31
  Ga  
69.723000
Gallium

Name: Gallium
Symbol: Ga
Atomic Number: 31
Atomic Weight: 69.723000
Family: Boron Family
CAS RN: 7440-55-3
Description: A silvery white solid
State (25C): Solid
Oxidation states: +3

Molar Volume: 11.44 cm3/mole
Valence Electrons: 4p1

Boiling Point:  2676K, 2403C, 4357F
Melting Point:
303.05K, 29.9C 85.8F
Electrons Energy Level: 2, 8, 18, 3
Isotopes: 22 + 2 Stable
Heat of Vaporization: 258.7 kJ/mol
Heat of Fusion: 5.59 kJ/mol
Density: 5.907 g/cm3 @ 300K
Specific Heat: 0.37 J/gK
Atomic Radius: 1.81
Ionic Radius: 0.62
Electronegativity: 1.81 (Pauling); 1.82 (Allrod Rochow)
Gallium (Latin Gallia meaning Gaul (essentially modern France); also gallus, meaning "rooster") was discovered spectroscopically by Paul-Emile Lecoq de Boisbaudran in 1875 by its characteristic spectrum (two violet lines) in an examination of a Zinc blende from the Pyrenees.  Before its discovery, most of its properties had been predicted and described by Dmitri Mendeleev in 1871 (who called the hypothetical element ekaaluminum) on the basis of its position in his newly created Periodic Table of Elements.  Later, in 1875, Boisbaudran obtained the free metal through the electrolysis of a solution of gallium hydroxide (Ga(OH)3) in potassium hydroxide (KOH).  He named the element "gallia" after his native land of France.  It was later claimed that, in one of those multilingual puns so beloved of men of science of the early 19th century, he also named it after himself, as 'Lecoq' = the rooster, and Latin for rooster is "gallus"; however, he denied this in an 1877 article.

A soft silvery metallic poor metal, Gallium is a brittle solid at low temperatures but liquefies slightly above room temperature and will melt in the hand. It occurs in trace amounts in Bauxite and Zinc ores.  An important application is in the compound Gallium Arsenide, used as a semiconductor, most notably in light-emitting diodes (LEDs).

The detective work behind the isolation of Gallium depended on the recognition of unexpected lines in the emission spectrum of a zinc mineral, Sphalerite.   Eventual extraction and characterization followed.  Today, most Gallium is still extracted from this zinc mineral.

Trace amounts of gallium are also found in diaspore, germanite and bauxite as well as in the byproducts of burning coal.

5
B
10.81
13
Al
26.98
31
Ga
69.72
49
In
114.8
81
Tl
204.3

1s2 2s2p6 3s2p6d10 4s2p1

Characteristics

Gallium is one of four metals--Mercury (Hg), Cesium (Cs) and Rubidium (Rb)--which melts near room temperature and has one of the largest liquid ranges of any metal, so it has found use in high temperature thermometers.  At room temperature Gallium is as soft as lead and can be cut with a knife.  Its melting point is abnormally low and it will begin to melt in the palm of a warm hand.   Gallium is one of a small number of metals that expands when freezing.

Elemental Gallium is not found in nature, but it is easily obtained by smelting.   Very pure Gallium metal has a brilliant silvery color and its solid metal fractures conchiodally like glass.  Gallium metal expands by 3.1 percent when it solidifies, and therefore storage in either glass or metal containers is avoided, due to the possibility of container rupture with freezing.  Gallium shares the higher-density liquid state with only a few materials like Germanium, Bismuth and water.

1s2
2s2 2p6
3s2 3p6 3d10
4s2 4p1

Gallium also attack most other metals by diffusing into their metal lattice.   Gallium for example diffuses into the grain boundaries of Al/Zn alloys or steel.   Gallium metal easily alloys with many metals, and was used in small quantities in the core of the first atomic bomb to help stabilize the plutonium crystal structure.

The melting point temperature of 30C allows the metal to be melted in one's hand.   This metal has a strong tendency to supercool below its melting point/freezing point, thus necessitating seeding in order to solidify.  Gallium is one of the metals (with Caesium, Francium and Mercury) which are liquid at or near normal room temperature, and can therefore be used in metal-in-glass high-temperature thermometers.  It is also notable for having one of the largest liquid ranges for a metal, and (unlike Mercury) for having a low vapor pressure at high temperatures. Unlike Mercury, liquid Gallium metal wets glass and skin, making it mechanically more difficult to handle (even though it is substantially less toxic and requires far fewer precautions).  For this reason as well as the metal contamination problem and freezing-expansion problems noted above, samples of Gallium metal are usually supplied in polyethylene packets within other containers.

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 244 ppm) and six other neighbors within additional 39 pm.  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 are seen as the fundamental building blocks of the crystal.   The compound with Arsenic, Gallium Arsenide is a semiconductor commonly used in light-emitting diodes.

High-purity Gallium is attacked slowly by mineral acids. 

Occurrence

Gallium does not exist in free form in nature, nor do any high-gallium minerals exist to serve as a primary source of extraction of the element or its compounds.  Gallium is found and extracted as a trace component in bauxite, coal, diaspore, germanite, and sphalerite.  The USGS estimates Gallium reserves based on 50 ppm by weight concentration in known reserves of bauxite and zinc ores.  Some flue dusts from burning coal have been shown to contain as much as 1.5 percent gallium.

Most gallium is extracted from the crude Aluminum Hydroxide solution of the Bayer Process for producing alumina and Aluminum.  A Mercury cell electrolysis and hydrolysis of the amalgam with Sodium Hydroxide leads to Sodium Gallate.   Electrolysis then gives Gallium metal. For semiconductor use, further purification is carried out using zone melting, or else single crystal extraction from a melt (Czochralski Process).  Purities of 99.9999% are routinely achieved and commercially widely available.

The current price for 1 kg Gallium of 99.9999% purity seems to be at about $400.

Applications

Semiconductor and electronic industry.  The semiconductor applications are the main reason for the low-cost commercial availability of the extremely high-purity (99.9999+%) metal:

Wetting & Alloy Agent

Liquid Alloys

Biomedical Applications

Miscellaneous

Compounds

Gallium is often found as a trace element in Diaspore, Sphalerite, Germanite, Bauxite and Coal.  Gallium arsenide (GaAs) can produce laser light directly from electricity. Large amounts of gallium trichloride (GaCl3) have been gathered to build the Gallium Neutrino Observatory, an observatory located in Italy built to study particles called neutrinos which are produced inside the sun during the process of nuclear fusion.

Magnesium Gallate, MgGa2O4 Gallium Arsenide, GaAs
Gallium Nitrate, Ga(NO3)3 Sodium Gallate, Na2Ga2O4
Gallium Hydroxide, Ga(OH)3 Gallium Trichloride, GaCl3
Gallium Citrate, GaC6H5O7

Gallium Citrate2.jpg (17295 bytes)

Isotopes

atom.gif (700 bytes)

Isotope Atomic Mass Half-Life
Ga56 55.995  
Ga57 56.983  
Ga58 57.974  
Ga59 58.963  
Ga60 59.957  
Ga61 60.949 0.15 seconds
Ga62 61.9442 116.12 ms
Ga63 62.939 32.4 seconds
Ga64 63.9368 2.627 minutes
Ga65 64.9327 15.2 minutes
Ga66 65.9316 9.49 hours
Ga67 66.9282 3.2612 days
Ga68 67.928 67.629 minutes
Ga69 68.9256 Stable
Ga70 69.926 21.14 minutes
Ga71 70.9247 Stable
Ga72 71.9264 14.10 hours
Ga73 72.9252 4.86 hours
Ga74 73.9269 8.12 minutes
Ga75 74.9265 126 seconds
Ga76 75.9289 32.6 seconds
Ga77 76.9293 13.2 seconds
Ga78 77.9317 5.09 seconds
Ga79 78.933 2.847 seconds
Ga80 79.937 1.697 seconds
Ga81 80.938 1.217 seconds
Ga82 81.943 0.599 seconds
Ga83 82.947 0.31 seconds
Ga84 83.952 85 ms
Ga85    

Precautions

40px-Skull_and_crossbones.svg.jpg (1420 bytes) While not considered toxic, the data about gallium is inconclusive. Some sources suggest that it may cause dermatitis from prolonged exposure; other tests have not caused a positive reaction.

  Like most metals, finely divided gallium loses its luster. Powdered gallium appears gray. When gallium is handled with bare hands, the extremely fine dispersion of liquid Gallium droplets which results from wetting skin with the metal may appear as a gray skin stain.


atom.gif (700 bytes)

Gallium Data

Atomic Radius (): 1.81
Atomic Volume cm3/mol : 11.8cm3/mol
Covalent Radius: 1.26
Crystal Structure: Orthorhombic
Ionic Radius: 0.62

Chemical Properties

Electrochemical Equivalents: 0.8671 g/amp-hr
Electron Work Function: 4.2eV
Electronegativity: 1.81 (Pauling); 1.82 (Allrod Rochow)
Heat of Fusion: 5.59 kJ/mol
Incompatibilities: unknown
First Ionization Potential: 5.999
Second Ionization Potential: 20.51
Third Ionization Potential: 30.71
Valence Electron Potential: 69.7
Ionization Energy (eV): 5.999 eV

Physical Properties

Atomic Mass Average: 69.723
Boiling Point: 2676K, 2403C, 4357F
Melting Point: 303.05K, 29.9C 85.8F
Heat of Vaporization: 258.7 kJ/mol
Coefficient of Lineal Thermal Expansion/K-1: N/A
Electrical Conductivity: 0.0678 106/cm
Thermal Conductivity: 0.406 W/cmK
Density: 5.907 g/cm3 @ 300K
Enthalpy of Atomization: 276.1 kJ/mole @ 25C
Enthalpy of Fusion: 5.59 kJ/mole
Enthalpy of Vaporization: 256.1 kJ/mole
Flammability Class: unknown
Molar Volume: 11.44 cm3/mole
Optical Reflectivity: unknown
Optical Refractive Index: unknown
Relative Gas Density (Air=1): unknown
Specific Heat: 0.37 J/gK
Vapor Pressure: 9.31E-36 Pa @ 29.9C
Estimated Crustal Abundance: 1.9101 milligrams per kilogram
Estimated Oceanic Abundance: 310-5 milligrams per liter


(L. Gallia, France; also from Latin, gallus, a translation of Lecoq, a cock) Predicted and described by Mendeleev as ekaaluminum, and discovered spectroscopically by Lecoq de Boisbaudran in 1875, who in the same year obtained the free metal by electrolysis of a solution of the hydroxide in KOH. Gallium is often found as a trace element in diaspore, sphalerite, germanite, bauxite, and coal. Some flue dusts from burning coal have been shown to contain as much 1.5% gallium. It is the only metal, except for mercury, cesium, and rubidium, which can be liquid near room temperatures; this makes possible its use in high-temperature thermometers. It has one of the longest liquid ranges of any metal and has a low vapor pressure even at high temperatures. There is a strong tendency for gallium to supercool below its freezing point. Therefore, seeding may be necessary to initiate solidification. Ultra-pure gallium has a beautiful, silvery appearance, and the solid metal exhibits a conchoidal fracture similar to glass. The metal expands 3.1% on solidifying; therefore, it should not be stored in glass or metal containers, as they may break as the metal solidifies. Gallium wets glass or porcelain and forms a brilliant mirror when it is painted on glass. It is widely used in doping semiconductors and producing solid-state devices such as transistors. High-purity gallium is attacked only slowly by mineral acids. Magnesium gallate containing divalent impurities such as Mn+2 is finding use in commercial ultraviolet activated powder phosphors. Gallium arsenide is capable of converting electricity directly into coherent light. Gallium readily alloys with most metals, and has been used as a component in low-melting alloys. Its toxicity appears to be of a low order, but should be handled with care until more data are forthcoming. The metal can be supplied in ultrapure form (99.99999+%). The cost is about $3/g.

Source: CRC Handbook of Chemistry and Physics, 1913-1995. David R. Lide, Editor in Chief. Author: C.R. Hammond