# The shape of ammonia molecule is?

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## The shape of ammonia molecule is?

A. Trigonal planar

B. Octahedral

C. Square planar

D. Tetrahedral

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.

The shape of ammonia, which has one nitrogen and three hydrogen atoms could be trigonal to begin with, but be careful, Ammonia is either trigonal pyramidal, or tetrahedral. Ammonia is never a flat trigonal planar molecule.

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:

1. Option A is incorrect. never trigonal planar, but trigonal pyramidal.
2. Option B is incorrect. never octahedral. Oct, means 8, and could not possibly be the answer.
3. C is incorrect. not square planar.
4. D is the correct answer. yes, either trigonal pyramidal or tetrahedral.

## KEY-POINTS…

• 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 /

Feel free to ask us questions on this topic, we will respond in minutes…

Give three examples of molecules with tetrahedral shapes

Methane, CH4 is one of them…

Others are CCL4, SiH4, ammonuim ion NH4+, and MnO4 ion…

Give two examples of molecules whose geometry is trigonal pyramidal

Trigonal pyramidal = NH3, PCL3, & H3O+…

Ammonia is both trigonal pyramidal and tetrahedral…

Ammonia is both trigonal pyramidal and distorted-tetrahedral.. . depending on what you are looking at. Don’t worry when you get to advanced chemistry, you would understand better. but for now, you should always choose tetrahedral for ammonia especially when trigonal pyramidal isn’t part of the options. Sometimes the options might include trigonal planar or trigonal bipyramidal, both of which are wrong.