Atomic size down group 13 elements.

The elements in group 13 ( p-block) have smaller atomic radius compared to the s block elements . However, the trend in atomic radius do not vary in a regular manner down the group. The atomic radius of Ga (135 pm) is slightly less than that of Al ( 143 pm) . This is because Ga follows the d-block elements and inner core of Ga contains 10 “d” electrons that do not shield the nuclear charge efficiently. Therefore, the effective nuclear charge of Ga is more is more than that of Al so the outer electrons are attracted towards the nucleus and the size is smaller than expected.