Explain the meaning of the following terms. (a) expanded octet (b) resonance (c) unshared electron pair (d) odd-electron species

Question: Define and provide an example for each of the following terms: (a) expanded octet, (b) resonance, (c) unshared electron pair, and (d) odd-electron species. Answer: (a) Expanded octet refers to an atom having more than the usual eight electrons in its valence shell, as seen in sulfur hexafluoride (SF6) with sulfur surrounded by 12 valence electrons. (b) Resonance occurs when a molecule's actual structure is a hybrid of two or more contributing Lewis structures, like ozone (O3), displaying bonds of intermediate length and strength. (c) An unshared electron pair, also known as a lone pair or nonbonding electron pair, is localized on a single atom, such as the nitrogen atom in ammonia (NH3). (d) An odd-electron species, or a free radical, is a molecule or ion containing an unpaired electron in its atomic or molecular orbitals, making it highly reactive, like nitric oxide (NO) with an unpaired electron in its molecular orbital.