Question

1. which of the following substances would you expect to have a low melting point?

a. sodium chloride
b. silicon dioxide
c. carbon dioxide
d. aluminium chloride

Explanation:

• Sodium chloride (\(NaCl\)) is an ionic compound. Ionic compounds have high melting points due to the strong electrostatic forces (ionic bonds) between the positive and negative 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 intermolecular forces (van der Waals forces). Only a small amount of energy is needed to overcome these forces, so it has a low melting point.
• Aluminium chloride (\(AlCl_3\)) has a relatively complex bonding situation. In the solid - state, it has some ionic character, but it also has some covalent character. However, compared to simple molecular \(CO_2\), it has a higher melting point.

Answer:

C. carbon dioxide