Atoms are very reactive species.
So in nature, atoms exist as ions or molecules .
Molecules → Atoms combine to form molecules (Hydrogen, Oxygen, Chlorine, Ozone etc.)
Atoms or molecule with charge over them are called ions (Fluoride, Chloride, Sodium, Magnesium ions)
There are some atoms that are not reactive. They exist as atoms itself . These are the Noble gases like Helium, Neon, Argon etc.