Calcium
[Ar] 4s² · 2 · 8 · 8 · 2
The metal that bones, shells, coral reefs and limestone mountains are built from. Calcium is the fifth most abundant element in the crust and the principal structural material of the living world.
3D model
Bohr model: nucleus and electron shells from the real configuration. Valence electrons are highlighted.
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Atomic properties
- Atomic number
- 20
- Atomic mass
- 40.078 а.е.м.
- Electron configuration
- [Ar] 4s²
- Electrons per shell
- 2 · 8 · 8 · 2
- Block
- s-block
- Group
- Alkaline earth metals
- Period
- 4
- Electronegativity (Pauling)
- 1
- Electronegativity (Allen)
- 1.03
- Atomic radius
- 194 pm
- Covalent radius
- 176 pm
- Van der Waals radius
- 231 pm
- Ionisation energy 1
- 589.8 kJ/mol
- Ionisation energy 2
- 1 145.4 kJ/mol
- Ionisation energy 3
- 4 912.4 kJ/mol
- Ionisation energy 4
- 6 491 kJ/mol
- Ionisation energy 5
- 8 153 kJ/mol
- Electron affinity
- 2.37 kJ/mol
- Common oxidation states
- +2
- Oxidation states
- +1, +2
Physical properties
- State at 25 °C
- solid
- Density
- 1.55 g/cm³
- Melting point
- 1 115 K · 841.9 °C
- Boiling point
- 1 757 K · 1 483.9 °C
- Speed of sound
- 3 810 m/s
Thermal properties
- Heat of fusion
- 8.54 kJ/mol
- Heat of vaporisation
- 154.7 kJ/mol
- Specific heat capacity
- 0.647 J/(g·K)
- Thermal conductivity
- 201 W/(m·K)
Mechanical properties
- 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
Electrical and magnetic properties
- Electrical resistivity
- 33.6 nΩ·m
- Magnetic ordering
- paramagnetic
- Curie point
- no data
- Néel point
- no data
- Superconducting point
- no data
Crystal structure
- Crystal structure
- face-centred cubic (fcc)
- Lattice constants
- a = 558.84 pm
Abundance
- In the crust
- 41 500 mg/kg
- In the ocean
- 412 mg/L
- In the universe
- 70 000 mg/kg
- In the human body
- 14 000 mg/kg
Isotopes
| Isotope | Abundance | Half-life | Decay mode |
|---|---|---|---|
| 40Ca | 96.941 % | stable | — |
| 42Ca | 0.647 % | stable | — |
| 43Ca | 0.135 % | stable | — |
| 44Ca | 2.086 % | stable | — |
| 46Ca | 0.004 % | stable | — |
| 48Ca | 0.187 % | stable | — |
Calcium-48 is among the most neutron-rich stable nuclides, and it is the beam that bombarded targets to make elements 113 through 118.
Discovery
- Year of discovery
- 1808
- Discovered by
- Humphry Davy
- Where
- England
- Origin of the name
- from Latin calx (lime)
History
Lime had been a building material for millennia, but Davy isolated the metal in 1808 by electrolysing a mixture of lime and mercuric oxide. The name is from Latin calx, lime.
Where it occurs
41 500 mg/kg of the crust. The main minerals are calcite and aragonite — limestone, marble, chalk — plus gypsum and fluorite. The white cliffs of Dover are compacted shells of ancient algae.
How it is produced
Calcium metal comes from aluminothermic reduction of lime in vacuum. But the overwhelming bulk of production is limestone, simply crushed or calcined.
Role in living things
About 1.4 % of body mass, 99 % of it in the skeleton. The remaining one per cent runs muscle contraction, blood clotting and intracellular signalling; cytoplasmic calcium is regulated to ten-thousandths of a millimole.
Safety
Calcium metal reacts with water and calcium oxide causes severe alkali burns. Dietary calcium salts are safe; excess is simply absorbed poorly.
Uses
- Cement and lime — the foundation of the whole construction industry
- Deoxidiser and desulfuriser in steelmaking
- Liming acid soils in agriculture
- Gypsum for plaster and for medical casts
Curiosities
- A calcium-48 beam at Dubna produced five new elements of the table.
- Calcium colours a flame brick red.
- Limestone, marble and chalk are the same substance with different histories.
- Lime mortar sets by absorbing carbon dioxide from the air and returning to carbonate — a cycle that closes over centuries.