|Name: gallium||Group number: 13|
|Symbol: Ga||Group name: (none)|
|Atomic number: 31||Period number: 4|
|Atomic weight: 69.723 (1)||Block: p-block|
|CAS Registry ID: 7440-55-3||Voice: |
|Standard state: solid at 298 K (but melts only slightly||Colour: silvery white|
|Classification: Metallic||Availability: |
Image adapted with permission from Prof James Marshall"s (U. North Texas, USA) Walking Tour of the elements CD.
It 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).
IsolationHere is a brief summary of the isolation of gallium.
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.