Element or Compound?
An element is a substance that contains only one type of atom. An element may be monatomic like helium (He), a simple molecule like Oxygen (O2), or even large structures like pure Copper (Cu).
A compound is a molecule containing two or more different types of atoms. For example, Water or (H2O) is a compound containing one oxygen atom and two Hydrogen atoms. Based on this definition, compounds can be molecules but can not be monatomic.