Molecular shape and VSPER

Question

H

I . .

H---------C ------C ====N --------H

I I

H H

Answer the following questions about the Lewis structure

of the compound given on the right.

A. What is the molecular shape at the leftmost carbon

atom in the compound? Explain your answer. (3)

shape at leftmost carbon: ______________________________________

B. What value would VSEPR theory predict for the C–N–H bond angle in the

compound? Explain your answer. (4)

C–N–H bond angle: _______________

Answer 1

In VSEPR, what matters are the number of bonds and lone pairs around each atom. The order of the bonds - single, double, triple - does not matter.

The leftmost carbon has 4 bonds and 0 lone pairs: all 4 'electron domains' seek positions as far apart as possible in 3 dimensional space. Therefore, the geometry will be tetrahedral.

The nitrogen has 1 single bond, 1 double bond, and 1 lone pair. We just say 2 bonds, 1 lone pair. All 3 'electron domains' repel each other, again, and seek positions as far apart as possible in space: geometry is trigonal planar. Bond angle therefore is 120 degrees.