Difference between an Atom, a Molecule and a Compound

Let’s take a look at the difference between an atom, molecule, and a compound.

The smallest unit of matter is an atom.

Each atom is made of smaller particles known as subatomic particles.

In the nucleus, or middle of an atom are two subatomic particles the proton and neutron. The positively charged articles in the nucleus of an atom are called protons

The number of protons in the nucleus is the defining property of an element, and is referred to as the atomic number.  

The uncharged particles in the nucleus are called neutrons.

Orbiting the nucleus of an atom is a cloud of negatively charged particles called electrons.

The electrons are much smaller in mass than protons and neutrons.

The mass of an atom is based on the sum of the mass of the protons and neutrons.


A molecule is when you take individual atoms and physically connect them together. The atoms are stuck together by either sharing the electrons which is a covalent bond or by transferring electrons which is an ionic bond.A molecule like ozone can be two or more of the same atom.

For example, when you stick two hydrogen atoms to one oxygen atom you get water.

In addition you have compounds. A compound occurs when you combine elements together chemically, but for it to be a compound, those elements must be different.

An element is a pure substance consisting only of atoms that all have the same numbers of protons. Chemical elements cannot be broken down into simpler substances by chemical means. You can find all of the elements on the Periodic Table of the Chemical Elements

An example of a compound would be sugar. When you combine carbon, hydrogen, and oxygen you get sugar.