Question

which of the following substances would you expect to have a low melting point?
a. sodium chloride
b. silicon dioxide
c. carbon dioxide
d. aluminum chloride

Explanation:

• Sodium chloride (\(NaCl\)) is an ionic compound. Ionic compounds have relatively high melting points due to the strong electrostatic forces (ionic bonds) between the ions.
• Silicon dioxide (\(SiO_2\)) has a giant covalent (network covalent) structure. In a giant covalent structure, atoms are held together by a large number of strong covalent bonds. A large amount of energy is required to break these bonds, so it has a high melting point.
• Carbon dioxide (\(CO_2\)) is a simple molecular compound. In simple molecular compounds, the molecules are held together by weak van der Waals forces (inter - molecular forces). Only a small amount of energy is needed to overcome these weak forces, so it has a low melting point.
• Aluminum chloride (\(AlCl_3\)) has a more complex bonding situation. In the solid state, it has some covalent character in its bonding, but it is not a simple molecular solid like \(CO_2\) in terms of having extremely weak inter - particle forces for melting.

Answer:

C. carbon dioxide