The monovalent iodine, for instance, is transformed by heating into an allotropic form, corresponding to the formula I, whereas ordinary iodine answers to I 2.
They show varying permeability to a range of monovalent and divalent cations.
This compound may be considered as derived from methane, CH 4, by replacing a hydrogen atom by the monovalent group CH 3, known as methyl; hence ethane may be named " methylmethane."
The chlorine is not completely precipitated by silver nitrate in nitric acid solution, the ionization apparently not proceeding to all the chlorine atoms. Thallic iodide, T11 3, is interesting on account of its isomorphism with rubidium and caesium tri-iodides, a resemblance which suggests the formula T11 (12) for the salt, in which the metal is obviously monovalent.
Thus we have salts of the following types M20(W03)n, where n=1, 2, 3, 4, 5, 6, 7, 8, and also (M20)m(W03)n, where m, n=2, 5; 3, 7; 4, 3; 5, 12; M standing for a monovalent metal.