How do atoms become molecules?

As atoms come together to form molecules, chemical bonds bind them together. These bonds form as a consequence of sharing or exchanging electrons between the atoms. It is only the electrons that are ever active in bonding in the outermost shell. The atoms in a molecule may be from the same element or from different elements. For example, the molecule Ozone (O3) is formed when three atoms of Oxygen bond together. On the other hand, H2O is formed when two different atoms, Hydrogen and Oxygen, bond together.