Question

Write the electronic configuration of each one of Li (3), Na (11) and K (19) and answer the following question:

Which of these has the largest atomic radius?

Answer 1

Step-1: Introduction

The elements in periodic table are placed in periods and groups. Periods are horizontal rows that has increasing atomic numbers. Groups are vertical columns. There are 7 periods and 18 groups in periodic table.

Step-2: Electronic configuration

Atomic numbers of Lithium ($\mathrm{Li}$), Sodium ($\mathrm{Na}$) and Potassium ($\mathrm{K}$) are 3, 11 and 19 respectively.

Electronic configuration of Lithium = (2, 1).

Electronic configuration of Sodium = (2, 8, 1).

Electronic configuration of Potassium = (2, 8, 8, 1).

Step-3: Atomic radii

Atomic radii is the distance of the electrons in the outermost shell from the atomic nucleus.

It increases from top to bottom in a group and decreases from left to right in a period but is highest for a noble gas.

Since Lithium, Sodium and Potassium belongs to same group 1, atomic size rises. The reason is due to rise in shell number and it results in increase in atomic size. Lithium will have the lower atomic radii while Potassium have the greater radii.

Therefore, Potassium has the largest atomic radii.