Ionisation energies INCREASE across a period
This is because:
-
element x has a greater nuclear charge (more protons).
-
element x has a smaller atomic radius.
-
element x has greater nuclear pull so nuclear attraction increases.
Elements that are in the same shell experience the same shielding.
Ionisation energies DECREASE down groups
This is because:
-
element x has a bigger atomic radius (more shells).
-
element x has more shielding.
-
element x has less nuclear pull (increased shielding and distance outweighs increased nuclear charge) so nuclear attraction decreases.
For example, Group 2:
Atomic radius INCREASES across a period
This is because:
-
element x has more protons.
-
element x has a greater nuclear pull so nuclear attraction increases.
Atomic radius is the same if electrons are in the same shell so experience the same shielding.
Atomic radius INCREASES down groups
This is because:
-
the number of electron shells increase.
