Calcium (Ca)

Calcium is an alkaline earth metal with atomic number 20, in period 4 and group 2 of the periodic table. Its atomic mass is 40.078 u and its electron configuration is [Ar] 4s². Solid at 25 °C.

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Key facts

Atomic number	20
Atomic mass	40.078 u
Category	Alkaline Earth Metal
Period	4
Group	2
Block	s
Electron configuration	[Ar] 4s²
Electrons per shell	2, 8, 8, 2
Electronegativity (Pauling)	1
Oxidation states	+1, +2common in bold
State at 25 °C	Solid
Melting point	1115 K841.85 °C
Boiling point	1757 K1483.85 °C
Density	1.55 g/cm³

Atomic properties

First ionization energy	6.113 eV
Electron affinity	2.37 kJ/mol
Atomic radius	197 pm
Covalent radius	176 pm
Van der Waals radius	231 pm
Common ions	Ca²⁺
Protons, neutrons, electrons	20, 20, 20

Physical and thermal properties

Molar volume	26.2 cm³/mol
Heat of fusion	8.54 kJ/mol
Heat of vaporization	155 kJ/mol
Specific heat	631 J/(kg·K)
Thermal conductivity	200 W/(m·K)
Thermal expansion	2.23 × 10⁻⁵ K⁻¹
Mohs hardness	1.75
Young’s modulus	20 GPa
Crystal structure	Face-centered cubic
Magnetic type	Paramagnetic

Identification and history

CAS number	7440-70-2
Latin name	Calcium
Discovered by	Humphry Davy · 1808
Named by	---

Natural isotopes

Isotope	Mass (u)	Abundance
⁴⁰Ca	39.962591	96.941 %
⁴²Ca	41.958618	0.647 %
⁴³Ca	42.958766	0.135 %
⁴⁴Ca	43.955481	2.086 %
⁴⁶Ca	45.953688	0.004 %
⁴⁸Ca	47.952523	0.187 %

Data checked against PubChem (NIH), IUPAC, the NIST Atomic Spectra Database and the IAEA (NUBASE and AME), the same data you see in the app.

A dash (---) means there is no reliable published measurement. The app never makes one up.

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