Question

Why does ionic size increase down a group?

Answer 1

The size of the atom before becoming an ion is larger as the atoms go down in a group or family.

Explanation:

For the group I A and II A for an example the losing of an electron causes the atom to be smaller than tthe neutral atom. While this is true of all the elements in these families, the starting points are different.

Li after losing an electron goes to `1s^2` with all of its electrons left in the first shell.

Na after losing an electron goes to `1s^2 2s^2 2p^6` with all of its electrons left in the first and second shell.

Because the second shell is larger than the first shell the `Na^(+1)`
ion with be bigger than the `Li^(+1)`

This is the same for all families because each element in the family is in a larger shell as the elements go down on the Periodic Table.