What is gallium?
Gallium is a p-block chemical element or soft, silvery metal of group-13 of the periodic table with atomic number 31 and symbol Ga. The use of gallium sharply increases in recent years due to the development of semiconductor technology. Among group-13 elements, the extremely high melting point of boron indicates that it has a very strong binding force. Aluminum is comparatively soft. Gallium is liquid over a wide range of temperatures which is used in high-temperature thermochemistry. It is found mostly in sulfide minerals containing zinc.
Who discovered gallium?
In 1870, Mendeleev made wonderful predictions about gallium and he named it eka-aluminum. In 1875, France chemist Paul-Émile Lecoq de Boisbaudran discovered or isolated the element from crude zinc blende. The name of gallium was given in honor of France (Latin name Gallia). The element is placed in period-4 and group-13 with p-block elements.
Properties of gallium
Gallium is low melting, soft, silvery lustrous metal. The low low melting point of gallium has no simple explanation. It might be explained by the filled d10 configuration. But the boiling point of Ga is not lower than Al. Therefore, it has the longest liquid range for any element. It is not attacked by water owing to the protective oxide coating. Gallium dissolves in aqueous hydrochloric acid by forming Ga+3 ion. It is scarcely attacked by dilute sulfuric acid but concentrated sulfuric acid reduced to SO2. Dilute and concentrated nitric acid formed a protective layer on the metal surface.
|Properties of gallium
|Electronic configuration||[Ar] 3d10 4s2 4p1|
|Melting point||29.76 °C|
|Boiling point||2400 °C|
|Molar heat capacity||25.86 J mol-1K-1|
|Electrical resistivity||270 nΩ·m|
|Common oxidation number||+3|
|Electronegativity||Pauling scale: 1.81|
Where is gallium found?
Gallium is found in earth much less abundant than aluminum. It is found associated with aluminum, coal, and sulfide mineral of zinc and germanium. Previously, it was obtained from the flew dust emitted during the burning of coal or roasting of sulfide ores. Now, gallium is obtained as a by-product in the aluminum industry.
Previously, it was extracted from ashes of coal or electrolysis of gallium salts. At present, gallium is produced as a by-product of aluminum extraction. Ga(OH)3 is a stronger acid than Al(OH)3 due to the greater electric polarization power of Ga+3 ion. Therefore, Sodium gallate (Na3GaO3) solution is obtained during the purification of bauxite by Bayer’s process. The solution containing sodium gallate is electrolysis to obtain the metal. Very pure gallium which is used in semiconductors is made by further chemical treatment followed by zone refining.
Interesting facts about gallium
The middle member gallium of group-13 differs remarkably from the first member of group-13.
- It exhibits greater chemical reactivity at moderate temperatures.
- Gallium has distinct cationic chemistry in aqueous solutions.
- It has no series of volatile hydrides and cluster compounds like boranes and carboranes.
Gallium(III) oxide is the chemical compound of metal having the molecular formula Ga2O3. At high temperatures, it formed α-Ga2O3, and at low temperatures, it formed γ-Ga2O3. It is used as an intermediate for the purification of Ga metal.
Gallium hydride (GaH3) is similar to that of AlH3 but it is thermally less stable. The viscosity of GaH3 is very high which decomposes completely to the free element at room temperature. It may be prepared by reacting lithium gallanate (LiGaH4) with gallium(III) chloride at −30 °C. 3LiGaH4 + GaCl3 → 3 LiCl + 4GaH3. It acts as a lewis acid.
Gallium(III) chloride is a volatile crystal lattice containing dimeric molecules with the molecular formula GaH3. It is prepared by heating metal in atmospheric chlorine or HCl gas. GaH3 forms long white needles which fume in moist air due to the formation of HCl through hydrolysis. The dimeric form of GaH3 is formed below 600°C. Gallium(III) chloride is an efficient chemical catalyst that AlCl3 for some hydrocarbon synthesis processes.
Ga(III) sulfate is the chemical compound of gallium with the molecular formula Ga2(SO4)3, or Ga2(SO4)3, xH2O. The crystalline form like Ga2(SO4)3, 18H2O obtained by dissolving gallium metal in dilute sulfuric acid solution.
Uses of Gallium
- In recent years, the uses of gallium are sharply increased due to the development of semiconductor technology. GaAs is largely used in light-emitting diodes or LED. It can directly convert electricity into coherent light or laser diodes. Such types of LED are familiar in pocket calculators and similar output display devices.
- Gallium metal is also used for making infrared emitting diodes, infrared detectors, and photomultiplier tubes. GaAs1-xPx system now virtually dominated the LED market.
- It is very useful in high-temperature thermometers, barometers, pharmaceuticals, and other nuclear medicine tests.
- It is used in high-temperature liquid seals, low-temperature solders, manometric fluid, and heat transfer media.