Chapter 28, Problem 18Q

To determine

The large difference in the ionization energy for Neon and Sodium.

Answer to Problem 18Q

Solution:

The large difference in the ionization energy for Neon and Sodium is because Neon is a noble gas and loses stable configuration. Therefore, it has high ionisation energy. Sodium gains a noble gas configuration by ionisation, so has low ionisation energy.

Explanation of Solution

From electronic configurations we can see that Sodium has one electron in the 3s orbital. If it was to lose that, it would have completely filled shells, i.e., noble gas configuration. It is energetically beneficial for it to lose one electron, so it has low ionisation energy.

$\begin{array}{l}Na\to 1s^{2}2s^{2}2p^{6}3s^1\\ Ne\to 1s^{2}2s^{2}2p^6\end{array}$

We get to see that in case of Neon, the element already has completely filled shells and thus is in a lower energy state. Ionisation would increase its energy, which is not beneficial to it. Therefore, we see high ionisation energy in case of Neon.