Organic Chemistry

Formal Charge

Formal Charge: number of valence electrons for an atom - (number of lone pair electrons

+ number electrons in bonds/2)

FC=Nvalence−

(

Nlonepairs+Nelectrons 2

)

In chemistry, a formal charge (FC) on an atom in a molecule is defined as:

FC = number of valence electrons of the atom - ( number of lone pair electrons on this

atom + total number of electrons participating in covalent bonds with this atom / 2).

FC=Nvalence−

(

Nlonepairs+Nparticipatingelectrons 2

)

When determining the correct Lewis structure (or predominant resonance structure) for
a molecule, the structure is chosen such that the formal charge on each of the atoms is
minimized.

9.2.1 Examples

carbon in methane

FC= 4−

(

0+^82

)

= 0

Nitrogen inNO− 2

FC= 5−

(

2+^62

)

= 0

double bonded oxygen inNO 2 −

FC= 6−

(

4+^42

)

= 0

single bonded oxygen inNO− 2

FC= 6−

(

6+^22

)

=− 1

Figure 12 Methane (CH 4 ): black is carbon, white is hydrogen

Figure 13Nitrogen dioxide (NO 2 ): blue is nitrogen, red is oxygen