Chemistry Chemical Bonding ETEA 2024
PMDC Verified Question 9 of 102
Which one of the following molecules has a pyramidal structure?
A
\( \text{C}_2\text{H}_4 \)
B
\( \text{CH}_4 \)
C
\( \text{H}_2\text{O} \)
D
\( \text{NH}_3 \)
Tap any option to test your recall and reveal the step-by-step Propolis autopsy.

Propolis Cognitive Error Autopsy

Official Correct Choice:
Option D: \( \text{NH}_3 \)
Concept:

A pyramidal (specifically trigonal pyramidal) molecular geometry occurs when an \( \text{sp}^3 \) hybridized central atom possesses exactly 3 bond pairs and 1 lone pair.

Formula:

$$ \text{Type} = \text{AB}_3\text{E} $$

Solution:

  • Ammonia (\( \text{NH}_3 \)) has a central Nitrogen atom bonded to 3 Hydrogens.


  • Nitrogen has 1 lone pair remaining.


  • This lone pair forces the three N-H bonds downward into a 3D pyramid shape to minimize repulsion.


Why other options are incorrect:

  • Option A: Ethene is flat/planar (\( \text{sp}^2 \)).
  • Option B: Methane is a perfect tetrahedron (4 bonds, 0 lone pairs).
  • Option C: Water is bent/angular (2 bonds, 2 lone pairs).

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