Question

first ionization enthalpy of 5D elements are higher than those of 3D and 4D elements why

Answer 1

Heya dear!!!


Here is your answer,

Well the main reason behind this is,

=> Poor Shielding Effect

Well for example let's see the elements of 3d, 4d and 5d series.

3d = Mn, 4d = Tc and 5d = Re.

Mn = (Ar) 4s2 3d5
Tc = (Kr) 4d6 5s1
Re = (Xe) 4f14 5d5 6s2

Now,
As we can see that in Re ie 5d series has a 4f orbital as well which is not pr sent in 3d and 4d. Now as we know that 'f' orbitals have poor shielding as compared to 'd' orbital and as we know that poor shielding results in the increase in the attraction of the outermost electrons and the nucleus, thus more energy will be required to remove the outermost electron from 'f' orbital as compared to 'd' orbital thus the first ionisation energy of 5d orbitals are higher than 3d and 4d orbitals.



Hope it helps you,
Thank you.

Answer 2

1st ionisation energies of 5d elements are higher than those of 3d or 4d elements this is due to the greater effective nuclear charge acting on outer valence electrons because of weak shielding by 4f electrons.