How Are Atoms and Molecules Related?

By Jon Stefansson
aspartame molecule image by Vladislav Gajic from

Atoms are the basic building blocks of everything around us, from furniture to animals and plants and the air we breathe. Quantum mechanics is a field which has received increased attention recently with the opening of the Large-Hadron Collider by the European Organization for Nuclear Research (CERN).


Atoms are a basic unit of matter. Different types of atoms make up everything in the universe and are themselves made up of different parts. The three basic particles within an atom are protons, electrons and neutrons. Protons carry a positive electric charge, electrons carry a negative charge and neutrons carry no charge. Protons and neutrons join together to form the nucleus of an atom, while electrons circle or orbit the nucleus. At one time, protons, electrons and neutrons were thought to be the smallest things in the universe until the discovery of quarks in 1968. Quarks make up the insides of protons and neutrons and are inconceivably tiny.


Molecules are groups of atoms joined together by one of two types of bonds. Molecules made up of different types of atoms constitute the larger building blocks of the universe. Molecular structures are described by how many of each type of atom they contain. For example, a water molecule consists of two atoms of hydrogen bonded to one oxygen atom. Hydrogen is abbreviated to the letter H and oxygen to the letter O, and so H2O is the molecular description of water.

Ionic Bonds

Atoms tightly connected by attractive forces to form molecules are said to be bonded. The two different types of bond are "ionic" and "covalent." An ionic bond can form when two atoms meet and an electron is permanently transferred from one to the other. For example, when a sodium atom meets a chlorine atom, the solitary electron from the sodium is permanently transferred to the chlorine atom, binding the two together extremely tightly. This fusion of sodium and chlorine creates a sodium chloride, or salt, molecule.

Covalent Bonds

A covalent bond is formed when the electrons of two atoms overlap. As a result, the nuclei of both atoms (made up of the protons and neutrons) are held together to form a molecule. Atoms of different types can make differing numbers of covalent bonds at the same time, to bind more than two atoms together.

Fun Facts

If a hydrogen atom were the size of a thumbnail, the orbit of its electrons would be a mile wide. If a quark inside a proton were the size of a thumbnail, the proton would be roughly 1,000 miles across.