Question

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

Which element is least reactive?

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 the K shell which can bear up to 2 electrons, the L shell which can bear up to 8 electrons and the M shell which can bear up to 18 electrons and so on.

3. The electronic configuration of Na, Mg and Al 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 $\mathrm{Na}$, Magnesium $\mathrm{Mg}$, and Aluminium $\mathrm{Al}$,

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

Hence, $\mathrm{Al}$ is the least reactive among $\mathrm{Na},\mathrm{Mg},$ and $\mathrm{Al}.$