Question

Consider the elements Na, Mg and Al and their respective atomic numbers 11, 12 and 13.

Which element has the largest atomic radius?

Answer 1

Electronic configuration:

1. The arrangement of electrons in the atomic orbitals of elements is characterized by electronic configuration.
2. The atomic numbers are filled in K shell which can bear up to 2 electrons, L shell which can bear up to 8 electrons and M shell which can bear up to 18 electrons and so on.
3. The electronic configuration of Sodium $\left(\mathrm{Na}\right)$, Magnesium $\left(\mathrm{Mg}\right)$, and Aluminium $\left(\mathrm{Al}\right)$, can be obtained as:

$$\begin{gathered} \mathrm{Na}-2,8,1 \\ \mathrm{Mg}-2,8,2 \\ \mathrm{Al}-2,8,3 \end{gathered}$$

4. As increase the valence electron, the reactivity of the element decreases. So in Sodium $\left(\mathrm{Na}\right)$, Magnesium $\left(\mathrm{Mg}\right)$, and Aluminium $\left(\mathrm{Al}\right)$.

5. Aluminium has the most number of valence electrons-3.

Atomic radius:

1. Atomic radius decreases along the period of periodic table due to increase in effective nuclear charge and increases down the group due to increase in number of shells down the group.
2. Therefore, least effective nuclear charge acts on sodium as among Na, Mg, and Al, Na is the earliest in period 3. Thus, it will have the largest radius.

So, $\mathrm{Na}$ has the largest atomic radius.