Gallium

Gallium is a soft, silvery metal with one of the most remarkable properties of any element: it melts at just 29.8°C, barely above room temperature, and below the temperature of the human body. A lump of gallium placed on your palm will slowly melt into a shiny liquid puddle. Today it is found in LEDs, semiconductors and next-generation power electronics.

  • Atomic Number3131 protons, 31 electrons
  • Atomic Mass69.723 uAbout 70× heavier than hydrogen
  • State at Room TempSolidsoft, silvery-white metal
  • Density5.91 g/cm³Denser than water but barely
  • Melting / Boiling29.8°C / 2203.8°CMelts at just 29.8°C, body temperature!
  • Discovered1875Paul-Émile Lecoq de Boisbaudran, 1875

Gallium is the first post-transition metal of Period 4. How does it compare?

Gallium bridges the transition metals and the non-metals in Period 4.

Atomic Mass Comparison
Zinc65.4 u
Gallium69.7 u
Germanium72.6 u
Arsenic74.9 u
Iron55.8 u

Gallium (69.7 u) sits just above the mass of iron (55.8 u), opening a new stretch of the periodic table. Beyond gallium, elements become increasingly varied in their properties as we move through post-transition metals and metalloids.

What is gallium?

Gallium is a post-transition metal in Group 13 of the periodic table, sitting below aluminium. It has 31 protons and three electrons in its outer shell. What makes gallium extraordinary is its melting point of just 29.8°C: one of the lowest of any metal, combined with a boiling point of 2,229°C. This gives gallium the widest liquid range of any element by absolute temperature. Liquid gallium also expands slightly on solidifying (like water), making it useful in high-temperature thermometers.

Gallium gets its name from Gallia: the Latin name for France, chosen by its discoverer Paul-Émile Lecoq de Boisbaudran, a French chemist, as a patriotic tribute. Some suspected he also named it for himself, since Lecoq in French means "the rooster" and gallus in Latin means "rooster" too, though Lecoq denied this. Remarkably, gallium's existence was predicted by Mendeleev in 1871, who called the unknown element eka-aluminium. When gallium was discovered in 1875, it matched Mendeleev's predictions extremely closely, further cementing the periodic table's authority.

Fact Gallium is one of very few metals that melts at room temperature or just above. At approx. 30°C it liquefies, meaning you can hold a solid piece of gallium in your gloved hand and watch it melt into a mirror-like liquid puddle. It can then be poured into a mould and will solidify again when cooled. This unusual property makes it a popular demonstration metal in chemistry education.

Where you find gallium

On Earth

Gallium is relatively rare, approx. 19 parts per million in the Earth's crust, but it is never found as a free metal. It is always dispersed in low concentrations in other minerals.

  • By-product of aluminium production. Gallium substitutes for aluminium in bauxite minerals. It is almost entirely recovered as a by-product of processing bauxite into aluminium, extracted from the waste solution (Bayer liquor) in a separate step.
  • By-product of zinc smelting. Gallium also occurs in sphalerite (zinc ore) and is sometimes recovered during zinc processing.
  • China dominates. China produces approx. 80% of the world's gallium, a significant advantage in a world increasingly dependent on gallium for electronics and defence applications.

How we use gallium

  • LEDs and laser diodes. Gallium nitride (GaN) and gallium arsenide (GaAs) semiconductors are the basis of virtually all LED lighting, Blu-ray laser diodes, and the LEDs in traffic lights, smartphone screens and stadium displays.
  • 5G electronics. Gallium nitride transistors handle high frequencies and high power with very low losses, making them ideal for the radio frequency amplifiers in 5G base stations and satellite communications.
  • Solar cells. Gallium arsenide solar cells achieve higher efficiencies than silicon cells and are used in space satellites where maximum power from minimum panel area matters most.
  • Power electronics. GaN power converters are rapidly replacing silicon in fast phone chargers, electric vehicle chargers and data centre power supplies.
Did you know? Mendeleev predicted the existence of gallium in 1871, four years before it was actually discovered. He called it eka-aluminium and predicted its atomic mass, density, melting point and the compounds it would form. When gallium was found in 1875, it was so close to his predictions that it convinced even the most sceptical chemists that the periodic table was a genuine scientific law capable of predicting the unknown.

How it was discovered

Gallium was discovered in 1875 by the French chemist Paul-Émile Lecoq de Boisbaudran using spectroscopy: the technique of identifying elements by the unique wavelengths of light they emit. He was analysing a zinc ore from the Pyrenees and spotted two previously unknown spectral lines. He extracted the new element by electrolysis of its solution, producing a tiny amount of pure gallium. The match between the new element and Mendeleev's eka-aluminium prediction was striking, making gallium one of the most famous confirmations of a scientific prediction in history.

Deeper dive: gallium nitride and the LED revolution

Gallium nitride (GaN) is one of the most important semiconductor materials of the 21st century. The 2014 Nobel Prize in Physics was awarded to Isamu Akasaki, Hiroshi Amano and Shuji Nakamura for inventing the blue GaN LED in the early 1990s. This was a landmark achievement: red and green LEDs existed, but without blue, no white LEDs (which mix red, green and blue) or Blu-ray lasers were possible. The blue LED enabled LED lighting that now illuminates homes worldwide, consuming approx. 90% less energy than incandescent bulbs.

GaN power electronics are driving a revolution in energy conversion. Traditional silicon transistors lose significant energy as heat when switching at high frequencies. GaN can switch much faster and at higher voltages with far less loss. The fast chargers that can fill a phone battery in 20 minutes use GaN transistors. Data centres, which consume enormous amounts of electricity, are switching to GaN power supplies to reduce their energy use.

Gallium arsenide (GaAs) was the dominant compound semiconductor before GaN and is still used in solar cells aboard satellites. GaAs cells achieve approx. 30% efficiency (compared to around 22% for the best silicon cells) because GaAs absorbs sunlight more efficiently across the solar spectrum. Triple-junction GaAs cells, which stack three different GaAs compositions to capture different parts of the spectrum, can exceed 40% efficiency under concentrated sunlight.

Gallium is a metal that bridges the ordinary and the extraordinary, melting in your hand yet enabling the LED lights and 5G networks of the modern world. Moving to 32 protons brings us to germanium, another element predicted by Mendeleev and vital for modern electronics.