What is formal charge? How is formal charge calculated? How is it helpful?

Understanding the calculation of formal charges in chemistry is a fundamental skill, as it gives insight into the distribution of electrons within a molecule. To calculate the formal charge on an atom, you would employ the simple formula:
\[\begin{equation}\text{Formal Charge} = (\text{Valence electrons on free atom}) - (\text{Non-bonding electrons}) - \frac{1}{2}(\text{Bonding electrons})\end{equation}\]
Begin by identifying the number of valence electrons the atom would have in its unbound state—the number it naturally contains in its respective group on the periodic table. Then, count the non-bonding electrons, which are the electrons in the lone pairs around that atom. Finally, count the bonding electrons, which are those involved in bonds with other atoms, and divide this number by two because these electrons are shared between two atoms. Ensuring accuracy in these calculations is key to establishing the atoms' formal charges correctly and predicting the molecule's behavior.

The concept of the formal charge plays a pivotal role in understanding molecular architecture and reactivity. A zero or low formal charge in a molecule indicates that the atoms are close to their most stable configuration. Molecules tend to minimize formal charges across the entire structure to reach a state of greater stability. This principle aids chemists in predicting the most likely arrangement of atoms in a molecule.
Moreover, a formal charge can help foretell likely sites of chemical reactions. Atoms with positive formal charges can act as electrophiles, attracted to electron-rich areas, while atoms with negative formal charges can behave as nucleophiles, seeking out electron-poor regions—the essential players in many chemical processes.

Lewis structures are a visual representation that illustrate the bonding between atoms of a molecule and the lone pairs of electrons that may exist. The dots represent electrons, while lines signify the bonds between atoms. These diagrams provide immediate insight into the connectivity of atoms and can be used to calculate formal charges. Building an accurate Lewis structure involves determining how many electrons are available for bonding, how the atoms are connected, and if multiple bonds are necessary to satisfy the octet rule—where atoms strive to complete their valence shell with eight electrons.
Correct Lewis structures are not just a means of representation but a critical step in predicting molecular properties and reactivity, thus serving as an indispensable tool for chemists.

Molecular stability is influenced by several factors, including the distribution of charge and the fulfillment of the octet rule as shown in Lewis structures. When atoms achieve a formal charge close to zero, they are typically at their most stable. This is due to the arrangement of electrons that minimizes repulsion between electron pairs and maximizes attractions in the system.
Stable molecules are generally less reactive and have lower potential energy. Evaluating formal charges is thus not only a theoretical exercise but also a practical application that affects our understanding of chemical kinetics and potential energy surfaces, leading to more effective designs of chemical reactions and products.