Chemical changes are changes on the atomic level due to bonds forming or breaking, creating new compounds; burning a candle is an example. Candle wax functions as a fuel that reacts with oxygen in the air when exposed to high enough temperatures, producing carbon dioxide, water vapor, light and heat.
Chemical changes occur during chemical reactions between elements or compounds, and they are responsible for all of the complex compounds in the universe. The likelihood of an element or compound undergoing a chemical change depends on its atomic structure and is called its reactivity. A higher reactivity correlates to an increased tendency to form bonds.