ca mass number


Isotope Atomic mass (Da) Isotopic abundance (amount fraction)
40 Ca 39.962 5909(2) 0.969 41(156)
42 Ca 41.958 618(1) 0.006 47(23)
43 Ca 42.958 766(2) 0.001 35(10)
44 Ca 43.955 482(2) 0.020 86(110)
46 Ca 45.953 69(2) 0.000 04(3)
48 Ca 47.952 5229(6) 0.001 87(21)

In 1983, the Commission with its liberalized policy on uncertainties, was able to recommend as standard atomic weight Ar(Ca) = 40.078(4) weighted toward the mass-spectrometric measurements. Moreover, the stated uncertainty includes all chemical, x-ray, and mass-spectrometric measurements believed to be significant by the Commission, as enumerated in its 1983 report.

There is evidence for minor isotope fractionation of calcium in Nature, causing variability of Ar(Ca) in normal sources that is within the uncertainty of the standard atomic weight. Variations in n( 44 Ca)/n( 40 Ca) can be reported as δ 44 Ca values relative to the calcium carbonate reference material NIST-SRM 915a. A recent compilation yielded a range of published δ 44 Ca values in natural samples from a low of -2.17 ‰ in a cougar bone with Ar(Ca) = 40.0778 to a high of +2.76 ‰ in egg white with Ar(Ca) = 40.0784. Elemental calcium with as δ 44 Ca = -6.0 ‰ (Ar(Ca) = 40.0773) also has been reported. Variations in the isotopic composition of marine calcium have occurred over the last 80 Ma.

In addition, there are many reports of anomalous isotopic composition of some minor samples of Ca, some of which may have arisen from the decay of 40 K to 40 Ca. The annotation “g” is therefore maintained for this element. 41 Ca is an extinct radioisotope (with a half-life of 0.1 Ma), which can be used to date the early history of the solar system through its decay to 41 K.

SOURCE Atomic weights of the elements: Review 2000 by John R de Laeter et al. Pure Appl. Chem. 2003 (75) 683-800
© IUPAC 2003

Ar(Ca) = 40.078(4) since 1983

The name derives from the Latin calx for “lime” (CaO) or “limestone” (CaCO3) in which it was found. It was first isolated by British chemist Humphry Davy in 1808 with help from the Swedish chemist Jöns Jacob Berzelius and the Swedish court physician M. M. af Pontin.

Calcium Isotope Atomic mass (Da) Isotopic abundance (amount fraction) 40 Ca 39.962 5909(2) 0.969 41(156) 42 Ca 41.958 618(1) 0.006 47(23) 43 Ca 42.958 766(2) 0.001

Ca mass number


Specific heat capacity (J kg −1 K −1 )

Specific heat capacity is the amount of energy needed to change the temperature of a kilogram of a substance by 1 K.

Young’s modulus

A measure of the stiffness of a substance. It provides a measure of how difficult it is to extend a material, with a value given by the ratio of tensile strength to tensile strain.

Shear modulus

A measure of how difficult it is to deform a material. It is given by the ratio of the shear stress to the shear strain.

Bulk modulus

A measure of how difficult it is to compress a substance. It is given by the ratio of the pressure on a body to the fractional decrease in volume.

Vapour pressure

A measure of the propensity of a substance to evaporate. It is defined as the equilibrium pressure exerted by the gas produced above a substance in a closed system.

Pressure and temperature data – advanced

Pressure and temperature data – advanced



Chemistry in its element: calcium





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Element Calcium (Ca), Group 2, Atomic Number 20, s-block, Mass 40.078. Sources, facts, uses, scarcity (SRI), podcasts, alchemical symbols, videos and images.