calcium

Calcium, ₂₀Ca
Calcium
Appearance	dull gray, silver; with a pale yellow tint
Standard atomic weight Ar°(Ca)
Calcium in the periodic table
	potassium ← calcium → scandium
Atomic number (Z)	20
Group	group 2 (alkaline earth metals)
Period	period 4
Block	s-block
Electron configuration	[Ar] 4s2
Electrons per shell	2, 8, 8, 2
Physical properties
Phase at STP	solid
Melting point	1115 K (842 °C, 1548 °F)
Boiling point	1757 K (1484 °C, 2703 °F)
Density (at 20° C)	1.526 g/cm3
when liquid (at m.p.)	1.378 g/cm3
Heat of fusion	8.54 kJ/mol
Heat of vaporization	154.7 kJ/mol
Molar heat capacity	25.929 J/(mol·K)
Atomic properties
Oxidation states	common: +2; +1
Electronegativity	Pauling scale: 1.00
Ionization energies	1st: 589.8 kJ/mol ; 2nd: 1145.4 kJ/mol ; 3rd: 4912.4 kJ/mol ; (more) ;
Atomic radius	empirical: 197 pm
Covalent radius	176±10 pm
Van der Waals radius	231 pm
	Spectral lines of calcium
Other properties
Natural occurrence	primordial
Crystal structure	face-centered cubic (fcc) (cF4)
Lattice constant	a = 558.8 pm (at 20 °C)
Thermal expansion	22.27×10−6/K (at 20 °C)
Thermal conductivity	201 W/(m⋅K)
Electrical resistivity	33.6 nΩ⋅m (at 20 °C)
Magnetic ordering	diamagnetic
Molar magnetic susceptibility	+40.0×10−6 cm3/mol
Young's modulus	20 GPa
Shear modulus	7.4 GPa
Bulk modulus	17 GPa
Speed of sound thin rod	3810 m/s (at 20 °C)
Poisson ratio	0.31
Mohs hardness	1.75
Brinell hardness	170–416 MPa
CAS Number	7440-70-2
History
Naming	from the Latin word for lime, calx
Discovery and first isolation	Humphry Davy (1808)
Isotopes of calcium v; e;
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