When Dimitri Mendeleev first produced his periodic table in 1871 there were a number of gaps where elements were at the time undiscovered. To one of these gaps, at atomic number 31, Mendeleev assigned the element the provisional name of ekaaluminum. Four years later the French chemist Paul-Emile Lecoq de Boisbaudran found a new element, to which he gave the name gallium, to fill this gap. He first found the element spectroscopically before later in the same year producing the pure metal by the hydrolysis of a solution of gallium hydroxide in potassium hydroxide.
The element he discovered has an atomic weight of 69.723 and a density of 5.91 grams per cubic centimeter. The ionization energy of gallium is 5.999 eV and its oxidation state is +3.
The generally accepted source of the elements name is the Latin name for Lecoq de Boisbaudran’s home country of France, the Latin name for France being “Gallia”. An alternative to this is play on words relevant to the founder’s name Lecoq is French for cockerel and the Latin for this is “gallus”.
The bright silver colored metal gallium is almost liquid at room temperature. In fact, on a hot summer’s day in a room with no air-conditioning it is a liquid. This element’s melting point is just 302.91 K (29.76 C, 85.57 F). With a boiling point of 2477 K (2204 C or 3999 F), gallium has one of the largest liquid ranges of any element. This liquid range allows the use of gallium in high temperature thermometers. In addition to its liquid range, gallium has a low vapor pressure even at high temperatures.
Once liquefied, the element tends to supercool. Therefore, it remains liquid below its freezing point. The addition of seed particles of solid gallium is sometimes required to get the supercooled metal to solidify. As it solidifies, gallium expands 3.1 %. This means that the liquid gallium should not be stored in filled glass or metal containers as such vessels break as the metal expands.
Gallium has a rhombohedral crystal structure. If fractured the metal exhibits a conchoidal fracture similar to that of glass.
Gallium “wets” both porcelain and glass. Gallium when painted on to glass forms a brilliant mirror.
One of gallium’s compounds, gallium arsenide, has an unusual property. When subjected to an electrical current this compound produces coherent or laser light.
Recently another compound gallium trichloride has proved useful in the field of particle physics. The Gallium Neutrino Observatory based at Italy’s Laboratori Nazionali del Gran Sasso is using 101 tons of the compound to detect neutrinos produced by nuclear fusion in the sun.
Los Alamos National Laboratory Chemistry Division
Jefferson Laboratories Science Education website
National Institute of Nuclear Physics