Gallium
Ga
Atomic No. - 31
Gallium metal expands by 3.1% when it solidifies, and therefore
should not be stored in either glass or metal containers.
The History Says
Gallium was discovered spectroscopically by Lecoq de Boisbaudran in
the year 1875 by its characteristic spectrum, i.e. two violet lines,
in an examination of a zinc blend from the Pyrenees.
The Present Scenario
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.
Gallium
is a rare, soft silvery metallic poor metal which is a brittle solid
at low temperatures and turns to liquid state slightly above room
temperature, thus melting in hand. Gallium occurs in a trace amount in
bauxite and zinc ores.
Like water, it expands while freezing, becoming less dense. Though
gallium is non-toxic, but studies have showed that it is even not
useful to living organisms. It can corrode most metals by diffusing
into their metal lattice. Gallium do not crystallizes in any of the
simple crystal structures. Under normal conditions, the stable phase
is orthorhombic with 8 atoms in the conventional unit cell.
The name 'gallium' is supposed to be derived from the Latin word for
France, Gallia. Another theor suggests that Paul-Emile Lecoq de
Boisbaudran, the discoverer of Gallium has taken the name from the
Latin word 'gallum,' which mean 'the cock,' can be from his own name,
Lecoq.
Physical Properties of Gallium
| Phase |
Solid |
| Density (near room temperature) |
5.91 g/cm3 |
| Liquid density at melting point |
6.095 g/cm3 |
| Melting point |
302.9146 K (29.7646°C,
85.5763°F) |
| Boiling point |
2477 K (2204°C, 3999°F) |
| Heat of fusion |
5.59 kJ/mol |
| Heat of vaporization |
254 kJ/mol |
| Heat of capacity |
(25°C) 25.86 J/(mol-K) |
Atomic Properties of Gallium
| Crystal structure |
Orthorhombic |
| Oxidation states |
3 (amphoteric oxide) |
| Electronegativity |
1.81 (Pauling scale) |
| Ionization energies |
1st: 578.8 kJ/mol
2nd: 1979.3 kJ/mol
3rd: 2963 kJ/mol |
| Atomic radius |
130 pm |
| Atomic radius (calc.) |
136 pm |
| Covalent radius |
126 pm |
| Van der Waals radius |
187 pm |
Uses of Gallium
- In
integrated circuits with optoelectronic devices.
- In
creating brilliant mirrors.
- To
dope semiconductors and produce solid-state devices such as
transistors.
- As
a component in low-melting alloys.
- In
some high temperature thermometers.
- Gallium
salts such as gallium citrate and gallium nitrate are used in
medical imaging as radiocontrast agents.
Substitutes and Alternative Sources of
Gallium
Silicon is being used for GaAs in solar cell applications. Gallium
deposits are not going to run short in foreseeable future, but zinc
deposits, as alternative sources, may sometime in future become
important when easily accessible sources are used up.
Note:- Gallium arsenide circuits are very specialized and
do not have a substitute.
Occurrences of Gallium
- France
(leading refiner of gallium metal)
- Russia
- Canada
- Kazakhastan
|
