There's been an unsolved mystery associated with mixed valence compounds: when the valence state of an element in these compounds changes with increased temperature, the number of electrons associated ...

Mixed-valence compounds — which have one or more of the same metal atoms in different oxidation states — are fairly common, with examples such as Fe 3 O 4 and Prussian blue being known for some time.

THESE lectures deal with the development of the theory of valency from its origin to the latest quantum-mechanical views on the subject. The subject is discussed concisely, but the exposition is clear ...