Indium fundamental properties

The chlorides of indium are of considerable historical interest. Kekul regarded valency as a fundamental property of the atom, as unchangeable and invariable as the atomic weight. This view he retained to the last. Apparent exceptions certainly existed. Carbon monoxide could, however, readily be explained on the assumption that the two unused valencies of the carbon atom saturate each other mercurous salts, such as the chloride, possessed the double formula, Cl-Hg-Hg-Cl, and so on. In 1888, however, Nilson and Pettersson showed that three distinct chlorides of indium can exist in the vapour state. To these they gave the formulas InCl, InCl2 and... 

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