What Is an Atom?

An atom is the basic unit of an element. An atom is a form of matter which may not be further broken down using any chemical means. A typical atom consists of protons, neutrons, and electrons.

Atom Examples

Any element listed on the periodic table consists of specific atoms. Hydrogen, helium, oxygen, and uranium are examples of types of atoms.

What Are Not Atoms?

Some matter is either smaller or larger than an atom. Examples of chemical species that are not typically considered atoms includes particles that are components of atoms: protons, neutrons, and electrons. Molecules and compounds consist of atoms but are not themselves atoms. Examples of molecules and compounds include salt (NaCl), water (H₂O) and methanol (CH₂OH). Electrically charged atoms are called ions. They are still types of atoms. Monoatomic ions include H⁺ and O^2-. There are also molecular ions, which are not atoms (e.g., ozone, O₃^-).

The Gray Area Between Atoms and Protons

Would you consider a single unit of hydrogen to be an example of an atom? Keep in mind, most hydrogen "atoms" do not have a proton, neutron, and electron. Given that the number of protons determines the identity of an element, many scientists consider a single proton to be an atom of the element hydrogen.