Question

Which of the following statements BEST describes the first ionization energies of sodium compared to potassium?

• A. The first ionization energy for sodium is greater than the first ionization energy for potassium due to decrease in the effective nuclear charge.
• B. The first ionization energy for sodium is less than the first ionization energy for potassium due to decrease in the effective nuclear charge.
• C. The first ionization energy for sodium is greater than the first ionization energy for potassium due to a decrease in nuclear shielding.
• D. The first ionization energy for sodium is less than the first ionization energy for potassium due to a decrease in nuclear shielding.

Answer 1

The correct option is A The first ionization energy for sodium is greater than the first ionization energy for potassium due to decrease in the effective nuclear charge.

The Potassium lone electron is farther away from the nucleus than the Sodium lon electron. So there is a less nuclear force to hold the Potassium electron, hence it can be ionized easier.

The Potassium electron is in the fourth orbital, so there are three orbitals between it and the nucleus.

The outer electron in Potassium is in the $4s$ orbital, which is further away from the nucleus than the $3s$ orbital of the Sodium. This means that less energy is needed to remove the outermost electron and therefore the ionisation energy is lower.