The properties of ionic compounds result from the multitude of interionic attractions in the crystalline solid. Every ion is attracted by a host of oppositely charged ions even though the ions may be quite far away. The electrostatic force radiates out from electrically charged particles and gradually decreases with distance. This creates a solid where the total of all these forces acting on an ion can be very great. Ionic compounds are combinations of a metal and nonmetal or a metal and a polyatomic anion.

EXAMPLES: NaCl, CaF₂, Al(NO₃)₃, FeCl₂

Molecular compounds are poor conductors of heat and electricity because the electrons are locked up in covalent bonds. There are no mobile electrons or charged particles.

EXAMPLES: CO, CH₄, CO₂, H₂O, PCl₅

The melting point (temperature at which the solid begins to liquefy) of a material is directly connected to the energy needed to break up the solid. Solid water a.k.a. ice melts below room temperature at 0^o or 32^oF. Butter melts around room temperature and plastics usually melt above room temperature.

The boiling point (temperature at which a liquid begins to boil) of a material is directly connected to the energy needed to break up the liquid. Covalent nitrous oxide, N₂O, and carbon dioxide, CO₂, boil below room temperature. Even water has a boiling point which at 100^oC, which is much less than what is observed for low melting ionic materials ( about 500 to 600 degrees C).

The structure of solids of ionic and covalent materials is different. A covalent molecule is a separate unit from its surrounding molecules. The molecules are attracted to one another by temporary imbalances in the electron clouds around the total molecule. The electrons in molecules are constantly randomly moving. This random movement accidently creates imbalances where a spot in a molecule will have a slight positive or negative charge. These temporary charge imbalances produce weak attractions between neighboring molecules. The boiling point is proportionately low. Factors like molecule mass and shape influence the melting and boiling points. Large molecules have higher melting points because the larger molecule tends to have more surfaces over which electrons can interact with neighboring molecules. Polymers have higher melting points than the smaller monomers that are the building blocks for polymers.