Periodic Table


Atomic number: 12
Atomic weight: 24.3050
Symbol: Mg
Group number: 2
Electronic configuration: [Ne].3s2


Magnesium is the eighth most abundant element in the earth's crust although not found in it's elemental form. It is a Group 2 element (Group IIA in older labelling schemes). Group 2 elements are called alkaline earth metals.

Magnesium is a grayish-white, fairly tough metal. It tarnishes slightly in air, and finely divided magnesium readily ignites upon heating in air and burns with a dazzling white flame. Normally magnesium is coated with a layer of oxide, MgO, that protects magnesium from air and water.

Magnesium is an important element for plant and animal life. Chlorophylls are porphyrins based upon magnesium. The adult human daily requirement of magnesium is about 0.3 g day-1.

General information

Discoveror: Sir Humphrey Davy
Date discovered: 1755
Discovered at: England
Meaning of name: From the Greek word "Magnesia", a district of Thessaly

Physical data

Standard state: solid at 298 K
Colour: silvery white
Density of solid at ambient temperature/kg m-3: 1738
Molar volume/cm3: 14.00

Radii /pm

Atomic: 145
Covalent (single bond):
Pauling radius for the ion [Mg]-: no data

Valence shell orbital radius maxima (Rmax)
orbital s p d f
radius136.9no datano datano data


Both values are quoted on the Pauling scale.

Pauling: 1.31
Allred Rochow: 1.23

Crystal Structure

structure: hcp (hexagonal close-packed)

The following CrystalMaker image represents the solid state structure. For most elements, the most stable allotrope is illustrated. Try WebElements version 2 for interactive virtual reality and CHIME images.


Temperatures (/K)

melting point: 923
boiling point: 1363

Enthalpies /kJ mol-1

fusion: 8.48
vaporization: 128

single bond enthalpies:
Mg-F Mg-Cl Mg-Br Mg-I Mg-Mg
513 406 339 264 8.552

Ionization enthalpies /kJ mol-1

Number Enthalpy


This section gives some data for naturally occurring isotopes.
Nominal mass Accurate mass % natural abundance
24Mg23.9850423 (8)78.99 (3)
25Mg24.9858374 (8)10.00 (1)
26Mg25.9825937 (8)11.01 (2)

Further Information

Copyright 1997 Mark Winter
Department of Chemistry at the University of Sheffield, Sheffield S3 7HF, England.

The current version of this document is at http://www.shef.ac.uk/~chem/web-elements-I/Mg.html