Formal charge is a concept used in chemistry to assess the distribution of electrons in a molecule or ion and evaluate the relative stability of different resonance structures. It provides a method to determine the electronic charge of individual atoms within a molecule, taking into account the shared and unshared electrons.

The formal charge of an atom in a molecule or ion is calculated by comparing the number of valence electrons it would have in an isolated state (based on its position in the periodic table) with the number of valence electrons it actually possesses in the molecule. The formula for calculating formal charge is:

Formal Charge = Valence Electrons - (Non-bonding Electrons + 0.5 * Bonding Electrons)

In a neutral molecule, the sum of formal charges for all atoms should be zero. In an ion, the sum of formal charges should equal the overall charge of the ion. Formal charges allow us to assess the distribution of electrons, identify potential sites of electron deficiency or excess, and determine the stability of different resonance structures within a molecule.

Formal charge helps in understanding and predicting the reactivity and chemical behavior of molecules. It assists in determining the preferred resonance structures and provides insights into the electron distribution and charge localization within a molecule. It is important to note that formal charges are not actual charges on atoms but rather a tool used to analyze electron distribution.