Question

There are four constitutional isomers with the molecular formula C₃H₉N. Draw a Lewis structure for each isomer and determine the number of lone pairs on the nitrogen atom in each case.

Answer 1

Solution

The task is to draw Lewis structures for all constitutional isomers with the molecular formula  C₃H₉N and to determine the number of lone pairs on nitrogen in each. Constitutional isomers are compounds with the identical molecular formula, but with different connectivity of atoms.

When drawing Lewis structures, first determine the number of valence electrons for each atom. The number of valence electrons is indicated by the group number. Hence, carbon has 4, hydrogen 1, and nitrogen 5 valence electrons.

Then, connect atoms that can form more than one bond. There are four different ways to connect three carbons and nitrogen and these are the skeletons of the isomers.

Then add hydrogens following the octet rule. The rule states that each atom tends to have 8 electrons in its valence shell (except hydrogen which tends to have a duet) in order to have a noble gas configuration and hence maximum stability.

Wherever you see an unpaired electron, add hydrogen.

By the distribution of hydrogens, we get four constitutional isomers with the formula  C₃H₉N.

A lone electron pair is present on an atom but is not shared with other atoms. As indicated with blue color, the nitrogen atom in each structure has one lone electron pair.