Question

The $I{P}_1$ value of potassium is less than the $I{P}_1$ value of sodium. This is due to :

• A. large size of potassium atom
• B. small size of potassium atom
• C. low density of potassium
• D. univalent nature of potassium

Answer 1

Answer: (A)

large size of potassium atom

The outer electron in potassium is in the $4s$ orbital, which is further away from the nucleus than the $3s$ orbital of the sodium.

The greater distance means that the attraction between the electron is weaker.

The electron in Potassium is also more affected by shielding due to more shells, further weakening this attraction. This means that less energy is needed to remove the outermost electron and therefore the ionisation energy is lower.

Therefore, $I{P}_1$ value of $K$ < $I{P}_1$ value of $Na$.

Hence, option A is correct.