Chemistry
Chemistry
Problem
Sodium chloride (NaCl) melts at 801 °C, whereas solid sucrose (C12H22O11) decomposes near 185 °C. Which of the following statements best explains the much higher melting point of NaCl? a) NaCl has a much higher molar mass than sucrose, so more thermal energy is needed to melt it. b) NaCl forms a giant covalent network, requiring the breaking of strong covalent bonds to melt, whereas sucrose is molecular. c) NaCl consists of oppositely charged ions held together by strong Coulombic attractions in a three-dimensional lattice, whereas sucrose molecules are held together only by hydrogen bonding and other weak intermolecular forces. d) NaCl experiences stronger London dispersion forces because its ions are larger and more polarizable than sucrose molecules.Intuitive explanation
NaCl is an ionic compound held together by strong electrostatic attractions between oppositely charged ions, while sucrose is a molecular compound bound by weaker intermolecular forces (hydrogen bonds). The key insight is that melting requires breaking the primary forces holding the solid together—ionic bonds are far stronger than hydrogen bonds, so NaCl needs much more thermal energy to melt. Sucrose decomposes at lower temperature because its weaker intermolecular forces break apart long before the covalent bonds within the molecule itself are disrupted.
Intuitive explanation
NaCl is an ionic compound held together by strong electrostatic attractions between oppositely charged ions, while sucrose is a molecular compound bound by weaker intermolecular forces (hydrogen bonds). The key insight is that melting requires breaking the primary forces holding the solid together—ionic bonds are far stronger than hydrogen bonds, so NaCl needs much more thermal energy to melt. Sucrose decomposes at lower temperature because its weaker intermolecular forces break apart long before the covalent bonds within the molecule itself are disrupted.