AP CHEM VOCAB

Resonance hybrid

A molecule that cannot be represented by a single Lewis structure; the true structure is a blend of multiple resonance forms.

Delocalized electrons

Electrons that are shared across more than two atoms, not localized in a single bond or lone pair.

Coordinate covalent bond (dative bond)

A bond in which one atom donates both electrons for the shared pair. Example: NH₃ → BF₃ adduct.

Lone pair electrons

Pairs of valence electrons not involved in bonding, sitting on a single atom.

Free radical

A species with an unpaired electron, making it highly reactive. Example: •OH.

Bond dissociation energy (BDE)

Energy required to break a bond homolytically, splitting electrons equally between atoms.

Lattice energy

Energy released when 1 mole of an ionic solid forms from its gaseous ions; higher lattice energy means stronger ionic bonds.

Formal charge

Hypothetical charge on an atom assuming electrons in bonds are shared equally. Formula: FC = Valence electrons − (Lone pair electrons + ½ Bonding electrons).

Oxidation state

A measure of an atom's electron loss or gain in a compound, used in redox reactions.

Coordination complex

A central metal atom/ion bonded to ligands (molecules or ions that donate electron pairs).

Dipole moment

Measure of the separation of positive and negative charge in a molecule; indicates polarity.

Hybridized orbital

Orbital formed by mixing atomic orbitals on the same atom to form new, equivalent orbitals (e.g., sp³, sp²).

Atomic orbital

Region around a nucleus where an electron is likely to be found (s, p, d, f).

Molecular orbital (MO)

Orbital formed by overlap of atomic orbitals from two or more atoms; electrons belong to the whole molecule.

Bonding orbital

Molecular orbital lower in energy than the original atomic orbitals, stabilizing the molecule.

Antibonding orbital

Molecular orbital higher in energy than the original atomic orbitals, destabilizing the molecule (denoted with *).

Alloy

Mixture of two or more elements, at least one metal, with metallic properties.

Interstitial alloy

Smaller atoms fit into the gaps between larger metal atoms. Example: steel (C in Fe).

Substitutional alloy

Atoms of similar size replace metal atoms in the lattice. Example: brass (Zn replaces Cu).