Numerical answer · +4 / −1
The number of lone pairs on the nitrogen atom in NH₃ is x.
Answer and solution
Answer 1
Solution
Chemistry ma’am · 4 steps
Five valence electrons on N, three spent on bonds: the two left over sit as one lone pair.
- Count valence electrons. Nitrogen is in group 15, so a nitrogen atom brings 5 valence electrons to the molecule.
- Spend electrons on bonds. Each N-H bond takes one electron from nitrogen. With three hydrogens, 3 of the 5 electrons are used up, leaving 5 - 3 = 2.
- Pair the leftovers. Unshared electrons are always counted in twos, so those 2 electrons make 2/2 = 1 lone pair.
- So. Nitrogen in NH₃ carries 3 bond pairs and 1 lone pair, giving x = 1.
The common slip. Reporting the leftover electrons instead of the pairs gives 2, but those two electrons are only one lone pair.
The idea to keep. A lone pair is the leftover valence electrons divided by two. Always count one electron per bond from the central atom, then pair up whatever is left.
Answer from the NTA final answer key. Solution by PrepWiser.