012Alkaline earth metal · Group 2 · Period 3

Magnesium

Magnesium (Mg) is element 12, a alkaline earth metal in the s-block — group 2, period 3. It is a solid at room temperature with 3 electron shells (2, 8, 2) and an atomic mass of 24.305 u.

Atomic mass: 24.30 u
Phase · STP: solid
Melting: 923 K · 650 °C
Boiling: 1363 K · 1090 °C
Electronegativity: 1.31
Density: 1.738 g/cm³

Photograph — Warut Roonguthai, CC BY-SA 3.0 <https://creativecommons.org/licenses/by-sa/3.0>, via Wikimedia Commons

Emission spectrum

The visible light Magnesium emits when energised — its unique spectral fingerprint.

Identity

Atomic number: 12
Standard atomic weight: 24.30 u
Category: Alkaline earth metal
Group: 2 · Alkaline earth metals
Period: 3
Block: s-block
Oxidation states: +2

Physical properties

Melting point: 923 K · 650 °C
Boiling point: 1363 K · 1090 °C
Density: 1.738 g/cm³
Molar heat capacity: 24.869 J/(mol·K)
Atomic radius: 173 pm
Electron affinity: -40 kJ/mol

Atomic structure

12protons

12neutrons

12electrons

2valence e⁻

Noble-gas notation: [Ne] 3s2
Full configuration: 1s2 2s2 2p6 3s2
Electrons per shell: 2, 8, 2

Periodic trends

Where Magnesium ranks across all 118 elements.

Electronegativity1.31

Ionization energy737.7 kJ/mol

Electron affinity-40 kJ/mol

Density1.738 g/cm³

Atomic radius173 pm

Ionization energies

Energy to remove each successive electron (kJ/mol).

737.7

1.5k

7.7k

10.5k

13.6k

18.0k

21.7k

25.7k

31.7k

35.5k

Successive ionization energies (kJ/mol, log scale).

Discovery

Discovered: 1808
Discovered by: Joseph Black
Named by: —
Appearance: shiny grey solid