JEE MainChemistryClassification of Elements and Periodicity in Properties
First ionisation enthalpy values of four consecutive period 2 elements (C, N, O, F) are given below. Choose the correct value for the element whose homonuclear diatomic molecule is paramagnetic in nature :
Options
- A1314 ~kJ ~mol ⁻¹
- B1402 ~kJ ~mol ⁻¹
- C1681 ~kJ ~mol ⁻¹
- D1086 ~kJ ~mol ⁻¹
Correct answer
A. 1314 ~kJ ~mol ⁻¹
Step-by-step solution
The four consecutive period 2 elements given are C, N, O, and F. According to Molecular Orbital Theory, among their homonuclear diatomic molecules ( C ₂ , N ₂ , O ₂ , F ₂ ), only O ₂ contains unpaired electrons in its anti-bonding ^ * molecular orbitals, making it paramagnetic. The first ionisation enthalpy generally increases across a period. However, Nitrogen has a stable half-filled 2p subshell ( 2s^2 2p^3 ), which makes its first ionisation enthalpy higher than that of Oxygen. The correct order of first ionisat