Magnesium Facts (Mg or Atomic Number 12)

Magnesium Chemical & Physical Properties

Magnesium facts
Magnesium is an alkaline earth metal.

Malachy120 / Getty Images

Magnesium is an element that is essential for human nutrition. This alkaline earth metal has atomic number 12 and element symbol Mg. The pure element is a silver-colored metal, but it tarnishes in air to give it a dull appearance.

Magnesium crystals
Crystals of pure magnesium metal. Lester V. Bergman / Getty Images

Magnesium Basic Facts

Atomic Number: 12

Symbol: Mg

Atomic Weight: 24.305

Discovery: Recognized as an element by Black 1775; Isolated by Sir Humphrey Davy 1808 (England). Magnesium first came into use as magnesium sulfate or Epsom salt. The story goes that in 1618 a farmer in Epsom, England could not get his cattle to drink from a well with bitter-tasting water, yet the water seemed to heal skin conditions. The substance in the water (magnesium sulfate) came to be known as Epsom salts.

Electron Configuration: [Ne] 3s2

Word Origin: Magnesia, a district in Thessaly, Greece (Davy initially suggested the name magnium.)

Properties: Magnesium has a melting point of 648.8°C, boiling point of 1090°C, specific gravity of 1.738 (20°C), and valence of 2. Magnesium metal is light (one-third lighter than aluminum), silvery-white, and relatively tough. The metal tarnishes slightly in air. Finely divided magnesium ignites upon heating in air, burning with a bright white flame.

Uses: Magnesium is used in pyrotechnic and incendiary devices. It is alloyed with other metals to make them lighter and more easily welded, with applications in the aerospace industry. Magnesium is added to many propellents. It is used as a reducing agent in the preparation of uranium and other metals that are purified from their salts. Magnesite is used in refactories. Magnesium hydroxide (milk of magnesia), sulfate (Epsom salts), chloride, and citrate are used in medicine. Organic magnesium compounds have many uses. Magnesium is essential for plant and animal nutrition. Chlorophyll is a magnesium-centered porphyrin.

Biological Role: All known living cells require magnesium for nucleic acid chemistry. In humans, over 300 enzymes use magnesium as a catalyst. Foods rich in magnesium include nuts, cereals, cocoa beans, green leafy vegetables, and some spices. The average adult human body contains 22 to 26 grams of magnesium, mostly in the skeleton and skeletal muscles. Magnesium deficiency (hypomagnesemia) is common and occurs in 2.5 to 15% of the population. Causes include low calcium consumption, antacid therapy, and loss from the kidneys or gastrointestinal tract. Chronic magnesium deficiency is associated with hypertension, type 2 diabetes, and metabolic syndrom.

Sources: Magnesium is the 8th most abundant element in the earth's crust. While it is not found free it nature, it is available in minerals including magnesite and dolomite. The metal may be obtained by electrolysis of fused magnesium chloride derived from brines and seawater.

Atomic Weight: 24.305

Element Classification: Alkaline Earth Metal

Isotopes: Magnesium has 21 known isotopes ranging from Mg-20 to Mg-40. Magnesium has 3 stable isotopes: Mg-24, Mg-25 and Mg-26.

Magnesium Physical Data

Density (g/cc): 1.738

Appearance: lightweight, malleable, silvery-white metal

Atomic Radius (pm): 160

Atomic Volume (cc/mol): 14.0

Covalent Radius (pm): 136

Ionic Radius: 66 (+2e)

Specific Heat (@20°C J/g mol): 1.025

Fusion Heat (kJ/mol): 9.20

Evaporation Heat (kJ/mol): 131.8

Debye Temperature (K): 318.00

Pauling Negativity Number: 1.31

First Ionizing Energy (kJ/mol): 737.3

Oxidation States: 2

Lattice Structure: Hexagonal

Lattice Constant (Å): 3.210

Lattice C/A Ratio: 1.624

CAS Registry Number: 7439-95-4

Magnesium Trivia:

  • Magnesium was originally named 'magnium' by Humphrey Davy after isolating the element from magnesia, known now as magnesium oxide.
  • The 1915 Nobel Prize in Chemistry was awarded to Richard Willstätter for his work with the chlorophyll and identifying magnesium was the central atom in its structure.
  • Epsom salt is a magnesium compound, magnesium sulfate (MgSO4).
  • Magnesium is the 10th most abundant element in the human body.
  • Magnesium will burn in pure nitrogen gas and pure carbon dioxide gas.
  • Magnesium is the fifth most common element found in seawater.


  • Emsley, John (2011). Nature's building blocks: An A-Z Guide to the Elements. Oxford University Press. ISBN 978-0-19-960563-7.
  • Greenwood, Norman N.; Earnshaw, Alan (1997). Chemistry of the Elements (2nd ed.). Butterworth-Heinemann. ISBN 978-0-08-037941-8.
  • Hammond, C. R. (2004). The Elements, in Handbook of Chemistry and Physics (81st ed.). CRC press. ISBN 978-0-8493-0485-9.
  • Rumble, John R., ed. (2018). CRC Handbook of Chemistry and Physics (99th ed.). Boca Raton, FL: CRC Press. ISBN 978-1-1385-6163-2.
  • Weast, Robert (1984). CRC, Handbook of Chemistry and Physics. Boca Raton, Florida: Chemical Rubber Company Publishing. ISBN 0-8493-0464-4.

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Your Citation
Helmenstine, Anne Marie, Ph.D. "Magnesium Facts (Mg or Atomic Number 12)." ThoughtCo, Feb. 16, 2021, Helmenstine, Anne Marie, Ph.D. (2021, February 16). Magnesium Facts (Mg or Atomic Number 12). Retrieved from Helmenstine, Anne Marie, Ph.D. "Magnesium Facts (Mg or Atomic Number 12)." ThoughtCo. (accessed June 8, 2023).