p. 1.378 g·cm^−3
                                                     Melting point 1115  K
                                                     (842 ° C, 1548 ° F)
                                                      Boiling point 1757 K
                                                    (1484 ° C, 2703 ° F)
                                          Heat of fusion 8.54 kJ·mol^−1
                                   Heat of vaporization 154.7 kJ·mol^−1
                         Heat capacity (25 °C) 25.929 J·mol^−1·K^−1

   CAPTION: 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^−1
                                                  2nd: 1145.4 kJ·mol^−1
                                                  3rd: 4912.4 kJ·mol^−1
                                                      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^−1·K^−1
                       Thermal expansion (25 °C) 22.3 µm·m^−1·K^−1
                               Speed of sound (thin rod) (20 °C) 3810 m/s
                                                    Young's modulus 20 GPa
                                                     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
                                                         Selected isotopes

                 CAPTION: Main article: Isotopes of calcium

                        iso    NA     half-life     DM    DE ( MeV)   DP
                       ^40Ca 96.941% Ca is stable with 20 neutrons
                       ^41Ca syn     1.03×10^5 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%  >2.8×10^15 y β^-β^-  ?          ^46Ti
                       ^47Ca syn     4.536 d      β^-    0.694, 1.99 ^47Sc
                                                  γ      1.297       -
                       ^48Ca 0.187%  >4×10^19 y   β^-β^-  ?          ^48Ti

                                                                References

   Calcium ( IPA: /ˈkalsiəm/) is the chemical element in the periodic
   table that has the symbol Ca and atomic number 20. It has an atomic
   mass of 40.078. Calcium is a soft grey alkaline earth metal, and is the
   fifth most abundant element in the Earth's crust. It is essential for
   living organisms, particularly in cell physiology, and is the most
   common metal in many animals. It may be used as a reducing agent in the
   extraction of thorium, zirconium and uranium.

Notable characteristics

   Calcium is a rather soft, gray, metallic element that 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.

   Calcium is essential in muscle contraction, oocyte activation, bones
   and tooth structure, blood clotting, nerve impulse transmission,
   regulating heartbeat, and fluid balance within cells. In the U.S.,
   between about 50% and 75% of adults do not get sufficient calcium in
   their diet. Adults need between 1,000 and 1,300 mg of calcium in their
   daily diet.

   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 3d 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

   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 Humphry 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.

Nutrition

   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;
   amaranth; collard greens; okra; rutabaga; broccoli; kale; and fortified
   products such as orange juice and soy milk. Calcium has also been found
   to assist in the production of lymphatic fluids.

   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. Adults need between 1,000 and 1,300 mg
   of calcium in their daily diet.

   Recommended Adequate Intake by the IOM for Calcium:

   Age------------------------Calcium (mg/day)

   0 to 6 months--------------210

   7 to 12 months-------------270

   1 to 3 years---------------500

   4 to 8 years---------------800

   9 to 13 years-------------1300

   14 to 18 years------------1300

   19 to 50 years------------1000

   51+ years-----------------1200

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

Dietary calcium supplements

   Calcium supplements are used to prevent and to treat calcium
   deficiencies. 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 because the percent of calcium absorbed
   decreases as the amount of calcium in the supplement increases. It is
   recommended to spread doses throughout the day, with the last dose near
   bedtime. Recommended daily calcium intake varies from 1000 to 1500 mg,
   depending upon the stage of life.

   In July 2006, a report citing research from Fred Hutchinson Cancer
   Research Centre in Seattle, Washington claimed that women in their 50's
   gained 5 pounds less in a period of 10 years by taking more than 500 mg
   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. It is recommended to take this supplement with
       food to aid in absorption. In some calcium supplements based on
       calcium carbonate, vitamin D is added to aid in absorption. Vitamin
       D is needed for the absorption of calcium from the stomach and for
       the functioning of calcium in the body.
     * 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 about 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

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