Chapter 2: Q36E_a (page 59)

Assign formal charges to the atoms in each of the following molecules:

Short Answer

Expert verified

Answer

The formal charge on all H in is 0

The formal charge on C in is 0

The formal charge on O is -1

The formal charge on N is +1

Step by step solution

Formal charge

The formal charge is the electric charge present on an atom in a molecule. It indicates magnitude and charge, positive or negative.

Calculation of formal charge

The formal charge on an atom is equal to the number of valence electrons in a neutral and isolated atom minus the number of electrons present in its bonded atom form in a molecule. The number of electrons in a bonded atom is calculated as half the number of bonding electrons plus the nonbonding, that is, lone-pair electrons.

$F o r m a l C h a r g e = (N u m b e r o f v a l e n c e e l e c t r o n s i n f r e e a t o m) - (N u m b e r o f v a l e n c e e l e c t r o n s i n b o n d e d a t o m) = (N u m b e r o f v a l e n c e e l e c t r o n s i n f r e e a t o m) - (\frac{N u m b e r o f b o n d i n g e l e c t r o n}{2} + N u m b e r o f n o n b o n d i n g e l e c t r o n)$

Calculation of formal charge on all H in CH3

Using the above formula:

$F o r m a l c h a r g e = (N u m b e r o f v a l e n c e e l e c t r o n i n f r e e a t o m) - (\frac{N u m b e r o f b o n d i n g e l e c t r o n}{2} + N u m b e r o f n o n b o n d i n g e l e c t r o n) = 1 - (\frac{2}{2} + 0) = 1 - 1 = 0$

Calculation of formal charge on N

Using the above formula:

$F o r m a l c h a r g e = (N u m b e r o f v a l e n c e e l e c t r o n i n f r e e a t o m) - (\frac{N u m b e r o f b o n d i n g e l e c t r o n}{2} + N u m b e r o f n o n b o n d i n g e l e c t r o n) = 5 - (\frac{8}{2} + 0) = 5 - 4 = 1$

Calculation of formal charge on O

Using the above formula:

Calculation of formal charge on all C in CH3

Using the above formula:

$F o r m a l c h a r g e = (N u m b e r o f v a l e n c e e l e c t r o n i n f r e e a t o m) - (\frac{N u m b e r o f b o n d i n g e l e c t r o n}{2} + N u m b e r o f n o n b o n d i n g e l e c t r o n) = 4 - (\frac{8}{2} + 0) = 4 - 4 = 0$