Question

First IE of 5d-elements are higher than those of 3d and 4d-elements. This is due to
A) Lesser effective nuclear charge is experienced because of the weak shielding of the nucleus by 4f-electrons
B) Greater effective nuclear charge is experienced because of the weak shielding of the nucleus by 4f-electrons
C) Both (A) and (B)
D) None of the above

Answer 1

The ionization energy of an atom is the energy required to remove an electron from its outermost orbital. The factors such as shielding effect and effective nuclear charge play an important role in ionization energy. One can apply these concepts with the elements and relate them with the given options.

Complete step by step answer:

1. First of all we will learn about the concept of first ionization energy. The first ionization energy can be elaborated as the energy required to remove the first electron from the outermost orbit of an element.
2. Now we will discuss the factors which can affect the ionization energy of an element. The first factor is the shielding effect where the higher shielding effect will make it hard to remove the electron which will result in higher ionization energy.
3. Now in the case of 5d-elements there is a 4f-orbital present previous to 5d-orbital and it gets filled first. As we know the f orbitals show very poor shielding effect the 5d orbitals get close to the nucleus.
4. Now this makes the 5d orbital having more z effective which eventually makes the atomic radius of the element lower.
   Therefore, due to greater effective nuclear charge is experienced because of the weak shielding of the nucleus by 4f-electrons the first IE of 5d-elements are higher than those of 3d and 4d-elements which shows option B as the correct choice of answer.

Note: The greater effective nuclear charge in 5d-electrons is experienced because of the weak shielding of the nucleus by 4f-electrons which makes the size of elements lower and this phenomenon is called lanthanide contraction.