CHEMISTRY · Single correct · AP · Chemistry · Compound Structure and Properties · Compound Structure and Properties
Problem
Solid sodium metal conducts electricity, whereas crystalline sodium chloride does not. Which of the following explanations best distinguishes the two solids in terms of charge-carrier mobility?
(a) Sodium metal contains mobile Na+ ions that can drift through the lattice, whereas in NaCl the strong ionic bonds prevent the ions from moving.
(b) In NaCl, electrons are delocalized but occupy lower-energy orbitals that keep them localized, while in sodium metal the same electrons reside in higher-energy bands that allow them to move.
(c) In sodium metal, valence electrons are delocalized and free to move throughout the lattice of fixed Na+ cores, but in crystalline NaCl the Na+ and Cl− ions are locked in place and no electrons are free to migrate.
(d) NaCl is composed of neutral molecular units held together only by intermolecular forces, so there are no charged particles to carry current, whereas sodium metal forms a continuous lattice that permits charge flow.