Gallium
Atomic Data
| Atomic Number | 31 |
| Symbol | Ga |
| Atomic Weight | 69.723 u |
| Density (STP) | 5.91 g/cm³ |
| Melting Point | 29.76 °C (302.91 K) |
| Boiling Point | 2203.85 °C (2477 K) |
| Electronegativity | 1.81 (Pauling) |
| Electron Config. | 1s2 2s2 2p6 3s2 3p6 3d10 4s2 4p1 |
| Oxidation States | +3 |
| Phase at STP | Solid |
| Category | Post-Transition Metal |
| Period / Group | 4 / 13 |
| CAS Number | 7440-55-3 |
Electron Configuration
[Ar] 3d10 4s2 4p1
| Shell | n | Subshell | Electrons | Cumulative |
|---|---|---|---|---|
| K | 1 | 1s | 2 | 2 |
| L | 2 | 2s | 2 | 4 |
| L | 2 | 2p | 6 | 10 |
| M | 3 | 3s | 2 | 12 |
| M | 3 | 3p | 6 | 18 |
| M | 3 | 3d | 10 | 28 |
| N | 4 | 4s | 2 | 30 |
| N | 4 | 4p | 1 | 31 |
| Total | 31 | 31 | ||
Isotopes of Gallium
Gallium has two naturally occurring stable isotopes. The most abundant is ⁶⁹Ga, comprising 60.108% of all naturally occurring Gallium.
| Isotope | Symbol | Protons | Neutrons | Abundance | Stability |
|---|---|---|---|---|---|
| Gallium-69 | ⁶⁹Ga | 31 | 38 | 60.108 | Stable |
| Gallium-71 | ⁷¹Ga | 31 | 40 | 39.892 | Stable |
Abundance & Occurrence
Gallium is present in Earth's crust at approximately 19 ppm by mass and at approximately 1 ppm by mass throughout the universe.
Earth's Crust (ppm by mass)
Universe (ppm by mass)
Discovery & History
Read more about the discovery of the periodic table of elements →
Safety & Handling
- Gallium arsenide (GaAs): toxic: Gallium arsenide, used in semiconductors and LEDs, is classified as a Group 1 human carcinogen (IARC) when in particle form; inhalation of GaAs dust causes lung cancer: handle only under strict engineering controls.
- Skin and eye contact: Molten gallium metal wets and penetrates many surfaces; contact with skin causes mild irritation, but gallium rapidly alloys with aluminium and other metals, weakening structural components.
- Thermal expansion: Gallium expands on solidifying; never seal liquid gallium in a closed container: the expansion on freezing can rupture glassware or rigid containers.
- Gallium compounds: Gallium trichloride and other halide compounds are corrosive and moisture-sensitive; handle in dry, ventilated conditions with appropriate gloves and eye protection.
Gallium in the Real World
Real-World Uses
- Semiconductor devices (LEDs and laser diodes): Gallium nitride (GaN) is the semiconductor material behind blue and white LEDs (which enabled energy-efficient lighting worldwide) and blue laser diodes used in Blu-ray players.
- High-frequency electronics: Gallium arsenide (GaAs) and gallium nitride (GaN) transistors operate efficiently at microwave and millimetre-wave frequencies, used in 4G/5G mobile phone transceivers, radar systems, and satellite communications.
- Photovoltaic cells: Multijunction solar cells based on GaAs, GaInP, and related gallium compounds achieve efficiencies above 40% under concentrated sunlight and are used in space satellites and solar concentrator systems.
- Medical imaging: Gallium-67 citrate is taken up by rapidly dividing cells and accumulates in tumours and sites of infection; it is used in SPECT nuclear medicine imaging to detect lymphoma, osteomyelitis, and inflammatory disease.
- Low-melting alloys and thermometers: Gallium melts at 29.8 °C (just above room temperature) and forms liquid gallium-indium-tin alloys used in non-toxic thermometers and as stretchable electrical conductors for flexible electronics research.
Downloadable Resources
Free periodic table reference sheets for classrooms, study sessions, and laboratory use.
Frequently Asked Questions
What is gallium used for?
Gallium's most important application is in compound semiconductors: gallium arsenide (GaAs) and gallium nitride (GaN) are used in LEDs, laser diodes, solar cells, and high-frequency transistors in mobile phones and radar systems. GaN transistors are increasingly used in fast-charging power adapters. Gallium is also used in some thermometers as a non-toxic alternative to mercury.
Is gallium liquid at room temperature?
Nearly. Gallium has a melting point of just 29.76 °C (85.6 °F), which means it melts in your hand. It is a solid at typical room temperature but becomes liquid on a warm day or when held. Gallium is famously used in the party trick of 'gallium spoons' that melt when stirred into hot water, as its low melting point makes it unnoticeable in solid form.
How was gallium discovered?
Gallium was discovered in 1875 by French chemist Paul Emile Lecoq de Boisbaudran via spectroscopy of a zinc ore. Remarkably, its existence, approximate atomic weight, and properties had been predicted four years earlier by Dmitri Mendeleev, who called it 'eka-aluminium'. Gallium's discovery was one of the greatest early triumphs of the periodic table as a predictive tool.
Why is gallium important for LEDs?
Gallium nitride (GaN) is a wide-bandgap semiconductor that emits blue and ultraviolet light when electrons cross the bandgap. The invention of efficient blue GaN LEDs in the 1990s by Isamu Akasaki, Hiroshi Amano, and Shuji Nakamura completed the RGB set needed for white LEDs and full-colour LED displays, earning the inventors the 2014 Nobel Prize in Physics.