Which statement pairs a property of ionic compounds with a property of covalent molecules?

Which statement pairs a property of ionic compounds with a property of covalent molecules?

• A. Ionic compounds have high melting points and conduct electricity when molten or dissolved; covalent molecules often have lower melting points and do not conduct electricity in water.
• B. Ionic compounds are always liquids; covalent molecules always gaseous.
• C. Ionic compounds conduct electricity as solids; covalent molecules conduct electricity in solid state.
• D. Ionic compounds have low melting points; covalent molecules have high melting points.

Answer: (A)

The main idea here is how bonding affects melting point and electrical conductivity. Ionic compounds form a strong lattice of oppositely charged ions, which takes a lot of energy to break, giving them high melting points. When they are molten or dissolved, the ions are free to move, so they conduct electricity. Covalent molecules are discrete units held together by covalent bonds, with much weaker forces between molecules, so their melting points are usually lower. In water, covalent molecules don’t typically form ions, so they don’t conduct electricity. This makes the statement that pairs a property of ionic compounds with a property of covalent molecules the best fit: ionic compounds have high melting points and conduct electricity when molten or dissolved, while covalent molecules tend to have lower melting points and do not conduct electricity in water.

The main idea here is how bonding affects melting point and electrical conductivity. Ionic compounds form a strong lattice of oppositely charged ions, which takes a lot of energy to break, giving them high melting points. When they are molten or dissolved, the ions are free to move, so they conduct electricity. Covalent molecules are discrete units held together by covalent bonds, with much weaker forces between molecules, so their melting points are usually lower. In water, covalent molecules don’t typically form ions, so they don’t conduct electricity. This makes the statement that pairs a property of ionic compounds with a property of covalent molecules the best fit: ionic compounds have high melting points and conduct electricity when molten or dissolved, while covalent molecules tend to have lower melting points and do not conduct electricity in water.