**Formal Charge Uses, Formula, and Examples**

Formal Charge Uses, Formula, and Examples

__Formal Charge:__** ****A formal charge (FC) is the charge assigned to an atom in a molecule. ** The formal charge (F.C.) is the charge assigned to an atom in a molecule, assuming that the electrons in all chemical bonds are shared equally between atoms.

When determining the best Lewis Structure (or predominant resonance) for a molecule, the structure is chosen such that the formal charge on each of the atoms is as close to zero as possible.

In order to calculate a formal charge, electrons are assigned to individual atoms within the molecule based on two different rules: bonding electrons must be divided equally across the different bonded atoms, and non-bonding electrons are considered part of the atom they are located.

**Formula to calculate Formal Charge:**

**FC = VE – NE – ½ BE**

**VE**** → **Valence Electrons

**NE**** → **Non-Bonding Electrons

**BE**** → **Bonding Electrons

**Uses of Formal Charge:**

1. The formal charge being a theoretical charge doesn’t indicate any real charge separation in the molecule.

2. Formal charges help in the selection of the lowest energy structure from a number of possible Lewis structures for a given species.

3. Knowledge of the lowest energy structure helps in predicting the major product of a reaction and also describes a lot of phenomena.

4. Generally, the lowest energy structure is the one with the smallest formal charges on the atoms and the most distributed charge.

**Examples to Calculate Formal charge:**

**1. Formal Charge on N in NO _{3}^{–} :**

Valence Electrons of N = 5, Non-Bonding Electrons of N = 0

Bonding Electrons of N = 10

According to formula FC on N = 5 – 0 – ½ × 10 = 0

**2. Formal charge on each oxygen in O _{3} Molecule:**

**3. Formal charge on Cl atom of HClO _{4}:**

FC = 7 – 0 **– **½ × 14 = 0

**4. The formal charge on Carbon and oxygen of HCHO:**

FC = VE – NE – 1/2 BE

Formal Charge Uses, Formula, and Examples

## 1 Comment

Interesting lesson