Formal charge is the charge assigned to an atom in a molecule, assuming that electrons in all chemical bonds are shared equally between atoms, regardless of relative electronegativity.
Knowing the formal charge on a particular atom in a structure is an important part of keeping track of the electrons and is important for establishing and predicting the reactivity.
Formula to calculate formal charge.
- V is the no. of valence electrons.
- N is the no. of non bonding valence electrons.
- B is the total number of electrons shared in bonds
Calculate the formal charge of Ammonia (NH3).
- It has 5 valence electrons.
- 2 non bonding valence electrons.
- 6 electrons shared in a bond.
- 1 valence electron.
- 0 non bonding valence electron.
- 2 electrons shared in a bond
Therefore, the result shows that the formal charge of ammonia is zero. This means that ammonia is a molecule.