Periodic Table


Atomic number: 20
Atomic weight: 40.078
Symbol: Ca
Group number: 2
Electronic configuration: [Ar].4s2


Calcium is a metallic element, fifth in abundance in the earth's crust, of which it forms more than 3%. It is an essential constituent of leaves, bones, teeth, and shells.

The metal is a silvery colour and is rather hard. Chemically it is one of the alkaline earth elements; it readily forms a white coating of nitride in air, reacts with water, burns with a yellow-red flame, forming largely the nitride.

Calcium does not occur free in nature. Calcium is found mostly as limestone, gypsum and fluorite. Stalagmites and stalactites contain calcium carbonate.

General information

Discoveror: Sir Humphrey Davy
Date discovered: 1808
Discovered at: England
Meaning of name: From the Latin word "calx" meaning "lime"

Physical data

Standard state: solid at 298 K
Colour: silvery white
Density of solid at ambient temperature/kg m-3: 1550
Molar volume/cm3: 26.20

Radii /pm

Atomic: 194
Covalent (single bond):
Pauling radius for the ion [Ca]-: no data

Valence shell orbital radius maxima (Rmax)
orbital s p d f
radius183.9no datano datano data


Both values are quoted on the Pauling scale.

Pauling: 1.00
Allred Rochow: 1.04

Crystal Structure

structure: ccp (cubic close-packed)

The following CrystalMaker image represents the solid state structure. For most elements, the most stable allotrope is illustrated. Try WebElements version 2 for interactive virtual reality and CHIME images.


Temperatures (/K)

melting point: 1115
boiling point: 1757

Enthalpies /kJ mol-1

fusion: 8.54
vaporization: 154.7

single bond enthalpies:
Ca-F Ca-Cl Ca-Br Ca-I Ca-Ca
550 429 402 326 46

Ionization enthalpies /kJ mol-1

Number Enthalpy


This section gives some data for naturally occurring isotopes.
Nominal mass Accurate mass % natural abundance
40Ca39.9625906 (13)96.941 (13)
42Ca41.9586176 (13)0.647 (3)
43Ca42.9587662 (13)0.135 (3)
44Ca43.9554806 (14)2.086 (5)
46Ca45.953689 (4)0.004 (3)
48Ca47.952533 (4)0.187 (3)

Further Information

Copyright 1997 Mark Winter
Department of Chemistry at the University of Sheffield, Sheffield S3 7HF, England.

The current version of this document is at http://www.shef.ac.uk/~chem/web-elements-I/Ca.html