the others are endothermic and plumbane PbH4. the last hydride in
the group, is almost too unstable to exist at all. (We shall note some
of the methods needed to prepare these less stable hydrides in later
chapters.) Since the stability of the typical hydride (i.e. that in which
the element shows its group valency) falls off. it is hardly surprising
to find that the lower elements in a group do not form families of
hydrides (for example, in Group IV carbon and silicon form
numerous hydrides, germanium forms a few. tin forms one (stannane.
SnHJ and lead just manages to form PbH4).
The most important trend to be noted in the covalent hydrides is
the change in acid-base behaviour as we cross a period from
Group IV to Group VII. In Period 1, we have