The silvery metallic element gallium (symbol Ga) is almost a liquid at room temperature. With a melting point of 29.78 °C (302.93 K, 85.604004 °F) and a boiling point: 2403.0 °C (2676.15 K, 4357.4 °F) it has one of the largest liquid ranges of all the elements. It is a p-block element with atomic number 31 occurring in period 4 and group 13 of the periodic table. The element has an ionization energy of 5.999 eV and an oxidation state of +3. Gallium’s atomic weight is 69.723 and its density 5.91 grams per cubic centimeter.
When Mendeleev first designed his periodic table in 1871, no element with an atomic number of 31 was known. However, he knew one should exist and assigned a space in the table to an element he called “eka-aluminium”. He also suggested some probable properties of the then unknown element. When Paul-Emile Lecoq de Boisbaudran discovered gallium in 1875, Mendeleev’s predictions proved correct.
When liquefied gallium tends to super-cool and remains in the liquid form at temperatures below its freezing point. To solidify super-cooled liquid gallium small amount of the solid metal are added in a process known as “seeding”. As liquid gallium solidifies, it expands by 3.1 %. When it has solidified, gallium breaks with a conchoidal fracture similar to that seen in glass.
While not found in a pure state in nature trace amounts of gallium occur in the minerals diaspore, sphalerite, germanite and bauxite as well as coal. Its presence in coal leads to some flue dusts from coal burning power stations containing up to 1.5 % gallium. The main source of gallium is bauxite, as it is a by-product from the recovery of aluminum from that mineral. The estimated crustal abundance of gallium is 19 milligrams per kilogram consisting of two stable isotopes, gallium-69 and gallium-71.
Gallium will alloy with most other metals and gallium alloys have low melting points. The pure metal reacts weakly with mineral acids.
The compound gallium arsenide (GaAs) will produce coherent (laser) light directly from electricity. This property has led to its usage in the production of light emitting diodes (LEDs). Solar panels also utilize gallium arsenide. NASA uses gallium arsenide solar panels to power satellites such as the U.S. Naval Academy satellite MidSTAR-1. Gallium nitride (GaN) produces a blue light in LED technology.
Gallium is non-toxic but it has no biological uses.
Los Alamos National Laboratory Chemistry Division
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