Binary hydrides can be classified according to the position of the element in the
periodic table, and by the bond characters. The hydrides of alkali and alkaline earth
metals among s-block elements are ionic compounds structurally analogous to halides
and are called saline hydrides. The Group 13-17 p-block elements form covalent
molecular hydrides. No hydride of rare gas elements has been reported.
Some of the d-block and f-block transition metals form metal hydrides exhibiting
metallic properties. Transition metals which do not give binary hydrides form many
molecular hydride complexes coordinated by stabilization ligands, such as carbonyl
(CO), tertiaryphosphines (PR3), or cyclopentadienyl (C5H5) (refer to Section 6.1). Typical hydrides of each class are given below.