Answer:
The last option, option D is correct.
The order of increasing ionic radii of the three ions given is
Na⁺ < F⁻ < Cl⁻
Check Explanation for reasons why.
Explanation:
For elements in the same group of the periodic table, the ionic radii increases as we move down the group. This is because the number of shells increase as we move further down a group in the periodic table and that automatically confers a bigger radii to the element with the more shells.
So, between F⁻ and Cl⁻, we know the fluoride ion has electronic configuration 2, 8 (2 shells) after it gains an electron to its normal electronic configuration to form the ion, but the chloride ion has electronic configuration 2, 8, 8 (3 shells) when it achieves its own stable octet of outermost electrons.
So, it is clear how Cl⁻ ion has a bigger ionic radii than F⁻ and even Na⁺.
Then, to know which ion is bigger between Na⁺ and F⁻, it is known that when cations and anions have the same electronic configuration, the cations usually have the lesser ionic radii.
This is because in a normal, neutral atom, the number of electrons in the atom matches the number of protons. And the force of attraction between the protons and the electrons matches each other as they both have the same charges and are equal in number.
But cations result from the neutral element losing one or more electrons to achieve that stable octet. This makes the number of protons to exceed the number of electrons, hence, the electrons available are more tightly pulled towards the centre of the atom by the protons in the nucleus of the atom. This results in a reduced ionic radii.
Unlike anions that gain electrons to achieve that stable octet and have the electrons exceeding the protons in their ions, causing the pull of the protons on the electrons to be reduced, thereby resulting in a more repelled electrons pushing the ionic radii further than normal thereby increasing it.
Hope this Helps!!!
