Question

Which of the following statement is not correct about the periodic classification of elements?

• A. The properties of the elements are the periodic functions of their atomic numbers.
• B. Non-metallic elements are lesser in number the metallic elements.
• C. The first ionization energies of the elements along a period do not vary in a regular manner with increase in atomic number.
• D. For transition elements the d-sub shells are filled with electrons monotonically with increase in atomic number.

Answer 1

The correct option is D

For transition elements the d-sub shells are filled with electrons monotonically with increase in atomic number.

The electronic configuration of $Cr$ (atomic number -24) is $\left[Ar\right]3d^{5}4s^1$. Here in this case the d-orbitals is half filled because fully filled and half filled orbitals are more stable due to the symmetric distribution and exchange of energy. There are other examples such as Mo (atomic number - 42) $\left[Kr\right]4d^{5}5s^1$. From this we can infer that d-subshells are not filled with electrons monotonically with increase in atomic number.

The other statements which are true regarding periodic classification of elements are:

(i) The properties of the elements are the periodic functions of their atomic numbers.

(ii) Non-metallic elements are lesser in number the metallic elements.

(iii) The first ionization energies of the elements along a period do not vary in a regular manner with increase in atomic number.