Question

Atomic radius of Ga ( $135 pm )$ is less than that of $Al (143 pm )$ because

• A. of the small variation in the inner core of the electronic configuration
• B. the presence of additional $10 d$-electrons which offers only poor screening effect for the outer electrons from the increased nuclear charge in gallium
• C. Both (a) and (b) are correct
• D. Neither (a) nor (b) is correct

Answer 1

Answer: (B)

The electrons in $d$-orbitals cannot screen the nucleus effectively and hence effective nuclear charge of $Ga$ (It contains $10$ electrons) is greater in magnitude than that of $Al$. So, electrons of Ga experience greater force of attraction than $Al$ and hence atomic radius of $Ga$ is lesser than that of $Al$.