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If two nonmetals both want to gain electrons to fill their outer shells, how can they bond without either one losing electrons?
Instead of transferring electrons like in ionic bonding, atoms overlap their valence orbitals to share electron pairs in a covalent bond.
In 1916, American chemist Gilbert N. Lewis proposed that atoms are most stable when surrounded by eight valence electrons, a guideline known as the octet rule.
How do we systematically build a valid Lewis structure from a chemical formula every single time?

The 5-Step Lewis Blueprint

Drawing Lewis structures follows a strict bookkeeping method that ensures every valence electron is accounted for.
Hydrogen is an exception that follows the duet rule, needing only 2 electrons to fill its 1s1s orbital, so it never takes lone pairs or multiple bonds.
What happens when multiple valid Lewis arrangements are possible for the same formula?

Formal Charge

Formal charge is a bookkeeping tool that tracks whether an individual atom in a molecule owns more or fewer valence electrons than it does in its free elemental state.
To find formal charge (FCFC), subtract nonbonding electrons (NN) and half of the bonding electrons (BB) from the atom's free valence electron count (VV): FC=V−N−B2FC = V - N - \frac{B}{2}