Gallium

Gallium is perhaps best known as a metal that is a solid when you pick it up and melts when it sits in your hand. Elemental gallium is a liquid at temperatures higher than 29.76°C, which is below our normal body temperature of 37°C. When you pour liquid gallium from your hand onto a surface at room temperature, it becomes solid again. Even in its solid form, gallium is such a soft metal that you can cut it with a knife.

Gallium has other unusual characteristics. Similar to water, the liquid form expands when it changes state to become a solid. Care must be taken not to store gallium in glass or metal containers as they might rupture.

As far as we know, gallium does not have any natural roles in living things. It is found in humans, but in incredibly small amounts. A person weighing 70 kg would have less than 1 milligram in their body. This likely comes from environmental exposure. Pure elemental gallium is not harmful when touched, but it should not be consumed. An old trick is to stir a hot drink with a spoon made from gallium – the spoon disappears before your eyes – but make sure you do not drink it!

Element facts

Gallium’s official symbol is Ga, from the Latin word ‘Gallia’, meaning Gaul or France – it was discovered by a French chemist. Its atomic number is 31, which means that a gallium atom has 31 protons in its nucleus. Gallium is never found in its elemental form. It is produced as a byproduct of aluminium and zinc production.

Mendeleev’s predictions

When Russian Dmitri Mendeleev produced the periodic table, he grouped elements with similar properties under each other. He left gaps for elements yet to be discovered. Mendeleev predicted the existence of gallium in 1871, which he called eka-aluminium because this undiscovered element would sit under aluminium in the periodic table. Mendeleev also predicted several of the element’s properties and that it would be discovered through spectroscopy (using the properties of light). Paul Émile François Lecoq de Boisbaudran did indeed use spectroscopy to discover gallium. While examining zinc ore in 1875, he saw previously unknown bands of violet-coloured wavelengths and worked to isolate the metal. By 1878, Lecoq de Boisbaudran had purified 75 grams of gallium from 4 tonnes of zinc ore. He was likely the first person to discover that it liquefies when held in one’s hand.

That wasn’t Lecoq de Boisbaudran’s only surprise after discovering gallium, though. Mendeleev published his table in 1869, and gallium was the first new element to be discovered after its publication. Mendeleev tried to claim credit for the discovery, based on his prediction of eka-aluminium. He even went so far as to tell Lecoq de Boisbaudran that his measurements were incorrect as they did not match Mendeleev’s predictions. It turns out that Mendeleev was correct. The Frenchman rescinded his data and published results that confirmed Mendeleev’s predictions.

[Mendeleev] was lucky, really, that a good scientist like Lecoq de Boisbaudran discovered eka-aluminium first. If someone had poked around for one of his mistakes – Mendeleev predicted there were many elements before hydrogen and swore the Sun’s halo contained a unique element called coronium – the Russian might have died in obscurity. ... people tend to remember only Mendeleev’s triumphs.

Sam Keene, The Disappearing Spoon

A useful element

Aside from creating terse debates in scientific journals in the late 1800s, gallium didn’t have a lot of uses. The real breakthrough came a century later with the compound gallium arsenide, which converts electrical current directly into light. Gallium arsenide is used in light-emitting diodes (LEDs), lasers, transistors and photovoltaic cells.