Gallium (31)

Gallium 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.

Ultra-pure gallium has a beautiful, silvery appearance, and the solid metal exhibits a conchoidal fracture similar to glass. The metal expands on solidifying; therefore, it should not be stored in glass or metal containers, as they may break as the metal solidifies.

•Name: Gallium
•Symbol: Ga
•Atomic number: 31
•Atomic weight: 69.723 
•Standard state: solid at 298 K (but melts only slightly above this temperature)
•CAS Registry ID: 7440-55-3
•Group in periodic table: 13
•Period in periodic table: 4
•Block in periodic table: p-block
•Color: silvery white
•Classification: Metallic

Historical information

Gallium was discovered by Paul-Emile Lecoq de Boisbaudran at 1875 in France. Origin of name is from the Latin word "Gallia" meaning "France" and perhaps also from the Latin word "gallus" (the cock, a translation of Lecoq, the discoveror of gallium). Gallium was an element whose existence was predicted by Mendeleev in 1871. He predicted that the then unknown element gallium should resemble aluminum in its properties. He suggested therefore the name eka-aluminium (symbol Ea). His predictions for the properties of gallium are remarkably close to the reality. Gallium was discovered spectroscopically by Paul-Emile Lecoq de Boisbaudran in 1875, who in the same year obtained the free metal by electrolysis of a solution of the hydroxide Ga(OH)3 in KOH.

Physical properties

•Melting point: 302.91 [or 29.76 °C (85.57 °F)] K
•Boiling point: 2477 [or 2204 °C (3999 °F)] K

Orbital properties

•Ground state electron configuration: [Ar].3d10.4s2.4p1
•Shell structure: 2.8.18.3
•Term symbol: 2P1/2

Isolation

Gallium is normally a byproduct of the manufacture of aluminum. The purification of bauxite by the Bayer process results in concentration of gallium in the alkaline solutions from an aluminum:gallum ratio from 5000 to 300. Electrolysis using a mercury electrode gives a further concentration and further electrolysis using a stainless steel cathode of the resulting sodium gallate affords liquid gallium metal.

Very pure gallium requires a number of further processes ending with zone refining to make very pure gallium metal.

Interesting Facts:

Gallium (English, French, German, Swedish) Gallio (Italian) Galio (Spanish)

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.

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

29^th:
GERMANIUM (32)

Germanium is a gray-white semi-metal, and in its pure state is crystalline and brittle, retaining its luster in air at room temperature. It is a very important semiconductor material. Zone-refining techniques have led to production of crystalline germanium for semiconductor use with an impurity of only one part in 10-10.

Certain germanium compounds have a low mammalian toxicity, but a clear activity against certain bacteria, which makes them of interest as chemotherapeutic agents.

•Name: Germanium
•Symbol: Ge
•Atomic number: 32
•Atomic weight: 72.64
•Standard state: solid at 298 K
•CAS Registry ID: 7440-56-4
•Group in periodic table: 14
•Period in periodic table: 4
•Block in periodic table: p-block
•Color: greyish white
•Classification: Semi-metallic

Historical information

Germanium was discovered by Clemens Winkler at 1886 in Germany. Origin of name is from the Latin word "Germania" meaning "Germany". Germanium was an element whose existence was predicted by Mendeleev in 1871. He predicted that the then unknown element germanium should resemble silicon in its properties. He suggested therefore the name ekasilicon (symbol Es). His predictions for the properties of germanium are remarkably close to the reality. Germanium was discovered in a mineral called argyrodite by Clemens Alexander Winkler in 1886.

Physical properties

•Melting point: 1211.4 [or 938.3 °C (1720.9 °F)] K
•Boiling point: 3093 [or 2820 °C (5108 °F)] K
•Density of solid: 5323 kg m-3

Orbital properties

•Ground state electron configuration: [Ar].3d10.4s2.4p2
•Shell structure: 2.8.18.4
•Term symbol: 3P0

Isolation

There is normally no need to make germanium in the laboratory as it is readily available commercially. Germanium is available through the treatment of germanium dioxide, GeO2, with carbon or hydrogen. The extraction of germanium from flue dust is complex because of the difficulty in separating it from zinc, which is also present.

GeO2 + 2C → Ge + 2CO

GeO2 + 2H2 → Ge + 2H2O

Very pure germanium can be made by the reaction of GeCl4 with hydrogen.

GeCl4 + 2H2 → Ge + 4HCl

Interesting Facts about Germanium:

Germanium (English, French, German, Swedish)  Germanio (Italian/Spanish)

Trace impurities can be added to germanium to produce semiconductors.

Germanium and germanium oxide are transparent to infrared light and exhibit other desirable optical properties, so the element is used in infrared spectrometers and lenses.

Elemental arsenic occurs in two solid modifications: yellow, and grey or metallic, with specific gravities of 1.97, and 5.73, respectively. The element is a steel grey, very brittle, crystalline, semi metallic (metalloid) solid. It tarnishes in air, and when heated rapidly oxidizes to arsenous oxide which has a garlic odor.