Help with multiple choice A level chemistry question 😁

Hi I’m stuck with why the answer is C as in all of them the nuclear charge increases. Any help would be greatly appreciated many thanks xx :smile:

(edited 11 months ago)

Reply 1

user23184

Hi, to answer this question you would need to look at energy levels.

Period 3 contains the 3s and 3p orbitals, and as the 3s orbitals can only hold two electrons, Na and Mg are responsible for occupying the 3s1 and 3s2 orbitals respectively. However, as Al's electron is the first one to occupy the 3p orbital, it would require less energy to remove.
With sulphur, we need to look at Hund's rule to understand that electrons must fill empty orbitals before they pair up, therefore, S would have the first electron to pair up in the 3p energy level, and would therefore require less energy to remove due to the repulsion of the electrons in the same orbital.

With this in mind, we can observe that Al, Si, and P all have electrons that occupy an empty orbital each in the 3p energy level, with none pairing up. Therefore, the energy required to remove the electrons from each element would increase.