Magnesium Facts

Magnesium Chemical & Physical Properties

Photograph of the element magnesium, with a penny to indicate size of the sample.
Photograph of the element magnesium, with a penny to indicate size of the sample. U.S. Geological Survey

Magnesium Basic Facts

Symbol: Mg

Atomic Weight: 24.305

Discovery: Recognized as an element by Black 1775; Isolated by Sir Humphrey Davy 1808 (England)

Word Origin: Magnesia, a district in Thessaly, Greece

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.

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

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.

References: Los Alamos National Laboratory (2001), Crescent Chemical Company (2001), Lange's Handbook of Chemistry (1952), CRC Handbook of Chemistry & Physics (18th Ed.) International Atomic Energy Agency ENSDF database (Oct 2010)

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