The outermost orbital of s block elements consists of one or two
electrons. Next to the outer most penultimate shell has either 2 or 8 electrons.
s-block elements show a fixed valency which depends on the number of electrons
present in the outermost shell.
Except hydrogen , all s-block elements have low values of ionisation
potential decreases in the case of alkali metals and alkaline earth metals as
the atomic number increases. Ionisation potential increases on moving
horizontally from IA to IIA. On account of low values of ionisation potentials ,
these elements are highly electropositve , i.e., easily lose valency electrons
and form cations.
The elements of groups of p block elements exhibit a range of properties. Many
of the trends observed in this group can be understood from considerations of
their electron configurations and their respective positions in the periodic
table. For example, the inert pair of valence-shell electrons retained in the Ti+ ion
is also found in several other cations following a transition series.