The shape of ammonia molecule is?
A. Trigonal planar
B. Octahedral
C. Square planar
D. Tetrahedral
QUICK ANSWER…
D
DETAILS…
The shape of ammonia molecule is either trigonal pyramidal or distorted tetrahedral…
Questions like this are a reason why you can’t score 400/400 in JAMB. This is because over 90% of the intelligent ones will choose option A. There’s a big difference between trigonal pyramidal, and trigonal planar.
Let me explain why ammonia could either be trigonal pyramidal or tetrahedral and never trigonal planar.
Atomic number of nitrogen = 7
Atomic number of hydrogen = 1
Electronic configuration of nitrogen = 2, 5
This implies that for a bond to form, 1 nitrogen atom combines with 3 hydrogen atoms to form a molecule like this:
Now, if we consider only the hydrogen atoms without the lone pair of electrons at the top, the shape will be trigonal pyramidal with each hydrogen making a bond angle of 107° with themselves.
But if we also consider the lone pair of electrons at the top of the sketch, the shape becomes tetrahedral.
Now for the right answer to the above question:
- Option A is incorrect. never trigonal planar, but trigonal pyramidal.
- Option B is incorrect. never octahedral. Oct, means 8, and could not possibly be the answer.
- C is incorrect. not square planar.
- D is the correct answer. yes, either trigonal pyramidal or tetrahedral.
KEY-POINTS…
You may please note these/this:
- Please note the difference between trigonal pyramidal and trigonal planar.
- In trigonal pyramidal, combining atoms are arranged in the form of a three-dimensional pyramid with nitrogen at the top, and three hydrogens forming the base.
- In trigonal planar, we are basically looking at a structure in two-dimensional plane, this is not the case for ammonia, as it’s hydrogens actually spreads into three dimension with each hydrogen making a bond angle of 107° with each other.
- Ammonia is either trigonal pyramidal or tetrahedral, depending on what you are considering.
- Trigonal planar = wrong!
- Trigonal bipyramidal = wrong!
- Trigonal pyramidal = correct!
- Distorted tetrahedral = correct!
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/ culled from 2020 JAMB-UTME chemistry past question 20 /
