Gallium – facts and properties

Position in the periodic table

View the full periodic table

Occurrence and extraction

Gallium never occurs as a free metal and hardly forms ores of its own. In the Earth's crust it is more common than some well-known metals, but spread extremely thinly. Traces are found in bauxite, the main aluminium ore, and in zinc ores. Because gallium is chemically very similar to aluminium, it follows aluminium through the refining process.

For that reason gallium is made as a by-product. When aluminium oxide is extracted from bauxite, gallium builds up in the sodium hydroxide solution and can be deposited from it by electrolysis. Smaller amounts come from zinc smelting. The metal is then purified to a very high degree for use in semiconductors. China produces most of the world's supply, and the European Union lists gallium as a critical raw material because so few countries supply it.

The element was discovered in 1875 by the French chemist Paul-Émile Lecoq de Boisbaudran. In a sample of zinc blende he saw two violet lines in the spectrum that matched no known element. The name comes from Gallia, the Latin name for France. In 1871 Mendeleev had predicted an element that should sit below aluminium and had called it eka-aluminium. Gallium fitted his prediction for atomic mass, density and compounds. That was strong evidence that the periodic table reveals real regularities and does not merely sort the elements.

Properties and reactions

Gallium is in period 4 and group 13. Its electron configuration is [Ar] 3d¹⁰ 4s² 4p¹, which gives it 3 valence electrons. Its electronegativity is 1.81. The metal has a density of 5.91 g/cm³, melts at 29.76 °C and boils only at 2204 °C. The gap between melting and boiling point is larger than for almost any other metal, so gallium stays liquid over an enormous temperature range.

Gallium shares one oddity with water: it expands as it freezes. Glass or metal containers can burst, so the metal is stored in plastic. Liquid gallium wets glass and skin and leaves grey stains of oxide. It also behaves badly towards aluminium: it creeps between the metal grains and makes aluminium brittle, so gallium should be kept away from aluminium parts.

In compounds gallium almost always carries three positive charges. As with aluminium, the hydroxide is amphoteric and dissolves in both acids and strong alkalis. In air a thin oxide layer forms that protects the metal from further oxidation.

Uses in everyday life and technology

Almost all gallium goes into semiconductor technology. Blue LEDs are based on gallium nitride. The blue LED, honoured with the Nobel Prize in Physics in 2014, made white LED lighting possible, because most white LEDs are a blue diode topped with a phosphor. Gallium nitride is also used in compact fast chargers, since it withstands higher voltages and temperatures than silicon.

Gallium arsenide is a compound semiconductor in which electrons move unusually fast. It is found in radio-frequency parts in mobile phones, in laser diodes and in solar cells. These cells are expensive but efficient and light, which is why they mostly power satellites.

An alloy of gallium, indium and tin, known as galinstan, stays liquid at room temperature and replaces toxic mercury in some thermometers. In medicine the radioactive isotope gallium-68 is used in PET scans to make tumours visible.

The metal itself is considered of low toxicity, but gallium has no known function in the body. Gallium arsenide dust is harmful because of its arsenic content and is handled only in industry.

Molecules containing this element

• Gallane GaH₃View in 3D

Quick question

What is the atomic number of gallium (Ga)?

FAQ