Answer the following question given this paragraph: 

Many compounds form molecules, but ionic compounds form crystals instead. A crystal consists of many alternating positive and negative ions bonded together in a matrix. Look at the crystal of sodium chloride (NaCl) in the Figure below . The sodium and chloride ions are attracted to each other because they are oppositely charged, so they form ionic bonds.


Q: What type of compounds can form crystals?


A:
ionic compounds