Gallium is the only metal, except for mercury, caesium, and rubidium, which can be liquid near room temperatures; this makes possible its use in high-temperature thermometers. It has one of the longest liquid ranges of any metal and has a low vapour pressure even at high temperatures.
Ultra-pure gallium has a beautiful, silvery appearance, and the solid metal exhibits a conchoidal fracture similar to glass. The metal expands on solidifying; therefore, it should not be stored in glass or metal containers, as they may break as the metal solidifies.
High-purity gallium is attacked only slowly by mineral acids. Gallium arsenide is capable of converting electricity directly into coherent light and gallium arsenide is a key component of LEDs (light emitting diodes). In the 1990s gallium nitride (GaN) was discovered to emit blue light in light-emitting diodes (LEDs). As red and green LEDs were already known, this meant that red green, and blue LEDS could be used in full-colour LED displays while white LEDs and blue laser devices became possible as well.
Image adapted with permission fromProf James Marshall's (U. North Texas, USA)Walking Tour of the elements CD.
Gallium wasdiscovered by Paul-Emile Lecoq de Boisbaudran in 1875 at France.Origin of name: from the Latin word "Gallia" meaning "France" and perhaps also from the Latin word "gallus", (the cock, a translation of Lecoq, the discoveror of gallium).
Isotope abundances of gallium with the most intense signal set to 100%.
Gallium has two stable isotopes and both are used in nuclear medicine and physics. Ga-69 is used for production of the radioisotope Ge-68. This isotope is used for so-called Ge-68/Ga-68 generators. The Ga-68 that is created from the decay of Ge-68 is used as a PET isotope. Ga-71 has been used to study the behavior of solar neutrinos and it is also used in NMR studies.
Isolation: gallium is normally a byproduct of the manufacture of aluminium. The purification of bauxite by the Bayer process results in concentration of gallium in the alkaline solutions from an aluminium:gallum ratio from 5000 to 300. Electrolysis using a mercury electrode gives a further concentration and further electrolysis using a stainless steel cathode of the resulting sodium gallate affords liquid gallium metal.
Very pure gallium requires a number of further processes ending with zone refining to make very pure gallium metal.
Density of solid: 5904 kg m-3
Molar volume: 11.80 cm3
Thermal conductivity: 29 W m‑1 K‑1
Melting point: 302.91 [29.76 °C (85.57 °F)] K
Boiling point: 2477 [2204 °C (3999 °F)] K
Enthalpy of fusion: 20.5 kJ mol-1
Atomic radius (empirical): 130 pm
Molecular single bond covalent radius: 124 (coordination number 3) ppm
van der Waals radius: 232 ppm
Pauling electronegativity: 1.81 (Pauling units)
Allred Rochow electronegativity: 1.82 (Pauling units)
Mulliken-Jaffe electronegativity: 2.01 (sp2 orbital)
First ionisation energy: 578.84 kJ mol‑1
Second ionisation energy: 1979.41 kJ mol‑1
Third ionisation energy: 2964.58 kJ mol‑1
Universe: 10 ppb by weight
Crustal rocks: 19000 ppb by weight
Human: (no data) ppb by weight
