Compounds are pure substances made of atoms of two or more elements chemically combined in fixed ratios. But if these components are separated physically, each can be obtained in pure form and each meets all the criteria for compounds. Compounds are made of atoms of two or more elements. For example, O 2 and O 3 are considered forms of the element oxygen, and not compounds of oxygen.
Compounds are chemically combined elements.
Mixing 2.0 grams of H 2 with 70.9 g of Cl 2 in the dark results in a homogenous mixture of H 2 and Cl 2 . Mix the gases in the exact same proportions in the light and there is a violent explosion. The gas is now 72.9 g of HCl, a compound. Components in a homogenous mixture may influence each other's chemical behavior slightly, but there is not radical alteration in chemical and physical properties. Compounds are completely different chemically and physically from the elements that form them.