Which statement generally describes covalent molecular substances compared with ionic compounds?

Which statement generally describes covalent molecular substances compared with ionic compounds?

• A. They often have lower melting points and do not conduct electricity as solids.
• B. They always conduct electricity as solids.
• C. They form giant lattices with metallic bonds.
• D. They are always soluble in water as electrolytes.

Answer: (A)

Covalent molecular substances are held together inside each molecule by strong covalent bonds, but the forces between molecules are much weaker van der Waals forces. That means less energy is needed to separate them, so they tend to have lower melting points than ionic compounds, which rely on strong electrostatic attractions in an extended lattice. Additionally, in the solid state these substances don’t have free ions or delocalized electrons to carry charge, so they don’t conduct electricity. This combination—weaker overall bonding between molecules and no freely moving charge carriers—explains why covalent molecular substances generally melt at lower temperatures and do not conduct electricity as solids. The other statements don’t fit this pattern: they don’t form giant metallic-like lattices, and being soluble or acting as electrolytes is not universally true for covalent molecular substances.

Covalent molecular substances are held together inside each molecule by strong covalent bonds, but the forces between molecules are much weaker van der Waals forces. That means less energy is needed to separate them, so they tend to have lower melting points than ionic compounds, which rely on strong electrostatic attractions in an extended lattice. Additionally, in the solid state these substances don’t have free ions or delocalized electrons to carry charge, so they don’t conduct electricity. This combination—weaker overall bonding between molecules and no freely moving charge carriers—explains why covalent molecular substances generally melt at lower temperatures and do not conduct electricity as solids. The other statements don’t fit this pattern: they don’t form giant metallic-like lattices, and being soluble or acting as electrolytes is not universally true for covalent molecular substances.