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Gallium (Ga)

Gallium (symbol Ga) is the chemical element with atomic number 31: a post-transition metal, solid at 0 °C, with an atomic mass of 69.723 u. Discovered in 1875 (Paul-Émile Lecoq de Boisbaudran).

Gallium is a silvery metal that melts at 29.8 °C: rest it on your palm and it slumps into a shiny puddle. Predicted by Mendeleev before it was even discovered, it has become a pillar of modern electronics. Combined with nitrogen or arsenic, it forms semiconductors that make blue and white LEDs shine and boost the signal in our smartphones.

Key facts

Atomic number
31
Symbol
Ga
French name
Gallium
Atomic mass
69.723 u
Molar mass
69.723 g/mol
Family
Post-transition metals
Position
period 4, group 13, p-block
State at 0 °C
Solid
Melting point
29.8 °C
Boiling point
2,399.9 °C
Density
5.91 g/cm³
Electronegativity (Pauling)
1.81
First ionization energy
579 kJ/mol
Atomic radius
130 pm
Electron configuration
[Ar] 3d¹⁰ 4s² 4p¹
Abundance in Earth's crust
19 ppm (35th most abundant element)
Indicative price
150 $/kg (order of magnitude)
Radioactive
no
Discovery
1875, Paul-Émile Lecoq de Boisbaudran

Origin of the name

From the Latin Gallia, Gaul, meaning France.

What does gallium look like?

A soft, silvery-gray metal that looks like aluminium when solid and like mercury once melted. It forms beautiful crystals and, like water, expands as it freezes.

Where is gallium found?

Gallium makes up about 19 ppm (grams per tonne) of Earth's crust, as much as lead, but it is very scattered: there are virtually no deposits where it is concentrated. It occurs as traces in bauxite (aluminium ore) and in sphalerite (zinc ore).

Natural sources

  • Bauxite (traces)
  • Sphalerite (traces)
  • Gallite (very rare)

How is gallium produced?

It is recovered as a by-product of refining bauxite into alumina (the Bayer process), and more rarely from zinc refining. World output of primary gallium is just a few hundred tonnes a year, about 98% of it in China. In 2023, Beijing put its exports under license, sending prices soaring.

Top producers

  • China
  • Russia
  • Japan
  • South Korea

What is gallium used for?

  • Gallium nitride (GaN) in blue and white LEDs.
  • Compact GaN fast chargers.
  • Gallium arsenide (GaAs) in phone radio amplifiers.
  • High-efficiency solar cells for satellites.
  • Galinstan, a liquid alloy used in mercury-free thermometers.

In everyday life

  • LED bulbs and screens
  • Smartphone (radio-frequency chips)
  • Compact “GaN” USB-C charger
  • Mercury-free medical thermometer

Role in living things

Gallium has no known role in living things. Some of its radioactive isotopes (gallium-67 and gallium-68), however, are used in nuclear medicine to pinpoint tumors or infections on scans.

Hazards of gallium

It is not very toxic on the skin, though it stains it gray. Its main danger is to other metals: liquid gallium seeps between the grains of aluminium and makes it as brittle as a cookie, which is why it is banned from airline luggage.

Cosmic origin

  • Supernovae: Forged in the cores of massive stars, then scattered when they explode.
  • Dying stars: Made slowly in red giants (stars like the Sun at the end of their lives).

History of gallium

In 1871, Mendeleev predicted an “eka-aluminium” with a density of 5.9. In 1875, Frenchman Paul-Émile Lecoq de Boisbaudran discovered it by spotting two unknown violet lines in the spectrum of a zinc ore, and named it after Gaul (Gallia). He first measured a density of 4.7; Mendeleev wrote to tell him he was wrong, and a measurement on a purified sample did indeed give 5.9.

Did you know?

  • A gallium spoon melts when you stir hot tea with it: a classic chemist's magic trick.
  • Lecoq de Boisbaudran was suspected of slipping his own name into gallium (“coq,” rooster, is gallus in Latin); he always denied it.
  • Gallium stays liquid over a huge range: from 29.8 °C up to about 2,400 °C.
  • Blue gallium nitride LEDs earned Akasaki, Amano and Nakamura the 2014 Nobel Prize in Physics.

Isotopes of gallium

Two stable isotopes, gallium-69 and gallium-71. Its radioactive forms, 67 and 68, help pinpoint tumors and infections in medical imaging.

  • gallium-67: radioactive, half-life 3.26 days. Scintigraphy to locate certain tumors and infections.
  • gallium-68: radioactive, half-life 1.13 h. PET imaging of neuroendocrine tumors and prostate cancer.
  • gallium-69: 60.108% of natural gallium, stable
  • gallium-71: 39.892% of natural gallium, stable. Dozens of tonnes of gallium were used to detect neutrinos from the Sun.

Common compounds

Gallium arsenide (GaAs) · Gallium nitride (GaN)

Related elements

Same family (post-transition metals): Aluminium (Al), Indium (In), Tin (Sn), Thallium (Tl), Lead (Pb), Bismuth (Bi), Polonium (Po).

Same column (group 13): Boron (B), Aluminium (Al), Indium (In), Thallium (Tl), Nihonium (Nh).