Explain how covalent bonds form through electron sharing between nonmetals, apply the octet rule, and draw Lewis structures for simple molecules.
When two nonmetal atoms bond, neither one is willing to simply give up an electron -- both attract electrons too strongly (high electronegativity). Instead, they share one or more pairs of electrons, and that shared pair, attracted to both nuclei at once, is a covalent bond. Sharing lets both atoms count the shared electrons toward their own outer level, which is how both atoms can reach a stable, full outer level at the same time.
Most atoms aim for eight valence electrons total (counting shared pairs) to match the stable configuration of a noble gas -- this goal is called the octet rule. Hydrogen is the standard exception, aiming for just two electrons (a duet), since its only energy level holds a maximum of two.
A single bond shares one pair of electrons (two total). A double bond shares two pairs (four total), and a triple bond shares three pairs (six total) -- more shared pairs mean a shorter, stronger bond. In a Lewis structure, bonding pairs are drawn as lines (or dot pairs) between atoms, and any leftover valence electrons that are not being shared are drawn as lone pairs directly on their atom.
Mastery looks like: They correctly draw or describe Lewis structures for simple molecules, correctly counting bonding and lone pairs to confirm each atom satisfies its octet (or duet for hydrogen).
Common stumbles: Forgetting to include lone pairs when counting total electrons around an atom; assuming every atom needs exactly 8 electrons, including hydrogen.