Gallium
Element 31 · Post-Transition Metal
Gallium is a soft, silvery post-transition metal famous for a party trick: it melts at just 29.76 °C, so it liquefies in a warm hand. Unusually, it expands when it freezes, like water. It also wets glass, leaving a silvery mirror-like stain on contact.
Gallium's real importance is electronic. Gallium arsenide and gallium nitride are the semiconductors behind blue LEDs, laser pointers, phone fast-chargers, and 5G equipment — materials that do jobs silicon cannot. It is non-toxic in small amounts but handled carefully in labs.
Key facts
| Atomic number | 31 |
|---|---|
| Atomic weight | 69.723 |
| Category | Post-Transition Metal |
| Group / Period | 13 / 4 |
| Block | p |
| Electron configuration | [Ar] 3d10 4s2 4p1 |
| Common oxidation states | +3 |
| State at STP | Solid |
| Electronegativity | 1.81 |
| Atomic radius | 136 pm |
| Density | 5.91 g/cm³ |
| Melting point | 29.76 °C |
| Boiling point | 2204 °C |
Occurrence
Gallium never occurs free and is found only in traces, mainly in bauxite (aluminium ore) and zinc ores, from which it is recovered as a byproduct. Mendeleev predicted it as eka-aluminium in 1871, and its discovery in 1875 was a triumph for the periodic table.
Applications
Gallium arsenide and gallium nitride make LEDs and laser diodes
Smartphone chargers and 5G base stations use gallium nitride power chips
High-temperature thermometers use gallium instead of toxic mercury
Semiconductor wafers for optoelectronics are grown from gallium compounds
Low-melting gallium alloys serve in specialized solders and mirrors
Common compounds
- gallium arsenide
- gallium nitride
- gallium oxide
- gallium chloride
Gallium melts at 29.76 °C — a solid spoon of it would melt in a cup of hot tea.
Data source: IUPAC standard atomic weights 2021