 In this chapter we are going to explore the difference between physical properties and chemical properties of substances. If we observe the magnesium metal ribbon that we have, we'll look at some of the physical properties first. We first see that it is a solid at room temperature, that is a shiny metal, that it conducts electricity. Those are some of its important physical properties. At room temperature, the magnesium does not react very rapidly with the oxygen in the air. If we bring in a little bit of heat, the magnesium rapidly reacts with the oxygen in the air. The reaction is very exothermic, as you can see from the light emitted. The white smoke is actually very finely divided magnesium oxide. What we are left with is the ionic compound, magnesium oxide, which is a white solid. Unlike the flexible metal, the ionic compound is a very brittle white solid. So we have lost the properties of the original metal and we have created new properties for the ionic compound.