Magnesium Facts

Magnesium is the twelfth element of the periodic table. These magnesium facts contain chemical and physical data along with general information and history.

Element cell for Magnesium

Magnesium periodic table tile

Basic Magnesium Facts

Name: Magnesium

Atomic Number: 12

Element Symbol: Mg

Group: 2

Period: 3

Block: s

Element Family: alkaline earth

Atomic Mass: [24.304, 24.307]
IUPAC guidelines to reflect the physical and chemical history of the magnesium sample. If a single value of the atomic mass is needed, use 24.305.

Electron Configuration: [Ne]3s2 (shorthand) or 1s22s22p63s2 (full)

Discovery: Joseph Black in 1755 identified magnesium as an element. Sir Humphrey Davy isolated pure magnesium in 1808.

Many chemists believed lime (calcium oxide) and magnesia (magnesium oxide) were the same substance. Both were produced by heating limestone and magnesite. Black showed they each had different chemical properties. Magnesia contained an unknown element similar to calcium. Just over 50 years later, Davy separated magnesium from an amalgam of magnesia and mercury using electrolysis.

Name Origin: Davy named the element after its source material, magnesia.


Natural magnesium is comprised of three stable isotopes: 24Mg, 25Mg and 26Mg. Nineteen radioactive isotopes have been produced under laboratory conditions ranging from 19Mg to 40Mg.

Magnesium-24 is a stable isotope containing 12 neutrons. 78.99% of natural magnesium is magnesium-24.

Magnesium-25 is a stable isotope containing 13 neutrons. 10% of natural magnesium is magnesium-25.

Magnesium-26 is a stable isotope containing 14 neutrons. 11.01% of natural magnesium is magnesium-26.

Crystallized Magnesium

Chunk of crystallized magnesium. Credit: CSIRO, Mark Fergus/Creative Commons)

Physical Data

Density: 1.74 g/cm3

Melting Point: 923 K ​(650 °C, ​1202 °F)

Boiling Point: 1363 K ​(1091 °C, ​1994 °F)

State at 20ºC: Solid

Heat of Fusion: 8.48 kJ/mol

Heat of Vaporization: 128 kJ/mol

Molar Heat Capacity: 24.869 J/mol·K

Magnesium Atom

Electron shell configuration of a magnesium atom.

Atomic Data

Atomic Radius: 1.6 Å

Covalent Radius: 1.41 Å

Van der Waals Radius:  1.73 Å

Electron Affinity: not stable

Electronegativity: 1.31

1st Ionization Energy: 737.75 kJ/mol

2nd Ionization Energy: 1450.683 kJ/mol

3rd Ionization Energy: 7732.692 kJ/mol

4th Ionization Energy: 10542.519 kJ/mol

5th Ionization Energy: 13630.48 kJ/mol

6th Ionization Energy: 18019.6 kJ/mol

7th Ionization Energy: 21711.13 kJ/mol

8th Ionization Energy: 25661.24 kJ/mol

Oxidation States: +2 (common), +1 (uncommon)

Fun Magnesium Facts

  • Magnesium is a silvery-white alkaline solid at room temperature.
  • Magnesium has a sour taste. Small amounts of magnesium in mineral water gives it that slightly sour flavor.
  • An early name for magnesium was “magnium”. The metallic form of manganese was already known as magnesium. Davy was convinced by his colleagues to change the name to magnesium and manganese metal was just called manganese.
  • Magnesium is a central atom in the chlorophyll molecule. It is an essential part of the process of photosynthesis.
  • Magnesium is the ninth most abundant element in the universe.
  • Magnesium is the eighth most abundant element in the Earth’s crust.
  • Magnesium is the 11th most abundant element in the human body. There is magnesium in every one of your cells.
  • 60% of the magnesium found in your body is found in your skeletal system.
  • Magnesium burns very brightly and is used in fireworks to make white sparkles.
  • Magnesium is added to alloys to reduce weight of aluminum materials.
  • Magnesium is found in some firestarters to produce sparks when rubbed with steel.
  • Magnesium hydroxide is added to some plastics to make them fire resistant.
  • A class of organic magnesium compounds known as Grignard reagents are important compounds in synthesis reactions in organic chemistry. These compounds take the form: RMg-X, where R is a carbon functional group and X is a halide.

Learn more about elements on the periodic table.

Magnesium Facts
Last modified: May 26th, 2015 by Todd Helmenstine

2 thoughts on “Magnesium Facts

    1. Anne Helmenstine

      Magnesium grows metal crystals that somewhat resemble little conifer trees, but usually it’s seen as what you think of as a normal metal — smooth and shiny. Like the other alkaline earths, it forms an oxide layer, which makes it dull and less-smooth.

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