Chapter 28, Problem 11Q

To determine

The variation of atomic size with atomic number.

Answer to Problem 11Q

Solution:

Major changes in size are induced mostly due to addition of new shells, i.e., principal quantum number, and size saturates as we go down.

Explanation of Solution

As the atomic number of an element increases by one, there is addition of an electron. However, the nuclear charge also increases, and effectively reduces the atomic radius/size. This is seen in the periodic table when size reduces from left to right.

There is an increase in size when a new shell is added, as a new series of orbitals is used. However, in the 6th period onwards, the inner transition series contractions – Lanthanoid and Actinoid contractions offset these gains, and size of atom stop reducing.