Magnesium (Mg)
Element 12 · Alkaline earth metal · atomic mass 24.305 u · group 2, period 3
Electron shells: 2, 8, 2
Magnesium is the lightest structural metal, about a third lighter than aluminium. It sits at the centre of every chlorophyll molecule, which is why plants are green.
Burning magnesium is so hot it keeps burning underwater, pulling oxygen straight out of H₂O.
- Atomic number
- 12
- Atomic mass
- 24.305 u
- Electron configuration
- [Ne] 3s²
- Group · period · block
- 2 · 3 · s
- Oxidation states
- +2
- Electronegativity
- 1.31 (Pauling)
- Melting point
- 650 °C
- Boiling point
- 1,090 °C
- Density
- 1.74 g/cm³
- State at 20 °C
- Solid
- Appearance
- Shiny grey metal
- Discovered
- Joseph Black; isolated by Humphry Davy, 1808
12 protons, and 12 electrons when neutral
IUPAC interval [24.304, 24.307]
Alkaline earth metals
What Magnesium is used for
- Lightweight alloys for cars and laptops
- Flares and fireworks
- Dietary supplements and antacids
- Removing sulphur from steel
Atomic structure of Magnesium
A neutral magnesium atom has 12 protons and 12 electrons. Its most common isotope carries about 12 neutrons, which is where the mass number 24 comes from. Change the neutron count and you have a different isotope of magnesium; change the proton count and you have a different element entirely.
Those electrons fill shells from the inside out: 2, 8, 2. In orbital notation that is [Ne] 3s², leaving 2 valence electrons in the outer shell — the ones that do the chemistry.
3D electron orbitals
See where Magnesium's electrons actually are — a cloud of 26,000 points sampled from the probability density |ψ|², not a cartoon of a lobe.
Where Magnesium sits in the periodic table
Group 2 metals with two outer electrons. Harder and less reactive than the alkali metals, and they form the +2 ions that build bone, shell and cement.
Discovery and naming
Magnesium was discovered by Joseph Black; isolated by Humphry Davy in 1808. Its name comes from Magnesia, a district of Thessaly, which is also why its symbol (Mg) does not match its English name.
Keep exploring
Atomic weight from IUPAC/CIAAW; physical properties from PubChem (US National Library of Medicine). Values that have never been measured are shown as “not measured” rather than estimated.
Related Calculators
Frequently Asked Questions
What is the atomic mass of Magnesium?
The standard atomic weight of Magnesium is 24.305 u. Because the natural isotope mix varies between sources, IUPAC publishes it as the interval [24.304, 24.307], and 24.305 is the conventional single value to use in calculations.
How many protons, neutrons and electrons does Magnesium have?
Magnesium has 12 protons, because the atomic number is the proton count and that is what makes an atom Magnesium at all. A neutral Magnesium atom has the same number of electrons, 12. The neutron count varies by isotope; the most common one has about 12, since 24 − 12 = 12.
What is the electron configuration of Magnesium?
The electron configuration of Magnesium is [Ne] 3s². Its electrons are arranged 2, 8, 2 across 3 shells.
Is Magnesium a metal?
Yes. Magnesium is classified as a alkaline earth metal, on the left side of the table.
What group and period is Magnesium in?
Magnesium is in group 2 (the alkaline earth metals), period 3, in the s-block. The group is its column and the period is its row.
What is the charge of Magnesium?
Magnesium most commonly forms a 2+ ion. It has 2 electrons in its outer shell and loses them readily, which is what the group number tells you.
What is the melting point of Magnesium?
Magnesium melts at 650 °C and boils at 1,090 °C. That puts it in the solids at everyday temperatures.
What is Magnesium used for?
Lightweight alloys for cars and laptops, Flares and fireworks, Dietary supplements and antacids, Removing sulphur from steel. Magnesium is the lightest structural metal, about a third lighter than aluminium.
Who discovered Magnesium, and where does its name come from?
Magnesium (Mg) was discovered by Joseph Black; isolated by Humphry Davy in 1808. The name comes from Magnesia, a district of Thessaly.