ChemSphere
12Mg24.305

Magnesium

Alkaline earth metal · Period 3 · Group 2 · s-block

Blinding white fire and the green heart of chlorophyll

Atomic mass
24.305 u
State at 25 °C
Solid
Electronegativity
1.31
Melting point
649.9 °C
Boiling point
1,089.9 °C
Configuration
[Ne] 3s2
Building atom…
12 protons 12 neutrons 12 electrons

Magnesium, explained

Overview

Magnesium ([Ne]3s2) gives up its two valence electrons to form Mg2+, a small, doubly charged ion that binds strongly to anions. That is why magnesium oxide has an extremely high lattice energy and melts at 2852 °C, making it useful for furnace linings. The metal is reactive, but a thin oxide film protects it at room temperature. Once ignited, it burns with a blinding white flame rich in ultraviolet light, and it burns so hot that it strips oxygen from water and carbon dioxide, so neither can put it out.

With a density of 1.74 g/cm3, magnesium is the lightest structural metal, about two-thirds the weight of aluminium, and its alloys are used in car parts, laptop cases and aircraft. It is the eighth most abundant element in the crust, and seawater contains about 1.3 grams per litre. Most of the world's magnesium is produced in China by the Pidgeon process, which reduces calcined dolomite with ferrosilicon. In living things, a magnesium ion sits at the centre of every chlorophyll molecule, and Mg2+ is needed by hundreds of enzymes, including all that use ATP.

Discovery

Joseph Black in Edinburgh distinguished magnesia (magnesium oxide) from lime in 1755. In 1808 Humphry Davy obtained an impure magnesium amalgam by electrolysing moist magnesia with mercuric oxide, and in 1831 Antoine Bussy made the metal in coherent form by reducing magnesium chloride with potassium. The name comes from Magnesia, a district of Thessaly in Greece, where magnesium-rich minerals were found.

Where it’s found
Magnesium is obtained from seawater and brines or from the minerals dolomite and magnesite, with most metal produced in China.
What it’s used for
  • Lightweight alloys
  • Flares and fireworks
  • Steel desulfurization
  • Antacids and laxatives
  • Titanium production
  • Refractory furnace linings
In living things
Magnesium is essential: it is the central atom of chlorophyll, and Mg2+ is a cofactor for more than 300 enzymes, stabilizing ATP and DNA. An adult body contains about 25 grams, mostly in bone.
Safety
Solid magnesium is safe to handle, but powder, shavings and ribbon are highly flammable. Burning magnesium reacts with water to release hydrogen, so fires require a Class D extinguisher or dry sand, and its intense light can damage eyes.

How it compares

Where Magnesium sits among all 118 elements on the trends that shape the table.

  • Electronegativity1.31Pauling

    #61 of 100 elements with data

  • Ionization energy738kJ/mol

    #41 of 104 elements with data

  • Atomic radius150pm

    #44 of 95 elements with data

  • Electron affinity-40kJ/mol

    #94 of 109 elements with data

  • Density1.74g/cm³

    #98 of 114 elements with data

  • Melting point923K

    #67 of 110 elements with data

Density
1.74 g/cm³
Atomic radius
150 pm
Covalent radius
139 pm
Molar heat
24.869 J/(mol·K)
Appearance
shiny grey solid
Discovered by
Joseph Black

Inside the atom

12 electrons arranged in 3 shells: 2 · 8 · 2.

Orbital diagram

1s2 2s2 2p6 3s2 · shorthand [Ne] 3s2

  1. 1s2
  2. 2s2
  3. 2p6
  4. 3s2

Each box is an orbital holding up to two electrons of opposite spin. Highlighted subshells hold the valence electrons that decide how Magnesium bonds.

Ionization energies

Energy to remove each electron in turn, on a log scale. The biggest leap, from electron 2 to 3 (×5.3), is where the next electron has to come from a filled shell much closer to the nucleus.

Signature reactions

The chemistry Magnesium is known for.

  1. Redox · Combustion

    Burning magnesium

    Magnesium ribbon burns with a dazzling white light and leaves a white powder of magnesium oxide. The flame reaches about 3100 °C. This reaction is used in flares, sparklers and, historically, photographic flash.

    2Mg(s)+O2(g)2MgO(s)

    Conditions: ignition in air

  2. Redox · Single displacement

    Magnesium burning in carbon dioxide

    Magnesium binds oxygen so strongly that it continues burning in carbon dioxide, leaving white magnesium oxide speckled with black carbon. The demonstration shows why CO2 extinguishers are useless on metal fires. It also illustrates the relative stabilities of MgO and CO2.

    2Mg(s)+CO2(g)2MgO(s)+C(s)

    Conditions: burning magnesium placed in CO2

  3. Acid-base · Neutralization

    Milk of magnesia neutralizing stomach acid

    Magnesium hydroxide, a weak base, neutralizes excess hydrochloric acid in the stomach, relieving heartburn. Because it is only slightly soluble, it acts gently without making the stomach strongly alkaline. The magnesium ions formed also draw water into the intestine, which is why larger doses act as a laxative.

    Mg(OH)2(s)+2HCl(aq)MgCl2(aq)+2H2O(l)

    Conditions: body temperature, stomach

Watch Magnesium react in 3D

Where you’ll meet it

Research

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