Diamond is an electrical insulator and extremely hard
CHEMISTRY · Single correct · AP · Chemistry · Properties of Substances and Mixtures · Properties of Substances and Mixtures
Problem
Diamond is an electrical insulator and extremely hard, whereas graphite is soft and conducts electricity parallel to its layers, even though both are composed only of carbon atoms. Which statement best accounts for these contrasting properties?
(a) Diamond is an ionic lattice of C4− and C4+ ions, whereas graphite behaves like a metallic solid with mobile electrons throughout the crystal.
(b) Diamond consists of discrete Cn molecules held together only by London dispersion forces, while graphite is covalently bonded throughout the solid.
(c) Diamond features a three-dimensional network of sp3 C–C σ bonds that lock atoms rigidly in place and leave no mobile electrons, whereas graphite consists of two-dimensional sheets of sp2 carbon atoms with delocalized π electrons that enable conductivity and allow the sheets to slide.
(d) Both diamond and graphite contain sp3-hybridized carbon atoms; diamond is hard because its layers are tightly packed, while graphite is soft because its layers are held together only by London dispersion forces, and its conductivity comes from the movement of σ electrons between layers.