Calcium

Calcium is a chemical      Potassium - Calcium - Scandium
element in the periodic
table that has the symbol  Mg
Ca and atomic number 20.   Ca
Calcium is a soft grey     SrÊÊ [Image:Ca-TableImage.png]
alkaline earth metal that  Ê           Full table
is used as a reducing      Ê

agent in the extraction of                      General
thorium, zirconium and
uranium. This element is   Name, Symbol, Number      Calcium, Ca, 20
also the fifth most        Series                    Alkaline earth metal
abundant element in the    Group, Period, Block      2 (IIA), 4, s
earth's crust and is an
essential element for      Density, Hardness         1550 kg/m3, 1.75
living organisms.          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

Notable Characteristics    Oxidation states (Oxide)  2 (strong base)
Calcium is a rather hard   Crystal structure         Cubic face centered
element that is purified                  Physical Properties
by electrolysis from       State of matter           solid (paramagnetic)
calcium fluoride that
burns with a yellow-red    Melting point             1115 K (1548¡F)
flame and forms a white    Boiling point             1757 K (2703¡F)
nitride coating when
exposed to air. It reacts  Molar volume              26.20 ×103 m3/mol
with water displacing      Heat of vaporization      153.6 kJ/mol
hydrogen and forming       Heat of fusion            8.54 kJ/mol
calcium hydroxide.
                           Vapor pressure            254 Pa at 1112 K
Applications               Speed of sound            3810 m/s at 293.15 K
Calcium is an important                          Other
component of a healthy     Electronegativity         1.00 (Pauling scale)
diet. Its minor deficit    Specific heat capacity    0.632 J/(kg*K)
can affect bone and teeth
formation. Its excess can  Electrical conductivity   29.8 106/m ohm
lead to kidney stones.     Thermal conductivity      201 W/(m*K)
Vitamin D is needed to
absorb calcium. Dairy      1st ionization potential  589.8 kJ/mol

products are an excellent  2nd ionization potential  1145.4 kJ/mol
source of calcium. Other
uses include:              3rd ionization potential  4912.4 kJ/mol

   * Reducing agent in the               Most Stable Isotopes

     extraction of other    iso    NA     half-life       DM    DE MeV  DP
     metals such as
     uranium, zirconium,   40Ca 96.941% Ca is stable with 20 neutrons

     and thorium.          41Ca {syn.}  103,000y        epsilon 0.421  41K
   * Deoxidizer,
     desulfurizer, or      42Ca 0.647%  Ca is stable with 22 neutrons

     decarburizer for      43Ca 0.135%  Ca is stable with 23 neutrons
     various ferrous and
     nonferrous alloys.    44Ca 2.086%  Ca is stable with 24 neutrons
   * Alloying agent used
     in the production of  46Ca 0.004%  Ca is stable with 26 neutrons

     aluminum, beryllium,  48Ca 0.187%  >6×1018y  beta-   4.272  48Ti
     copper, lead, and
     magnesium alloys.        SI units & STP are used except where noted.

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. 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.

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