Question

Generally the atomic and ionic radii increase with increase in atomic number down the group. But the atomic size of aluminium and gallium is almost the same. This is because

• A. The nuclear charge of $Ga$ is higher than that of $Al$
• B. Gallium contains intervening d-electrons which do not screen the valence electrons effectively
• C. The ionization energies of $Ga$ and $Al$ are comparable
• D. All the three above

Answer 1

The correct option is B Gallium contains intervening d-electrons which do not screen the valence electrons effectively

Due to the poor shielding (screening) effect of d-electrons in case of $Ga$, the valence electrons are attracted more strongly and hence the size is not increased much. Hence, the atomic size of aluminium and gallium is almost the same.