Identify the molecule / ion in which the ratio of $\sigma$ to $\pi$ bonds is 3:2

Question

Which of the following elements has the highest electronegativity?

Answer 1

To determine which molecule or ion has a sigma (σ) to pi (π) bond ratio of 3:2, we need to analyze the bonding structure of each option provided.

Given Options:

Solution:

HCO₃⁻ (Bicarbonate Ion):
- It has one carbon atom bonded to three oxygen atoms.
- There can be resonance among the oxygen positions. Typically, it has 2 σ and 1 π bond distributed as C=O (1 π bond) and C-O (2 σ bonds).
- Thus, the ratio of σ to π bonds is 2:1.
CH₂(CN)₂ (Malononitrile):
- This molecule has two cyanide groups (CN) attached to a central methylene (CH₂) group.
- Each CN group contains 1 σ bond (C-N) and 2 π bonds (as N≡C has 2 π bonds: 1 in N=C and another C=C).
- In total: 2 σ bonds from 2 C-N, 4 π bonds from two N≡C (2 π each) and 2 σ bonds from CH₂.
- The total bonds are 4 σ, 4 π from (C ≡ N) and 1 π bond from C=N (after redistribution from resonance).
- The ratio of σ to π bonds becomes 3:2 for equally distributed resonance forms.
HClO₄ (Perchloric Acid):
- In HClO₄, Cl is bonded to four oxygen atoms.
- There is 1 π bond in the double-bonded oxygen, and 4 σ bonds (Cl-O, 3 single bonds and 1 double bond).
- The ratio is 4:1.
XeO₃ (Xenon Trioxide):
- In this compound, xenon (Xe) forms three Xe-O bonds.
- It includes 3 σ bonds and 3 π bonds based on regular Lewis structure configuration for each double-bonded oxygen.
- However, normally still not balancing a 3:2 ratio across all resonance structures possible without special adjustment.

Conclusion: The molecule CH₂(CN)₂, malononitrile, has a total σ to π bond ratio of 3:2, making it the correct choice for the given problem.

Answer 2

To determine which molecule or ion has a sigma (σ) to pi (π) bond ratio of 3:2, we need to analyze the bonding structure of each option provided.

Given Options:

Solution:

HCO₃⁻ (Bicarbonate Ion):
- It has one carbon atom bonded to three oxygen atoms.
- There can be resonance among the oxygen positions. Typically, it has 2 σ and 1 π bond distributed as C=O (1 π bond) and C-O (2 σ bonds).
- Thus, the ratio of σ to π bonds is 2:1.
CH₂(CN)₂ (Malononitrile):
- This molecule has two cyanide groups (CN) attached to a central methylene (CH₂) group.
- Each CN group contains 1 σ bond (C-N) and 2 π bonds (as N≡C has 2 π bonds: 1 in N=C and another C=C).
- In total: 2 σ bonds from 2 C-N, 4 π bonds from two N≡C (2 π each) and 2 σ bonds from CH₂.
- The total bonds are 4 σ, 4 π from (C ≡ N) and 1 π bond from C=N (after redistribution from resonance).
- The ratio of σ to π bonds becomes 3:2 for equally distributed resonance forms.
HClO₄ (Perchloric Acid):
- In HClO₄, Cl is bonded to four oxygen atoms.
- There is 1 π bond in the double-bonded oxygen, and 4 σ bonds (Cl-O, 3 single bonds and 1 double bond).
- The ratio is 4:1.
XeO₃ (Xenon Trioxide):
- In this compound, xenon (Xe) forms three Xe-O bonds.
- It includes 3 σ bonds and 3 π bonds based on regular Lewis structure configuration for each double-bonded oxygen.
- However, normally still not balancing a 3:2 ratio across all resonance structures possible without special adjustment.

Conclusion: The molecule CH₂(CN)₂, malononitrile, has a total σ to π bond ratio of 3:2, making it the correct choice for the given problem.

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