- Key People:
- Paul-Ćmile Lecoq de Boisbaudran
- Related Topics:
- chemical element
- boron group element
gallium
Who discovered gallium?
What is galliumās melting point?
How is gallium extracted?
What is galliumās oxidation state in most compounds?
News •
gallium (Ga), chemical element, metal of main Group 13 (IIIa, or boron group) of the periodic table. It liquefies just above room temperature.
| atomic number | 31 |
|---|---|
| atomic weight | 69.723 |
| melting point | 29.76 Ā°C (85.57 Ā°F) |
| boiling point | 2,403 Ā°C (4,357 Ā°F) |
| specific gravity | 5.904 (at 29.6 Ā°C [85.3 Ā°F]) |
| oxidation state | +3 |
| electron config. | [Ar]3d104s24p1 |
History and occurrence
Discovery and prediction
Gallium was discovered in 1875 by French chemist Paul-Ćmile Lecoq de Boisbaudran, who observed its principal spectral lines (distinct lines seen in a spectrum, produced when atoms emit or absorb light at specific wavelengths) while examining material separated from zinc blende. Soon afterward he isolated the metal and studied its properties, which coincided with those that Russian chemist Dmitry Ivanovich Mendeleyev had predicted a few years earlier for eka-aluminum, the then undiscovered element lying between aluminum and indium in his periodic table.
Occurrence and extraction
Though widely distributed at Earthās surface, gallium does not occur free or concentrated in independent minerals, except for gallite (CuGaS2), which is rare and economically insignificant. Gallium is extracted as a by-product from zinc blende, iron pyrites, bauxite, and germanite.
" height="20" alt="HEW Logo">
Properties
Physical properties
Gallium is silvery white and soft enough to be cut with a knife. Unusual for its low melting point (about 29.76 Ā°C [85.57 Ā°F]), gallium expands upon solidification and supercools readily, remaining a liquid at temperatures as low as 0 Ā°C (32 Ā°F).
Gallium remains in the liquid phase over a temperature range of about 2,000 Ā°C (about 3,600 Ā°F), with a very low vapor pressure up to about 1,500 Ā°C (about 2,700 Ā°F)āthe longest useful liquid range of any element. The liquid metal clings to (wets) glass and similar surfaces. The crystal structure of gallium is orthorhombic.
Natural gallium consists of a mixture of two stable isotopesāatoms of the same element that differ in massāgallium-69 (60.4 percent) and gallium-71 (39.6 percent). Gallium has been considered as a possible heat-exchange medium in nuclear reactors, although its high neutron-capture cross sectionāmeaning that it readily absorbs neutronsālimits such use.
Chemical properties
The metal gallium is stable in dry air. Somewhat similar to aluminum chemically, gallium slowly oxidizes in moist air until a protective film forms. Upon burning in air or oxygen, it forms the white oxide Ga2O3.
The trusted destination for professionals, college students, and lifelong learners.
SUBSCRIBE
This oxide can be reduced to the metal when heated at high temperatures in hydrogen, and, with gallium metal at 700 Ā°C (1,300 Ā°F), it gives the lower oxide Ga2O. Gallium does not dissolve in cold nitric acid, because a protective film of gallium oxide forms.
Gallium does not react with water at temperatures up to 100 Ā°C (212 Ā°F) but reacts slowly with hydrochloric and other mineral acids to give the gallium ion Ga3+. The metal dissolves in other acids to give gallium salts, and it dissolves in alkalies, with the evolution of hydrogen, to give gallates, such as [Ga(OH)4]ā, in which gallium appears in the anion.
Gallium is amphoteric, meaning that it can react either as an acid or as a base, depending on the conditions. It reacts with sodium and potassium hydroxide solutions to yield a gallate and hydrogen gas. The halogens attack it vigorously.
Oxidation states and compounds
An oxidation state is a number used in chemistry to show how many electrons an atom effectively loses or gains when it forms a compound.
For example, in gallium oxide (Ga2O3), each gallium atom has an oxidation state of +3, meaning that it has effectively lost three electrons to oxygen. In the lower oxide Ga2O, gallium has an oxidation state of +1.
In most of its compounds, gallium has an oxidation state of +3, though, in a few, it has an oxidation state of +1 (for example, in the oxide Ga2O). There is no evidence for authentic compounds of gallium in its +2 state. The ādihalides,ā for example, contain Ga+ and Ga3+ in a one-to-one ratio.
With the Group 15 (Va) elements nitrogen, phosphorus, arsenic, and antimony and the Group 13 elements aluminum and indium, gallium forms compoundsāsuch as gallium nitride (GaN), gallium arsenide (GaAs), and indium gallium arsenide phosphide (InGaAsP)āthat have valuable semiconductor and optoelectronic properties.
Gallium(III) ions resemble ferric iron (Fe3+) in size, charge, and coordination number, so they can be mistakenly taken up by cells and microorganisms via iron transport systems. Once taken up, gallium cannot undergo the normal redox reactions that iron participates in. As a result, it interferes with essential iron-dependent metabolic processes, disrupting respiration, DNA synthesis, and other biochemical pathways, thereby inhibiting the growth of rapidly proliferating cancer cells and bacteria. This mechanism of mimicking iron to gain entry and then blocking iron-dependent functions is often described as a Trojan horse strategy.
Some of these compounds are used in solid-state devices, such as transistors and rectifiers, and some form the basis for light-emitting diodes (LEDs) and semiconductor lasers. GaN nanowires have been synthesized and used in electronic and optoelectronic nanosystems (that is, extremely small electronic devices that use light in their operation).
Of the halides, only gallium trifluoride is ionic; the others have molecular lattices containing dimeric molecules, in which two identical molecular units are joined together, with the formula Ga2X6. The sulfide (GaS), selenide (GaSe), and telluride (GaTe), made directly by combination of the elements at high temperature, are diamagnetic and contain galliumāgallium units with four positive charges (GaāGa)4+, in a layer lattice. The hydroxide, formula Ga(OH)3, is amphoteric; it is precipitated from solutions of gallium salts by alkali hydroxides.