Gallium
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| General |
| Name, Symbol, Number |
gallium, Ga, 31 |
| Chemical series |
poor metals |
| Group, Period, Block |
13 (IIIA), 4 , p |
| Density, Hardness |
5904 kg/m3, 1.5 |
| Appearance |
silvery white |
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| Atomic properties |
| Atomic weight |
69.723 amu |
| Atomic radius (calc.) |
130 (136)pm |
| Covalent radius |
126 pm |
| van der Waals radius |
187 pm |
| Electron configuration |
[Ar]3d10 4s2 4p1 |
| e- 's per energy
level |
2, 8, 18, 3 |
| Oxidation states (Oxide) |
3 (amphoteric) |
| Crystal structure |
orthorhombic |
| Physical properties |
| State of matter |
Solid |
| Melting point |
302.91 K (85.57 °F) |
| Boiling point |
2477 K (3999 °F) |
| Molar volume |
11.80 ×10-6 m3/mol |
| Heat of vaporization |
258.7 kJ/mol |
| Heat of fusion |
5.59 kJ/mol |
| Vapor pressure |
9.31 E-36 Pa at
302.9 K |
| Speed of sound |
2740 m/s at 293.15 K |
| Miscellaneous |
| Electronegativity |
1.81 (Pauling scale) |
| Specific heat capacity |
370 J/(kg*K) |
| Electrical conductivity |
6.78 10-6/(m·ohm) |
| Thermal conductivity |
40.6 W/(m*K) |
| 1st ionization potential |
578.8 kJ/mol |
| 2nd ionization potential |
1979.3 kJ/mol |
| 3rd ionization potential |
2963 kJ/mol |
| 4th ionization potential |
6180 kJ/mol |
| Most stable isotopes |
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| SI units & STP are used except where
noted. |
Gallium is a chemical element in the periodic table that has the symbol Ga and atomic number 31. A rare, soft silvery metallic poor
metal, gallium is brittle at low temperatures but is liquid above room temperature and can indeed melt in the hand. It occurs
in trace amounts in bauxite and zinc ores.
Gallium arsenide is used as a semiconductor, most notably in light-emitting diodes (LEDs).
Notable characteristics
Very-pure gallium has a stunning silvery color and its solid metal fractures conchoidally like glass. Gallium metal expands by 3.1 percent when it
solidifies, and therefore should not be stored in either glass or metal containers. Gallium also corrodes most other metals by
diffusing into their metal lattice.
Gallium is one of four metals (with caesium, mercury, and rubidium) which are liquid at near
normal room temperature, and can therefore be used in high-temperature thermometers. It is also notable for having one of the largest liquid ranges for a metal, and for having a low
vapor pressure at high temperatures.
This metal has a strong tendency to supercool below its melting point,
thus necessitating seeding in order to solidify. High-purity gallium is attacked slowly by mineral acids. The melting point temperature is very low, T=30 °C, and the density is higher in the
liquid state than in the crystalline state (like in the case of water; the opposite effect is normally found for metals).
Gallium does not crystallize in any of the simple crystal structures. The stable phase under normal conditions is orthorhombic with 8 atoms in the conventional unit cell. Each atom has only one nearest neighbor (at a distance of 2.44 Å) and six other neighbors within
additional 0.39 Å. Many stable and metastable phases are found as function of temperature and pressure.
The bonding between the nearest neighbors is found to be of covalent character,
hence Ga2 dimers is seen as the fundamental building block of the crystal. The compound, gallium arsenide is a semiconductor commonly used in light-emitting diodes).
Applications
Analog integrated circuits are the most common application
for gallium, with optoelectronic devices (mostly laser diodes and light-emitting diodes) as the second largest end use.
Other uses include:
- Since it wets glass or porcelain, gallium is used to create brilliant
mirrors.
- Used widely to dope semiconductors and produce solid-state devices
like transistors.
- Gallium readily alloys with most metals, and has been used as a component in low-melting alloys. The plutonium pits of nuclear
weapons employ an alloy with gallium to stabilize of the allotropes of
plutonium. Much research is being devoted to gallium alloys as substitutes for mercury dental amalgams, but such compounds have yet to see wide acceptance.
Gallium added in quantities up to 2% in common solders can aid wetting and flow characteristics.
- Gallium is used in some high temperature thermometers, and a eutectic alloy of
gallium, indium, and tin is widely available in
fever thermometers, replacing mercury. This alloy, with the trade name Galinstan, has a freezing point of -20C.
- Magnesium gallate containing impurities (such as Mn+2), is
beginning to be used in ultraviolet-activated phosphor powder.
History
Gallium (Latin Gallia meaning "France"; also gallus, meaning "cock") was
discovered spectroscopically by Lecoq de Boisbaudran in 1875 by its characteristic spectrum (two
violet lines) in an examination of a zinc blend from the Pyrenees. Before its discovery, most of its properties had been predicted and described by
Dmitri Mendeleev (who called the hypothetical element
eka-aluminium) on the basis of its position in his periodic
table. Later in 1875, Boisbaudran obtained the free metal through the electrolysis of its hydroxide in KOH solution. He named the element after his native land of France
and, in one of those multilingual puns so beloved of men of science of the early 19th century, after himself, as 'Lecoq' = the rooster, and
Latin for rooster is "gallus".
Occurrence
Gallium does not exist in pure form in nature, nor are gallium compounds a primary source of extraction. It is rather found
and extracted as a trace component in bauxite, coal, diaspore, germanite, and sphalerite. The USGS estimates gallium reserves
based on 50 ppm concentration in known reserves of bauxite and zinc ores. Some flue dusts from burning coal have been shown to
contain as much 1.5 percent gallium.
Precautions
Gallium, while not considered toxic, can sometimes cause dermatitis from
prolonged exposure.
References
External links
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