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.)
Ions →
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.