WAEC Chemistry 2014 Paper

Concept:Atomic radius generally decreases as we move from left to right across a period.This happens because the nuclear charge increases, pulling electrons closer to the nucleus.Explanation:The elements Li, Be, B, and C belong to the same period, Period 2.Their positions from left to right in the periodic table are:$$\mathrm{Li},\ \mathrm{Be},\ \mathrm{B},\ \mathrm{C}$$As the atomic number increases from 3 to 6, the effective nuclear charge also increases.The added electrons enter the same shell, so shielding remains nearly constant.Therefore, the atomic radius decreases steadily in this order.Hence, the correct decreasing order of atomic radius is:$$\mathrm{Li} > \mathrm{Be} > \mathrm{B} > \mathrm{C}$$Answer:C. $\mathrm{Li} > \mathrm{Be} > \mathrm{B} > \mathrm{C}$