What Is the Difference Between an Atom and an Ion?

Atom vs. Ion

An atom can be an ion, but not all ions are atoms.
An atom can be an ion, but not all ions are atoms. Paper Boat Creative/Digital Vision/Getty Images

An atom consists of protons, usually with neutrons and electrons. An ion can be an atom or it can be a molecule, but it has a different number of protons and electrons, so it carries a net electric charge. An atom can be an ion, but not all ions are atoms. There are distinct differences between an atom and an ion.

What Is an Atom?

An atom is the defining structure of an element. Elemental atoms differ from each other by the number of protons in their nucleus.

Atoms are considered to be the basic building blocks of matter because they cannot be divided into smaller particles by any chemical process.

You can use the number of protons to tell atoms apart. For example, one way to tell oxygen atoms from nitrogen atoms would be to count the number of protons each atom has. Oxygen will have eight where nitrogen will have seven.

Stable atoms have the same number of electrons as the number of protons. These electrons form orbitals around the nucleus and cause much of the chemical properties of the element.

What Is an Ion?

When an atom's outermost orbital gains or loses electrons (also known as valence electrons), the atom forms an ion. An ion with more protons than electrons carries a net positive charge and is called a cation. An ion with more electrons than protons carries a net negative charge and is called an anion. The number of neutrons doesn't come into play, since they are electrically neutral.

Changing the number of neutrons determines the isotope.

In Summary

Atoms are the smallest unit of matter that can't be broken down chemically. Ions are atoms or molecules that have gained or lost one or more of their valence electrons and have a net positive or negative charge.