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Chemical Bonding and Molecular Structure question

2024 · 31 Jan · Shift 1 · Q13
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Chemical Bonding and Molecular Structure question

2024 · 31 Jan · Shift 1 · Q13

JEE MainChemistryChemical Bonding and Molecular StructureMCQ+4 / −1
The linear combination of atomic orbitals to form molecular orbitals takes place only when the combining atomic orbitals A. have the same energy B. have the minimum overlap C. have same symmetry about the molecular axis D. have different symmetry about the molecular axis Choose the most appropriate from the options given below:
  1. A
    B, C, D only
  2. B
    A, B, C only
  3. C
    B and D only
  4. D
    A and C only
View written solutionFree

Correct answer: D

  1. Condition for LCAO to occur

For atomic orbitals to combine and form molecular orbitals effectively, the following standard conditions must be satisfied:

  • Comparable / same energy of combining atomic orbitals
  • Same symmetry about the molecular axis
  • Appreciable (maximum) overlap, not minimum overlap

So let us check each statement.


  1. Evaluate statement A: "have the same energy"

This is essentially correct in MO theory.

Atomic orbitals combine effectively when their energies are equal or nearly equal. Hence this is taken as a valid condition.

So, A is correct.


  1. Evaluate statement B: "have the minimum overlap"

This is incorrect.

For molecular orbital formation, overlap must be appreciable / maximum, because greater overlap gives stronger interaction and better MO formation.

So, B is incorrect.


  1. Evaluate statement C: "have same symmetry about the molecular axis"

This is correct.

Only orbitals with the same symmetry relative to the internuclear axis can combine.

Example: two sss orbitals can combine; an sss orbital and a properly oriented pzp_zpz​ orbital can combine; but orbitals of incompatible symmetry cannot.

So, C is correct.


  1. Evaluate statement D: "have different symmetry about the molecular axis"

This is the opposite of the required condition.

Orbitals with different symmetry do not combine effectively.

So, D is incorrect.


  1. Select the correct option

Correct statements are:

A and CA \text{ and } CA and C

From the given options, this corresponds to Option D.


  1. Comparison with stored answer

Stored correct answer = D

Derived answer = D

They match.

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