Strontium (Sr)

Strontium is an alkaline earth metal with atomic number 38, in period 5 and group 2 of the periodic table. Its atomic mass is 87.62 u and its electron configuration is [Kr] 5s². Solid at 25 °C.

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Key facts

Atomic number	38
Atomic mass	87.62 u
Category	Alkaline Earth Metal
Period	5
Group	2
Block	s
Electron configuration	[Kr] 5s²
Electrons per shell	2, 8, 18, 8, 2
Electronegativity (Pauling)	0.95
Oxidation states	+1, +2common in bold
State at 25 °C	Solid
Melting point	1050 K776.85 °C
Boiling point	1655 K1381.85 °C
Density	2.63 g/cm³

Atomic properties

First ionization energy	5.695 eV
Electron affinity	5.03 kJ/mol
Atomic radius	215 pm
Covalent radius	195 pm
Van der Waals radius	249 pm
Common ions	Sr²⁺
Protons, neutrons, electrons	38, 50, 38

Physical and thermal properties

Molar volume	33.94 cm³/mol
Heat of fusion	8 kJ/mol
Heat of vaporization	137 kJ/mol
Specific heat	300 J/(kg·K)
Thermal conductivity	35 W/(m·K)
Thermal expansion	2.25 × 10⁻⁵ K⁻¹
Mohs hardness	1.5
Young’s modulus	15.7 GPa
Crystal structure	Face-centered cubic
Magnetic type	Paramagnetic

Identification and history

CAS number	7440-24-6
Latin name	Strontium
Discovered by	William Cruickshank · 1787
Named by	---

Natural isotopes

Isotope	Mass (u)	Abundance
⁸⁴Sr	83.913419	0.56 %
⁸⁶Sr	85.909261	9.86 %
⁸⁷Sr	86.908877	7 %
⁸⁸Sr	87.905612	82.58 %

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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