THE ATOMIC VOLUME OF HYDROGEN IN METAL-HY DRIDES IN COMPARISON WITH CORRESPONDING FLUORIDES AND CHLORIDES

The atomic volume of hydrogen in metal hydrides is calculated by using the atomic volumes of the metal cations as given by Biltz. The except ional polarizability of hydrogen ligands is the reason for its adaptab ility when forming different bond structures in metal hydrides. The at omic volume of hydrogen decreases from 13.7 cm(3)mol(-1) in salt-like caesium hydride to 3.9 cm(3)mol(-1) in metallic palladium hydride. Thi s variation is significantly higher for metal hydrides than for metal chlorides, although the volume of a hydrogen ion is comparable to that of a fluoride ion, that shows an almost constant value in its compoun ds. For structurally related hydrides an examination of the atomic vol ume of hydrogen allows the re-examination of a given composition and t herefore the disclosure of a wrong atomic arrangement.