Question

In the pair which species has a larger size? Explain

K + K⁺

Answer 1

K is larger in size than K⁺

The electronic configurations of K and K⁺ are:

K: 1s², 2s² 2p⁶, 3s², 3p⁶, 4s¹

K⁺: 1s², 2s², 2p⁶, 3s², 3p⁶

K⁺ is formed from K when the latter loses its 4s electron

K → K⁺ + e^-

As seen form the electronic configurations of K and K⁺, the K⁺ ion has 18 electrons and K atom has 19 electrons but the nuclear charge in the both these species is the same (+19). Since K⁺ ion has 1 electron less than K atom, the forces of attraction between the nucleus and the electrons are more stronger in K⁺ ion than in K atom. This results is more inward pulling of electron towards the nucleus in K⁺ ion and hence its size decreasees.