Question

Higher values of ionization energies in 5d transition elements are consistent with the:
A.relative smaller effective nuclear charge
B.relatively smaller size of their atoms
C.relatively smaller penetration
D.all the above are correct

Answer 1

The minimum amount of energy required to remove the electron from the outermost shell of an isolated gaseous atom is known as ionization energy. The ionization energy depends upon the size (inversely proportional to size of an atom).

Complete step by step answer:
Ionization energy: The energy required to remove an electron from the outermost shell of an isolated gaseous atom is known as ionization energy. We can also describe the ionization energy as the measure of difficulty in removing an electron from an isolated gaseous atom or the ability to donate the outermost electron of an atom.
The electron filling affects the ionization energy. If the electrons are filled in poor shielding orbital then the nuclear attraction or we can say attraction between electrons and protons will increase and hence the ionization energy will increase, if the electrons are filed in the orbital having good shielding then the attraction between nucleus and electrons will decrease and at last the ionization energy for electron will decrease. So overall we can say that ionization energy depends on the size of the atom, if the atom is small the ionization energy is more and if the size is large, the ionization energy is less.
Here in the 5d transition elements, the electrons are filled in the next 4f orbital and due to poor shielding the nuclear attraction increases towards the electrons, which results in smaller size and higher ionization energy.
Therefore higher values of ionization energies in 5d transition elements are consistent with the relatively smaller size of their atoms.

So, option (B) is correct.

Note:
In Lanthanide the electron filling is done in 4f orbital continuously which is also a poor shielding orbital, so it can’t hold or we can say protect electrons from the nuclear attraction and the results in reduction of atomic size.