Properties of Ionic and Covalent Compounds

If you know the chemical formula of a compound, you can predict whether it contains ionic bonds, covalent bonds, or a mixture of bond types. Nonmetals bond to each other via covalent bonds while oppositely charged ions, such as metals and nonmetals, form ionic bonds. Compounds which contain polyatomic ions may have both ionic and covalent bonds.

But, how do you know if a compound is ionic or covalent just by looking at a sample? This is where the properties of ionic and covalent compounds can be useful. Because there are exceptions, you need to look at several properties to determine whether a sample is ionic or covalent, but here are some characteristics to consider:

• Most crystals are ionic compounds. This is because the ions in these compounds tend to stack into crystal lattices to balance between the attractive forces between opposite ions and the repulsive forces between like ions. Covalent or molecular compounds can exist as crystals, though. Examples include sugar crystals and diamond.
• Ionic compounds tend to have higher melting and boiling points than covalent compounds.
• Ionic compounds tend to be hard and brittle while covalent compounds tend to be softer and more flexible.
• Ionic compounds conduct electricity when dissolved in water while covalent compounds typically don't. This is because covalent compounds dissolve into molecules while ionic compounds dissolve into ions, which can conduct charge.