A compound is a substance that contains two or more elements chemically combined in fixed proportions. A molecule is a group of atoms that are chemically bonded together. All compounds are molecules, but not all molecules are compounds. For example, a molecule of water (H2O) is a compound, because it contains two elements, hydrogen and oxygen, chemically combined in a fixed proportion. However, a molecule of oxygen (O2) is not a compound, because it contains only one element, oxygen.

In addition to the difference in composition, compounds and molecules also differ in their properties. Compounds are typically more stable than molecules, and they have higher boiling points and melting points. This is because the chemical bonds between the atoms in a compound are stronger than the bonds between the atoms in a molecule.

Finally, compounds and molecules differ in their reactivity. Compounds are typically more reactive than molecules, because the chemical bonds between the atoms in a compound are more easily broken. This means that compounds are more likely to undergo chemical reactions than molecules.