Magnesium
Magnesium (Mg) is an alkaline earth metal with atomic number 12 and an atomic mass of 24.305. Its electron configuration is [Ne] 3s2, which gives it 2 valence electrons.
Magnesium key data
| Symbol | Mg |
|---|---|
| Atomic number | 12 |
| Atomic mass (standard atomic weight) | 24.305 |
| Molar mass | 24.305 g/mol |
| Protons | 12 |
| Neutrons (most abundant isotope, magnesium-24) | 12 |
| Electrons (neutral atom) | 12 |
| Valence electrons | 2 |
| Category | Alkaline earth metal |
| Period | 3 |
| Group | 2 |
| Block | s-block |
| Noble gas notation | [Ne] 3s2 |
| Full electron configuration | 1s2 2s2 2p6 3s2 |
| Electrons per shell | 2, 8, 2 |
Atomic mass: IUPAC CIAAW abridged standard atomic weights, 2024. Most abundant isotope: NIST Atomic Weights and Isotopic Compositions.
The values are facts and free to use; this page’s selection and presentation are © 2026 ScienceQuest.
Measured properties of magnesium
From PubChem, the US National Institutes of Health. Public domain. PubChem’s periodic table gives no value for the rows not shown.
| Melting point | 923 K (649.85 °C), 66th of 103 by melting point |
|---|---|
| Boiling point | 1363 K (1089.9 °C), 67th of 93 by boiling point |
| Density | 1.74 g/cm³, 80th of 96 by density |
| State at room temperature | Solid |
| Electronegativity | 1.31 (Pauling), 60th of 95 by electronegativity |
| Van der Waals radius | 173 pm, 85th of 99 by atomic radius |
| First ionisation energy | 7.646 eV (737.7 kJ/mol), 40th of 102 by first ionisation energy |
| Common oxidation states | +2 |
| Discovered | 1808 |
Each rank counts down from the highest value, among the elements PubChem’s table gives one for, and links to that property ranked across the whole table. All of them are collected under periodic trends.
Magnesium electron configuration
The full electron configuration of magnesium is 1s2 2s2 2p6 3s2. With the noble-gas core collapsed it is [Ne] 3s2, and the outermost subshell is 3s2.
Why group and block follow from this is set out in how the periodic table maps electron configuration, and the electron configuration of every element is listed on one page.
Mass of one magnesium atom
A molar mass is grams per mole, so dividing by the Avogadro constant gives the mass of a single atom, or for an element with more than one natural isotope the average mass of its atoms, and the reciprocal gives how many atoms sit in a gram.
Mass of one atom
- one atom = 24.305 / (6.02214076 × 10²³)
- = 4.0359 × 10⁻²³ g
Atoms in one gram
- atoms per gram = 6.02214076 × 10²³ / 24.305
- = 2.4777 × 10²² atoms
Magnesium on the periodic table
Magnesium is in period 3, group 2, in the s-block.
The other elements of group 2 are beryllium, calcium, strontium, barium and radium.