Chemistry Chemical Bonding MDCAT 2018
PMDC Verified Question 87 of 102
Which if the following molecule has largest number of shared pair electrons?
A
\( \text{NH}_3 \)
B
\( \text{CO}_2 \)
C
\( \text{C}_2\text{H}_4 \)
D
\( \text{N}_2 \)
Tap any option to test your recall and reveal the step-by-step Propolis autopsy.

Propolis Cognitive Error Autopsy

Official Correct Choice:
Option C: \( \text{C}_2\text{H}_4 \)
Concept:

The number of shared electron pairs equals the total number of covalent bonds (both sigma and pi) in the molecule.

Formula:

$$ \text{Shared Pairs} = \text{Total Bonds} $$

Solution:

  • \( \text{NH}_3 \): 3 single bonds = 3 shared pairs.


  • \( \text{CO}_2 \) (\( \text{O=C=O} \)): 2 double bonds = 4 shared pairs.


  • \( \text{N}_2 \) (\( \text{N} \equiv \text{N} \)): 1 triple bond = 3 shared pairs.


  • \( \text{C}_2\text{H}_4 \) (Ethene): 4 C-H single bonds + 1 C=C double bond = 6 covalent bonds = 6 shared pairs.


Why other options are incorrect:

  • Option A, Option B, Option D: These molecules possess fewer total bonds, hence fewer shared pairs compared to ethene.

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