Question

Based on their positions in the periodic table, rank the following atoms or compounds in order of increasing first ionization energy:$\mathbf{M}\mathbf{g},\mathbf{O},\mathbf{S},\mathbf{S}\mathbf{i}$.

Short answer

$Mg<Si<S<O$

Step-by-step solution

Ionisation energy along with the group from top to bottom

Moving from top to bottom along a group in the periodic table increases the atomic size, leading to the decrease in ionization energy of the respective elements that belong to the same group.

Ionisation energy along with the period from left to right

Moving from left to right along a period in the periodic table decreases the atomic size, leading to the increase in ionization energy of the respective elements that belong to the same period.

Ranking the given elements in order of increasing the first ionization energy 

Among the given atoms, Mg, Si, and S belong to the same period, that is, the third period.

The atomic size order is $Mg>Si>S$.

The oxygen atom belongs to the second period. Hence, oxygen has the smallest size, and hence, it has the greatest ionization energy.

Thus, the order of ionization energy is:

$Mg<Si<S<O$