Question

Compare the radii of two species X and Y. Give reasons for your answers.

(a) X has 12 protons and 12 electrons

(b) Y has 12 protons and 10 electrons

Answer 1

Step 1: Atomic Radius

1. Atomic radius is the total distance of an atom from the center of the nucleus to the outermost shell of the element.

Step 2: Comparison of atomic radius:

1. The atomic radius of an atom depends on the shielding effect of the inner electrons in the atom. The shielding effect or screening effect is the reduction of nuclear attraction experienced by the valence electrons due to the presence of electrons in the inner orbital. This is because, in a multi-electron atom, there is a repulsive force between the electrons along with the attractive nuclear charge.
2. As the number of electrons in an atom increases, this repulsive force also increases. This causes a decrease in the effective nuclear charge experienced by the valence electrons. The atomic radii are inversely proportional to the nuclear charge experienced by the outer electrons in an atom.
3. Therefore, as the number of electrons in an atom increases, the effective nuclear charge on the outer electrons decreases, and atomic radii increase.
4. X and Y have an equal number of protons. Y has 10 electrons whereas X has 12 electrons. The shielding effect is higher in X due to the increase in the number of electrons. Therefore, the effect of the nuclear charge of Y is more and the atomic radius of Y is less than X.