Question

Why is the first ionization energy of the transition elements reasonably constant?

Answer 1

Answer:

Due to the addition of more e−

s in the same d-subshell, the e−

suffers repulsion due to which their ionic radii does not decrease appreciably on moving from left to right hence, ionization energy also remains almost constant.

Answer 2

The first ionization energy of the transition elements increases with increase in atomic number across a given transition series, although the increase is rather slow and hence, it becomes reasonably constant.

• The increase in ionization enthalpy with increase in atomic number across a given series is due to an increase in the nuclear charge with increase in the atomic number.
• The added electrons enter into the (n-1) d-subshell and shield the valence electrons from the nucleus.
• Thus, the effect of the increased nuclear charge is opposed by the screening effect of (n-1) d-electrons.
• This is why the increase in ionization enthalpy with increase in atomic number is slow, not very regular and reasonably constant.