Calcium (Ca)

Stable isotopes of calcium available from ISOFLEX

Isotope Z(p) N(n) Atomic Mass Natural Abundance Enrichment Level Chemical Form
Ca-40 20 20 39.9625912 96.941% 99.99% Carbonate
Ca-42 20 22 41.9576183 0.647% 68.00-96.80% Carbonate
Ca-43 20 23 42.958767 0.135% 62.20-90.00% Carbonate
Ca-44 20 24 43.955481 2.086% 94.50-99.00% Carbonate
Ca-46 20 26 45.953693 0.004% 15.90-24.80% Carbonate
Ca-48 20 28 47.952533 0.187% 64.00-97.10% Carbonate

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Calcium was discovered in 1808 by Sir Humphry Davy. Its name originates with the Latin word calx, meaning “lime.” Compounds such as lime were prepared by the Romans as early as the first century AD. Literature dating back to 975 AD indicates that plaster of Paris (calcium sulfate) is useful for setting bones. 

A moderately soft, bright silver-white, crystalline metal, calcium oxidizes in air to form adherent protective film and can be machined, extruded or drawn. It is soluble in acid and decomposes in water to liberate hydrogen. It has a brick-red color when introduced to flame in a flame test.

Calcium metal reacts with a number of nonmetallic elements, forming their corresponding binary compounds. While the reaction with fluorine occurs at ambient temperatures, other elements combine only at elevated temperatures in the range of 300-900 ºC. Calcium reacts vigorously with water at ordinary temperatures, with the evolution of hydrogen. It is a strong reducing agent and can reduce most metal oxides and halides into their metals at elevated temperatures. It can reduce all the lower electropositive metals.

Applications of calcium are mostly found in metallurgy. It is used to produce alloys with aluminum, lead, beryllium, copper, silicon and other metals. It is also used as a desulfurizer, decarburizer and deoxidizer for ferrous and nonferrous alloys; for removal of bismuth from lead; and as a reducing agent for zirconium, uranium, thorium and other metals.

Properties of Calcium

Name Calcium
Symbol Ca
Atomic number 20
Atomic weight 40.078
Standard state Solid at 298 °K
CAS Registry ID 7440-70-2 
Group in periodic table 2
Group name Alkaline earth metal 
Period in periodic table
Block in periodic table s-block 
Color Silvery white
Classification Metallic
Melting point 851 °C
Boiling point 1484 °C
Thermal conductivity 200 W/(m·K)
Electrical resistivity 3.43 µΩ·cm at 0 °C
Electronegativity 1.0 
Specific heat 0.647 J/g·K at 20 °C
Heat of vaporization 155 kJ·mol-1
Heat of fusion 8.54 kJ·mol-1
Density of solid 1.54 g/cm3
Electron configuration [Ar]4s2
Ionic radius  1.06 Å (Ca2+
Oxidation state +2 
Standard electrode potential  Eº = -2.87V 

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