Gallium (Ga)

Gallium melts at 29.76 °C, so a lump held in a warm hand turns into a silvery puddle in a minute or two — the classic chemistry-department party trick, along with the gallium spoon that dissolves in a cup of tea. It has the largest liquid range of any element in ordinary use, staying molten from 30 °C to over 2,200 °C. Blue LEDs, and therefore all white LED lighting, are gallium nitride; the material took thirty years to make work and earned the 2014 Nobel Prize in Physics.

Properties

Atomic number

31

Symbol

Ga

Standard atomic weight

69.723 u

Category

Post-transition metal

Group

13

Period

4

Block

p-block

Electron configuration

[Ar] 4s² 3d¹⁰ 4p¹

Electrons per shell

2, 8, 18, 3

Melting point

302.91 K — 29.8 °C — 85.6 °F

Boiling point

2,477 K — 2203.8 °C — 3998.9 °F

Density

5.91 g/cm³

Electronegativity

1.81 (Pauling)

Oxidation states

+3

Discovered

1875 by Paul-Émile Lecoq de Boisbaudran

Electron configuration

Full

1s² 2s² 2p⁶ 3s² 3p⁶ 4s² 3d¹⁰ 4p¹

Noble gas shorthand

[Ar] 4s² 3d¹⁰ 4p¹

Shells

K: 2 · L: 8 · M: 18 · N: 3

What it is used for

• Gallium nitride in blue and white LEDs and fast phone chargers
• Gallium arsenide in phone radio front-ends and satellite solar cells
• Radar and 5G power amplifiers
• Gallium-67 and gallium-68 tracers in nuclear medicine
• Low-melting alloys, including galinstan thermometer fluid

Hazards

• Wets and embrittles aluminium badly, so it must be kept away from aircraft and aluminium tooling

Mendeleev predicted it as eka-aluminium in 1871 and got the density wrong; when Lecoq de Boisbaudran measured 4.7 g/cm³, Mendeleev wrote to say the sample must be impure. He was right — the true value is 5.91.

Neighbours in the table

Group 13

Elements in the same group share their outer electron count, which is why they behave similarly in reactions. Gallium sits in group 13 with boron, aluminum, indium, thallium, nihonium.