Gallium

Gallium

Gallium is a chemical element with symbol Ga and atomic number 31. Elemental gallium does not occur in nature, but as the gallium(III) compounds in trace amounts in bauxite and zinc ores. A soft silvery metallic poor metal, elemental gallium is a brittle solid at low temperatures. Held long enough, gallium will melt in the hand as it liquefies at temperature of 29.76 °C (85.57 °F) (slightly above room temperature). Its melting point is used as a temperature reference point. The alloy Galinstan (68.5% Ga, 21.5% In, 10% Sn) has an even lower melting point of −19 °C (−2 °F), well below the freezing point of water. From its discovery in 1875 until the semiconductor era, gallium was used primarily as an agent to make low-melting alloys.

Today, almost all gallium is used for microelectronics. Gallium arsenide, the primary use of gallium, is used in microwave circuitry and infrared applications. Gallium nitride and indium gallium nitride, minority semiconductor uses, produce blue and violet light-emitting diodes (LEDs) and diode lasers.

Gallium has no known role in biology. Because gallium(III) and ferric salts behave similarly in biological systems, gallium ions often mimic iron ions in medical applications. Gallium-containing pharmaceuticals and radiopharmaceuticals have been developed.

Occurrence

Gallium does not exist in free form in nature, and the few high-gallium minerals such as gallite (CuGaS2) are too rare to serve as a primary source of the element or its compounds. Its abundance in the Earth's crust is approximately 16.9 ppm. Gallium is found and extracted as a trace component in bauxite and to a small extent from sphalerite. The amount extracted from coal, diaspore and germanite in which gallium is also present is negligible. The United States Geological Survey (USGS) estimates gallium reserves to exceed 1 million tonnes, 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 small quantities of gallium, typically less than 1% by weight.

Symbol		Ga
Atomic Number		31
Atomic Weight		69.723
Oxidation States		+3
Electronegativity, Pauling		1.81
State at RT		Solid, Metal
Melting Point, K		302.93
Boiling Point, K		2676

Appearance and Characteristics

Harmful effects:

Gallium is considered to be non-toxic.

Characteristics:

• Gallium is a silvery, glass-like, soft metal. It sits close to the non-metals in the periodic table and its metallic properties aren’t as obviously metallic as most other metals. Solid gallium is brittle and is a poorer electrical conductor than lead.
• The solid metal fractures conchoidally. (Conchoidally means like a shell – the fractured surfaces are curved like a sea shell.)
• Gallium has the second largest liquid range of any element and is one of the few metals that is liquid near room temperature (m.pt. 29.76 oC, 85.6 oF ), melting in the hand.
• The other metals with this property are cesium, francium and mercury.
• Bromine is the only non-metallic element that is liquid at or around room-temperature.
• Gallium liquid clings to or wets glass and similar surfaces.
• Gallium also has the unusual property that (like water) it expands as it freezes.
• Four other elements expand when they freeze; silicon, bismuth, antimony and germanium

Uses of Gallium

• Low melting gallium alloys are used in some medical thermometers as non-toxic substitutes for mercury.
• Gallium arsenide is used in semiconductor production mainly for laser diodes, light-emitting diodes and solar panels. It is also used to create brilliant mirrors.