Question

How do atomic size vary in a period and in a group? How do you explain the variation?

Answer 1

• Within the group, the atomic size increases down the group. This is because a new energy shell is added at each succeeding element while the number of electrons in the valence shell remains to be the same.
• Therefore, the electrons added successively lie far away from the nucleus. The force of attraction of nucleus decreases in electrons,so the atomic size increases. In a period, the electrons are added to the same nucleus, so the nuclear charge increases with each successive element.
• This causes increase in force of attraction of nucleus resulting in decrease of atomic size.