ElementsWhat is magnesium?
Magnesium is a light, silvery metal that burns with a very bright white flame. It is common in rocks and sea water, and the green colour of plants comes from chlorophyll, which contains it.
What is magnesium used for?
Light alloys for cars, aircraft and laptops, fireworks and flares, and antacids and other medicines made from its compounds.
Where the name comes from
From Magnesia, a district in Greece where its minerals were found.
Key facts
- Symbol
- Mg
- Atomic number
- 12
- Atomic mass
- 24.305 u
- Family
- Alkaline earth metal
- Period
- 3
- Group
- 2
- Block
- s
- State at room temperature
- Solid
- Melting point
- 649.9 °C (923 K, 1,202 °F)
- Boiling point
- 1,090 °C (1,363 K, 1,994 °F)
- Density
- 1.74 g/cm³
- Electrons per shell
- 2, 8, 2
- Electron configuration
- [Ne]3s2
- Common oxidation states
- +2
- Electronegativity (Pauling)
- 1.31
- First ionisation energy
- 7.646 eV
- Electron affinity
- no value
- Atomic radius (van der Waals)
- 173 pm
- Discovered
- 1808
Place in the periodic table
Magnesium is element number 12. It sits in period 3 (row 3) of the periodic table, in group 2 (column 2), and belongs to the s-block. Just before it comes sodium (11), and just after it comes aluminium (13). In the same column, beryllium is above it and calcium is below it. Elements in one column tend to behave alike.
Family: Alkaline earth metals.
Physical properties
At room temperature magnesium is a solid. It melts at 649.9 °C and boils at 1,090 °C, so it stays liquid over a range of 440 degrees. Its density is 1.74 grams per cubic centimetre, so a one-litre block would weigh about 1.74 kilograms. By density it ranks 80th among the 96 elements with a measured value.
Inside the atom
An atom of magnesium has 12 protons in its nucleus and, when neutral, 12 electrons around it. The electrons are arranged in 3 shells: 2, 8, 2. The outermost shell holds 2 electrons. Written in full, the electron configuration is [Ne]3s2.
Its electronegativity on the Pauling scale is 1.31. This number shows how strongly an atom pulls shared electrons towards itself: fluorine, the strongest, is 3.98. Removing one electron from an atom takes 7.646 electronvolts (about 738 kilojoules per mole). One mole of magnesium weighs 24.305 grams, so a single gram contains about 2.48 × 1022 atoms.
The ring picture is a simple model that only counts the electrons in each shell. Real atoms do not look like this.
Next steps
- Work out the weight of a compound that contains magnesium with the molar mass calculator.
- Compare it with every other element in the sortable list.
- Test yourself with the symbol quiz.
Figures on this page are from PubChem (U.S. National Library of Medicine), as downloaded on 11 November 2026. See About and data sources.