The effects of electron retention and spin pair bonding on crystal cohesion in insulator oxides and halides

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Abstract
Ionization for salts in aqueous solution tends to equal formal valence (e.g., thorium can exist in solution as Th4+). However, as shown using lattice energy and melting point data, ionization in oxide or halide crystals does not exceed the number of s state electrons per metal atom (e.g., thorium in ThO2 has a formal valence of 4 and yet exhibits a cation ionization level of 1.9). Low values of ionization may be associated with internal coupling, electron transfer between metal atoms, and/or electron pairing between atoms that can form anions. The latter is likely to occur when the cations are small. When atoms that can form anions share electrons, they exhibit a reduced ‘‘demand’’ for charge from the metal atoms present. This results in a weaker bond and in the melting point decreasing logarithmically (rather than increasing) as bond length decreases.