Question

What is meant by atomic radius? How does it vary down the group and why? How does it vary along a period and why?

Answer 1

Atomic radius:

The atomic radius of an element is defined as the distance between the nucleus and its atom’s outermost orbit.

Atomic size variation down the group:

• The atomic radius increases as the group progresses.
• This is due to the addition of more shells as one advance through the group.
• As a result, the distance between the outermost electrons and the nucleus grows; the atomic size grows despite the increase in nuclear charge.

Atomic size variation along the period:

• As the movement occurs from left to right along the period, the atomic radius decreases.
• This is due to a rise in nuclear charge, which attracts electrons to the nucleus and shrinks the atom's size.

Hence, the atomic radius increases down the group and decreases along the period.