ICSE Class 10 Answered

Concept:

 

The distance between the centre of the nucleus and the outermost orbit of the atom is called the atomic radius of the atom of an element.

Variation along the period: - The atomic radius decreases as we move from left to right along the period. This is due to an increase in nuclear charge which tends to pull the electrons closer to the nucleus and reduces the size of the atom.

Variation along the group: - The atomic radius increases down the group. This is because new shells are being added as we go down the group. This increases the distance between the outermost electrons and the nucleus so  the atomic size increases inspite of the increase in nuclear charge.