Alkaline earth metalElement 12 · s-block

Magnesium (Mg)

Magnesium (Mg) is an alkaline earth metal with atomic number 12 and a standard atomic weight of 24.305. At room temperature it is a solid that melts at 650 °C and boils at 1,090 °C.

12MgMagnesium24.305

Atomic number

protons

Atomic weight

24.305

CIAAW 2024

Melting point

650 °C

923.15 K

Boiling point

1,090 °C

1,363.15 K

Density

1.74 g/cm³

near room temperature

Electronegativity

1.31

Pauling scale

State at 25 °C

Solid

Discovered

1808

England

Magnesium at a glance

Identity

Symbol	Mg
Atomic number (Z)	12
Atomic weight	24.305 ± 0.002 (CIAAW 2024)
Category	Alkaline earth metal
Group	2 — alkaline earth metals
Period	3
Block	s-block
CAS number	7439-95-4

Atomic properties

Electron configuration	[Ne] 3s² Full: 1s² 2s² 2p⁶ 3s²
Electrons per shell	2, 8, 2
Oxidation states	+2 Less common: 0, +1
Electronegativity (Pauling)	1.31
First ionisation energy	7.646 eV (737.7 kJ/mol) 2nd: 15.035 eV · 3rd: 80.144 eV
Atomic radius (empirical)	150 pm
Covalent radius	139 pm
Van der Waals radius	173 pm

Physical properties

State at 25 °C	Solid
Melting point	650 °C · 1,202 °F · 923.15 K
Boiling point	1,090 °C · 1,994 °F · 1,363.15 K
Density	1.74 g/cm³
Specific heat capacity	1.023 J/(g·K)
Thermal conductivity	156 W/(m·K)
Crystal structure	Hexagonal

Isotopes & abundance

Natural occurrence	Primordial
Radioactive	No
Natural isotopes (abundance)	²⁴Mg 78.965%, ²⁶Mg 11.025%, ²⁵Mg 10.011%
Stable isotopes	5
Known isotopes	23
Abundance in Earth's crust	23,300 mg/kg
Abundance in seawater	1,290 mg/L

Atomic weights: CIAAW Abridged Standard Atomic Weights 2024. Other properties: standard reference compilations, checked October 2026; predicted values are marked.

Magnesium electron configuration

Magnesium has 12 electrons. Written in short form, its ground-state configuration is [Ne] 3s² — the electrons of the noble gas neon, plus 3s².Written out in full: 1s² 2s² 2p⁶ 3s².

As a member of group 2 it has 2 valence electrons in its outer shell (shell 3), which largely decide its chemistry.

3s↑↓

Discovery and name

Discovered

1808 — Humphry Davy (recognised as an element by Joseph Black, 1755) · England.

Name

From Magnesia, a district in Thessaly, Greece.

Known for

A light structural metal used in alloys for cars, aircraft and laptops. Every chlorophyll molecule has a magnesium ion at its centre.

Isotopes of magnesium

Naturally occurring magnesium is a mix of 3 isotopes. Each has 12 protons; they differ in the number of neutrons:

Isotope	Protons	Neutrons	Natural abundance	Stability
²⁴Mg	12	12	78.965%	stable
²⁶Mg	12	14	11.025%	stable
²⁵Mg	12	13	10.011%	stable

23 isotopes of magnesium are known in our data set (half-lives as published in nuclear data tables).

Magnesium compared with group 2

The other elements in group 2 (alkaline earth metals), from top to bottom of the table:

Element	Z	Atomic weight	Melting point	Boiling point	Density	Electronegativity
Beryllium	4	9.0122	1,287 °C	2,468 °C	1.85 g/cm³	1.57
Magnesium	12	24.305	650 °C	1,090 °C	1.74 g/cm³	1.31
Calcium	20	40.078	842 °C	1,484 °C	1.54 g/cm³	1
Strontium	38	87.62	777 °C	1,377 °C	2.64 g/cm³	0.95
Barium	56	137.33	727 °C	1,845 °C	3.51 g/cm³	0.89
Radium	88	[226]	696 °C	1,737 °C	5 g/cm³	0.9

Frequently asked questions

6 answers

What is the atomic mass of magnesium?

The standard atomic weight of magnesium is 24.305 ± 0.002 (CIAAW 2024), so one mole weighs about 24.305 grams.

How many protons, neutrons and electrons does magnesium have?

A neutral magnesium atom has 12 protons and 12 electrons. Its most common isotope, magnesium-24, has 12 neutrons.

What is the electron configuration of magnesium?

[Ne] 3s² (in full: 1s² 2s² 2p⁶ 3s²).

What are the melting and boiling points of magnesium?

Magnesium melts at 650 °C (1,202 °F) and boils at 1,090 °C (1,994 °F).

Is magnesium a metal?

Magnesium is a metal. It is in group 2, period 3, and is a solid at room temperature.

Who discovered magnesium?

1808 — Humphry Davy (recognised as an element by Joseph Black, 1755) (England).