Atomic number 31
Atomic mass 69.72 g.mol -1
Density 5.1 g.cm-3 at 20°C
Melting point 9.8 °C
Boiling point 2204 °C
Solid gallium is a blue-gray metal with orthorhombic crystalline structure; very pure gallium has a stunning silvery color. Gallium is solid at normal room temperatures, but as well as mercury, cesium, and rubidium it becomes liquid when heated slightly. Solid gallium is soft enough to be cut with a knife. It is stable in air and water; but it reacts with and dissolves in acids and alkalis.
Liquid gallium wets porcelain and glass surfaces; it forms a bright, highly reflective surface when coated on glass. It can be used to create brilliant mirrors. Gallium easily alloys with most metals, so it is used to form low-melting alloys. The plutonium pits of nuclear weapons employ an alloy with gallium to stabilize the allotropes of plutonium.
Analog integrated circuits are the most common application for gallium, with optoelectronic devices (mostly laser diodes and light-emitting diodes) as the second largest end use. Gallium has semiconductor properties, especially as gallium arsendite (GaAs). This can convert electricity to light and is used in light emitting diodes (LEDs) for electronic display and watches.
Gallium is used in some high temperature thermometers.
Gallium does not exist in pure form in nature, and gallium compounds are not a primary source of extraction. Gallium is more abundant than lead but much less accessible bacause it has not been selectively concentrated into minerals by any geological process, so it tends to be widely dispersed. Several ores, such as the aluminum ore bauxite, contain small amount of gallium, and coal may have a relatively high gallium content
One controversy with gallium involves nuclear weapons and pollution. Gallium is used to hold some nuclear bomb pits together. However, when the pits are cut and plutonium oxide powder is formed, the gallium remains in the plutonium. The plutonium then becomes unusable in fuel because the gallium is corrosive to several other elements. If the gallium is removed, however, the plutonium becomes useful again. The problem is that the process to remove the gallium contributes to a huge amount of pollution of water with radioactive substances. Gallium is an ideal element to use in the bomb pits, but pollution is destructive to the earth and to the health of its inhabitants. Even if efforts were taken to remove the pollution from the water, it would significantly increase the costs of the procedure of turning plutonium into a fuel by about 200 million dollars. Scientists are working on another method to clean the plutonium, but it could take years to be completed.