Gallium
Gallium is a chemical element with symbol Ga and atomic number 31. Elemental gallium does not occur in free form in nature, but as the gallium(III) compounds that are in trace amounts in zinc ores and in bauxite. Gallium is a soft, silvery metal, and elemental gallium is a brittle solid at low temperatures, and melts at 29.76 °C (85.57 °F) (slightly above room temperature).
At a glance
- Atomic number
- 31
- Atomic mass
- 69.7231 u
- Phase
- Solid
- Density
- 5.91 g/cm³
- Melting point
- 302.9146 K
- Boiling point
- 2,673 K
- First ionization energy
- 578.8 kJ/mol
- Electronegativity
- 1.81
- Electron affinity
- 41 kJ/mol
- Molar heat capacity
- 25.86 J/(mol·K)
- Period
- 4
- Appearance
- silver-white
Conditions and isotopes affect measured properties. Some properties of short-lived elements are predicted. Electronegativity uses the Pauling scale.
Gallium’s orbitals use a hydrogen-like approximation. Every orbital of each visible subshell is shown: in Shapes as the surface holding half its probability, with light and dark shades for opposite signs of the wavefunction; in Cloud as dots where its electrons are likely to be. Sizes are stepped by shell, like the Shell model.
18 is the [Ar] core total across three shells.
Preparing the orbital view…
31 protons38 neutrons
Gallium-69: its most common form in nature, or its longest-lived if it has none. The nucleus is drawn far too big: it’s about 100,000 times smaller than the atom.
Turn up the heat
A step of 1 K is the same size as 1 °C, so the two scales are always 273.15 apart. Fahrenheit is different: its degrees are smaller and it starts elsewhere, so water freezes at 273.15 K, 0 °C and 32 °F.25 °C · 77 °FSolid
At this temperature, gallium is a solid.
At normal atmospheric pressure (1 atm). The temperature scale is logarithmic. The particle box is schematic: real samples hold vastly more atoms, and spacing and speeds are not to scale.
Pull the electrons off
GaNeutral atom · no charge
A neutral gallium atom. Removing its first electron takes 579 kJ/mol.
Gallium’s outer shell holds 3 electrons. Even inside it there’s a jump: electron 2 takes 3.4× as much as electron 1, because it sits in a lower-energy subshell. Electron 4 is the first from an inner shell: it sits closer to the nucleus with less shielding, so removing it takes 2.1× as much energy as the one before. Each dashed line on the chart marks another jump, into a shell even closer to the nucleus.
What does this tell us?
- The jumps let you count electrons. Between the dashed lines there are 3, then 18, then 8, then 2 bars. Read backwards, that’s 2, 8, 18, 3: the same electrons per shell as the shell model above. Jumps like these are part of the evidence that shells exist.
- The 3 electrons before the first big jump are gallium’s valence electrons, the ones it uses in chemical reactions. That’s why gallium sits in group 13: every element in the group has the same number of outer electrons, so they react in similar ways.
- Within a shell the steps rise gently. Each electron removed leaves fewer electrons pushing the others away, while the nucleus pulls just as hard, so the next one is held a little more tightly.
- The jump inside the outer shell is evidence that shells are split into subshells (s, p, d and f), each with its own energy. You can explore their shapes in the Orbitals view above.
Show the values as a table
| Electron | Shell | Energy (kJ/mol) | × previous | Value |
|---|---|---|---|---|
| 1 | 4 | 579 | – | Measured |
| 2 | 4 | 1,979 | 3.4 | Measured |
| 3 | 4 | 2,965 | 1.5 | Measured |
| 4 | 3 | 6,102 | 2.1 | Measured |
| 5 | 3 | 8,299 | 1.4 | Estimated |
| 6 | 3 | 10,874 | 1.3 | Calculated |
| 7 | 3 | 13,585 | 1.2 | Calculated |
| 8 | 3 | 16,393 | 1.2 | Calculated |
| 9 | 3 | 20,358 | 1.2 | Calculated |
| 10 | 3 | 23,542 | 1.2 | Calculated |
| 11 | 3 | 27,016 | 1.1 | Calculated |
| 12 | 3 | 30,779 | 1.1 | Calculated |
| 13 | 3 | 34,349 | 1.1 | Calculated |
| 14 | 3 | 45,464 | 1.3 | Estimated |
| 15 | 3 | 49,092 | 1.1 | Estimated |
| 16 | 3 | 52,903 | 1.1 | Estimated |
| 17 | 3 | 57,872 | 1.1 | Estimated |
| 18 | 3 | 61,751 | 1.1 | Estimated |
| 19 | 3 | 65,321 | 1.1 | Estimated |
| 20 | 3 | 73,879 | 1.1 | Estimated |
| 21 | 3 | 77,893 | 1.1 | Estimated |
| 22 | 2 | 193,936 | 2.5 | Estimated |
| 23 | 2 | 205,417 | 1.1 | Estimated |
| 24 | 2 | 217,864 | 1.1 | Estimated |
| 25 | 2 | 230,696 | 1.1 | Estimated |
| 26 | 2 | 245,449 | 1.1 | Estimated |
| 27 | 2 | 258,870 | 1.1 | Estimated |
| 28 | 2 | 276,720 | 1.1 | Estimated |
| 29 | 2 | 287,953 | 1 | Calculated |
| 30 | 1 | 1,225,032 | 4.3 | Calculated |
| 31 | 1 | 1,277,418 | 1 | Calculated |
Successive ionization energies of gas-phase atoms and ions from the NIST Atomic Spectra Database. Solid bars are measured; hatched bars were estimated from nearby measurements or calculated from quantum theory, as is usual for highly charged ions. Electrons are taken from the outermost shell first, a simplification: electrons in different subshells of the same shell also differ in energy. On the log scale each gridline is 10 times the one below.
The metal that melts in your hand
Gallium is a silvery metal, solid at room temperature. But it melts at just 29.8 °C, below the temperature of your body, so a lump held in your palm slowly turns into a shiny liquid, like mercury.
20 °C293 K
Solid spoon
- Melts at
- 29.8 °C Your body is 37 °C
- Boils at
- 2,400 °C It stays liquid over a huge range
- Safe to hold?
- Mostly: unlike mercury it isn’t very toxic, but it stains skin grey
Below 29.8 °C it’s a hard, silvery metal. Warm it past its melting point to see it slump.
It grows when it freezes
Almost everything shrinks when it freezes. Gallium, like water, does the opposite: solid gallium takes up more room than the liquid, so it floats. That’s why gallium is kept in plastic bottles, not glass: as it freezes it can crack the glass.
Drop a frozen lump of each into its own liquid:
Solid gallium floats, only just
Solid gallium takes up 3.2% more room than liquid gallium, so it’s less dense and floats, but only just: 96.9% of it sits below the surface. Water does the same, only more so.
The dashed square shows the room the same amount takes up as a liquid. Size differences are drawn 4 times larger so you can see them.
Gallium in history and today
- Predicted before it was found
In 1871 Mendeleev left a gap in his table below aluminium and predicted the missing element’s properties. Gallium was found in 1875. Its discoverer first measured its density as 4.7; Mendeleev said it should be 5.9, and a careful remeasurement agreed.
- The disappearing spoon
A classic prank: hand someone a gallium teaspoon with their hot tea. As they stir, the spoon melts away into the cup. (Don’t drink the tea.)
- In your pocket
Gallium nitride makes the blue and white LEDs in screens and bulbs, and the small, fast phone chargers that don’t get hot. Gallium arsenide is in the radio chips of mobile phones.
Melting speed is illustrative: a real spoon takes minutes, not seconds, to melt in your hand. Densities from the CRC Handbook, for each solid near its melting point and each liquid at its melting point.
How does it compare?
Density
5.91 g/cm³39th lowest of 99
Melting point
303 K15th lowest of 96
Boiling point
2,673 K47th lowest of 97
Electronegativity
1.8143rd highest of 96
First ionization energy
579 kJ/mol26th lowest of 99
Elements 1–99 from the reference data; heavier elements are left out because only a few atoms have ever been made, so their bulk properties are predictions. First ionization energies come from NIST. Density uses a logarithmic scale, because gases are around a thousand times less dense than solids; gas densities are at 0 °C and 1 atm. Melting and boiling points are at normal pressure. Everyday temperatures and light sources in the pictures are approximate. Hover over a dot to see the element, or click it to compare.
Keep exploring
Explore the stories, imagery, and reference data in more depth. Properties with no value in the reference are marked unavailable.
- GalliumRoyal Society of Chemistry
- GalliumWikipedia
- Quantum numbers and electron configurationsPurdue
- Hydrogenic wavefunctionsNIST
- Ionization energiesNIST Atomic Spectra Database