Question

How does the atomic size vary along a group and a period? Give reasons and explain with the help of an example.

Answer 1

1. The size of an atom depends on the distance between the valence shell and the nucleus i.e., atomic radius.
2. Top to bottom in a group - The atomic radius increases as we move down the group as new shells are added.
3. For example - In group IA atomic radius increases in the order $\mathrm{Li}<\mathrm{Na}<\mathrm{K}<\mathrm{Rb}<\mathrm{Cs}$
4. Left to right along a period - The atomic radius decreases as we move left to right along a period because the electrons are added in the same shell. Hence, the effective nuclear charge increase. Due to which atomic radius decreases.
5. For example - In a period 2 atomic radius decreases in the order $\mathrm{Li}>\mathrm{Be}>\mathrm{B}>\mathrm{C}>\mathrm{N}>\mathrm{O}>\mathrm{F}$