Question

How does shielding effect atomic radius?

Answer 1

Down a group, the atomic radius increases as the nuclear shielding increases. Across a periodic, the atomic radius decreases as the nuclear shielding stays the same.

Explanation:

1. Down a Group
   • The atomic radius increases for several reasons.
   (a) As you move down a group, the number of energy levels
   increases by 1. This makes the atom larger.
   (b) This increasing number of energy levels increases the nuclear shielding. This means that outer e- feel less pull towards the positive nucleus as they are protected by filled, inner e- shells.

2. Across a Period
   • The atomic radius decreases for several reasons.
   (a) As you move L to R across the periodic table, the number of energy levels stays the same. Thus, the e- are not further away from the nucleus and feel its pull.
   (b) As such, the nuclear shielding also remains the same: the outer e- are protected by the same number of filled inner e- shells.
   (c) However, the nuclear charge (i.e. # of p+) increases. As the nucleus becomes more positive, it pulls the e- in closer, decreasing the atomic radius.