The Group I elements (Li to Cs) and Group II elements (Be to Ba) are s-block elements
(i) State and explain how the first ionisation energy of the elements vary from Group I to Group II and down the groups
A : From Group I to II
B : Down the groups
Ionization Energy is the minimum amount of energy required to remove an electron from the outermost shell of a neutral or gaseous atom.
A. Group II elements have slightly higher Ionization Energies compared to their corresponding group I elements.
This is because group II elements have smaller atomic sizes due to a greater nuclear charge than corresponding group I elements. As one moves from group I to group II in each period, the outer shell electrons become more strongly attracted to the nucleus hence require slightly more energy to remove.
B. Ionization Energy decreases down group I and group II elements.
This is due to an increase in atomic size (radius) caused by the successive increase in the number of electrons filled energy levels/shells as one moves down each group. as the atomic sizes increase, the outer shell electrons become loosely attracted to the positive nucleus, hence can easily be removed.