Gallium properties

Gallium [7440-55-3] atomic number 31, was discovered through a study of its spectral properties in 1875 by P. E. Lecoq de Boisbaudran and named from Gallia in honor of its discoverer s homeland. The first element to be discovered after the pubHcation of Mendeleev s Periodic Table, its discovery constituted a confirmation of the Table which was reinforced shordy after by the discoveries of scandium and germanium. 

Gainum (I)—Gallium (HI) Compounds having the formula Ga2X where X = Cl, Bt, or I, ate known. The stmcture of these mixed valance compounds, Ga" (GaX4) , has been better understood in recent years (26,27). Some properties ate Hsted in Table 5. Other compounds such as Ga" (Ga2X2) , where X = Cl or Bt, have also been identified and the stmctures determined (28,29). 

Unlike boron, aluminum, gallium, and indium, thallium exists in both stable univalent (thaHous) and trivalent (thaUic) forms. There are numerous thaHous compounds, which are usually more stable than the corresponding thaUic compounds. The thaUium(I) ion resembles the alkaU metal ions and the silver ion in properties. In this respect, it forms a soluble, strongly basic hydroxide and a soluble carbonate, oxide, and cyanide like the alkaU metal ions. However, like the silver ion, it forms a very soluble fluoride, but the other haUdes are insoluble. Thallium (ITT) ion resembles aluminum, gallium, and indium ions in properties. 

Triflates of aluminum, gallium and boron, which are readily available by the reaction of the corresponding chlorides with triflic acid, are effective Fnedel-Crafis catalysis for alkylation and acylation of aromatic compounds [119, 120] Thus alkylation of toluene with various alkyl halides m the presence of these catalysts proceeds rapidly at room temperature 111 methylene chloride or ni-tromethane Favorable properties of the triflates in comparison with the correspond mg fluorides or chlorides are considerably decreased volatility and higher catalytic activity [120]... 

Table 7.2 Comparison of predicted and observed properties of gallium...

The person whose name is most closely associated with the periodic table is Dmitri Mendeleev (1836-1907), a Russian chemist. In writing a textbook of general chemistry, Mendeleev devoted separate chapters to families of elements with similar properties, including the alkali metals, the alkaline earth metals, and the halogens. Reflecting on the properties of these and other elements, he proposed in 1869 a primitive version of today s periodic table. Mendeleev shrewdly left empty spaces in his table for new elements yet to be discovered. Indeed, he predicted detailed properties for three such elements (scandium, gallium, and germanium). By 1886 all of these elements had been discovered and found to have properties very similar to those he had predicted. 

After spending considerable time perusing the crumbling pages of late nineteenth-century chemistry journals and textbooks, I have confirmed the traditional account Mendeleev s periodic law attracted little attention. . . until chemists started to discover some of the elements needed to fill the gaps in his table and found that their properties were remarkably similar to those he had predicted. The frequency with which the periodic law was mentioned in-journals increased sharply after the discovery of gallium, most of that increase was clearly associated with Mendeleev s prediction of the properties of the new element, (p, 617)20... 

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