Indium atomic properties

For a discussion of the atomic properties of the group 13 metals see Downs AJ (1993) In Downs AJ (eds) Chemistry of aluminum gallium, indium and thallium. Blackie, London, Chapter 1... 

The gallium and indium atoms maintain their typical tricoordination and do not interact with carbon monoxide which interacts only with the transition metal atoms (manganese). Such a behaviour means that non-transition and transition metal atoms maintain their own properties even when directly bound also in a complex cluster cage. In agreement with this point in a compound as Sn[Co(CO)4] 2 [Mn(CO)s] 2 [137] the cobalt and manganese atoms maintain their typical coordination as the tin atom. 

The platinum-group metals (PGMs), which consist of six elements in Groups 8— 10 (VIII) of the Periodic Table, are often found collectively in nature. They are mthenium, Ru rhodium, Rh and palladium, Pd, atomic numbers 44 to 46, and osmium. Os indium, Ir and platinum, Pt, atomic numbers 76 to 78. Corresponding members of each triad have similar properties, eg, palladium and platinum are both ductile metals and form active catalysts. Rhodium and iridium are both characterized by resistance to oxidation and chemical attack (see Platinum-GROUP metals, compounds). 

Ununtrium is located on the periodic chart in group 13 (IIIA) just below thallium and indium. It is expected to have chemical and physical properties similar to these two homo-logues. Since only one or two unstable atoms of the isotopes of ununtrium have been synthesized, its melting point, boiling point, and density are not known. 

Using his table, Mendeleev was also able to correct several values of atomic masses. For example, the original atomic mass of 76 for indium was based on the assumption that indium oxide had the formula InO. This atomic mass placed indium, which has metallic properties, among the nonmetals. Mendeleev assumed that.the atomic mass was probably incorrect and proposed... 

Indium and thallium resemble white tin and lead in having atomic radii large compared with those of true metals of similar atomic number, and the explanation is again to be found in incomplete ionization arising from the stability of the lone pair of 5s and 6s electrons, respectively. As a result of this stability the elements behave in many respects as if they belonged to group 1, just as lead has many of the properties of a group 2 element. 

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... 

At this time the Periodic Classification had not been formulated and it was difficult to decide to which group of elements thallium should be assigned. The metal resembles lead in many of its physical properties and a number of thallous compounds likewise resembled those of lead. Other thallous salts were found to be isomorphous with those of potassium and the spectrum of thallium was simple like the spectra of the alkali metals. To add to the uncertainty, thallic compounds resembled those of aluminium. For these reasons Dumas referred to thallium as the paradoxical metal and the ornithorynchus of the metals . MendeMeff, with characteristic courage, classed thallium with the aluminium metals in his Periodic Table in 1869, and subsequent research has fully justified this arrangement. With an atomic number 81 it lies between mercury (80) and lead (82) and whilst in the monovalent state it shows analogy with the alkali metals, in the trivalent state it is a true congener of indium. 

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