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NEET CHEMISTRYOrganic Chemistry – Some Basic Principles and Techniques Easy

Question

A molecule that cannot exist is:

A

Li₂

B

C₂

C

O₂

D

He₂

Step-by-Step Solution

  1. Principle: According to Molecular Orbital Theory (MOT), a molecule is stable and can exist only if its Bond Order is positive (non-zero). If the bond order is zero, the attractive and repulsive forces cancel out, and no bond is formed.
  2. Bond Order Formula: Bond Order=12(Nb−Na)\text{Bond Order} = \frac{1}{2}(N_b - N_a), where NbN_b is the number of electrons in bonding orbitals and NaN_a is the number of electrons in anti-bonding orbitals.
  3. Analyze He₂:
  • Helium (Z=2Z=2) has electronic configuration 1s21s^2.
  • The molecule He2He_2 would have 2+2=42 + 2 = 4 electrons.
  • MOT Configuration: σ1s2σ1s∗2\sigma_{1s}^2 \sigma^*_{1s}{}^2.
  • Nb=2N_b = 2, Na=2N_a = 2.
  • Bond Order = 12(2−2)=0\frac{1}{2}(2 - 2) = 0.
  1. Conclusion: Since the bond order is zero, He2He_2 is unstable and cannot exist.

Exam Context & Concepts Covered

This question aligns with the NEET CHEMISTRY syllabus, specifically targeting concepts from Organic Chemistry – Some Basic Principles and Techniques . Mastering this topic is crucial for scoring well in the upcoming medical entrance examinations. Solving conceptually related problems will help you understand the nuances of these concepts and improve your problem-solving speed.

CHEMISTRYOrganic Chemistry – Some Basic Principles and Techniques moleculecannot

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