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NEET CHEMISTRYOrganic Chemistry – Some Basic Principles and Techniques Easy

Question

A molecule/ion among the following species that does not exist under normal conditions is:

A

Be₂⁺

B

Be₂

C

B₂

D

Li₂

Step-by-Step Solution

  1. Criterion for Existence: According to Molecular Orbital Theory (MOT), a molecule is viable only if its Bond Order is positive (greater than zero).
  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 bonding electrons and NaN_a is the number of antibonding electrons.
  3. Analyze Be₂:
  • Beryllium (Be, Z=4) has 4 electrons. The molecule Be2Be_2 has a total of 8 electrons.
  • Configuration: σ1s2σ1s∗2σ2s2σ2s∗2\sigma_{1s}^2 \sigma_{1s}^{*2} \sigma_{2s}^2 \sigma_{2s}^{*2}.
  • Nb=4N_b = 4 (22 in σ1s\sigma_{1s}, 22 in σ2s\sigma_{2s}).
  • Na=4N_a = 4 (22 in σ1s∗\sigma_{1s}^*, 22 in σ2s∗\sigma_{2s}^*).
  • Calculation: Bond Order=12(4−4)=0\text{Bond Order} = \frac{1}{2}(4 - 4) = 0.
  1. Conclusion: A bond order of zero implies no net bond forms between the atoms. Therefore, Be2Be_2 does not 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 moleculeionfollowingspeciesnormalconditions

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