Question

Consider the elements Na, Mg and Al and their respective atomic numbers 11, 12 and 13. Write the electronic configuration of each element and answer the following answer:

Which element has the largest atomic radius?

Answer 1

Electronic configuration

Atomic numbers of Sodium ($\mathrm{Na}$), Magnesium ($\mathrm{Mg}$) and Aluminium ($\mathrm{Al}$) are 11, 12 and 13 respectively.

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

Electronic configuration of Magnesium = (2, 8, 2)

Electronic configuration of Aluminium = (2, 8, 3)

All these elements belong to period 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.

Sodium, Magnesium and Aluminium belongs to same period 3. Atomic size decreases across a period. This is due to an increase in the effective nuclear charge while moving across a period. Therefore, Sodium will have the higher atomic radii while Aluminium have the lower radii.

Therefore, Sodium has the largest atomic radii.