Atoms
If a water molecule could be magnified sufficiently it would be seen to consist of three smaller particles closely bound together. These three particles are ATOMS, two of hydrogen and one of oxygen.
The water is a compound, the oxygen and hydrogen are elements. Every element has atoms of its own type. There are 92 naturally occurring elements and therefore 92 types of naturally occurring atoms.
Every molecule consists of atoms. Molecules of elements contain atoms of the same types, for example the hydrogen molecule consists of two atoms of hydrogen joined together, the oxygen molecule consists of two atoms of oxygen joined together, but the molecules of compound contain different atoms joined together.
Most molecules contain more than one atom but some elements can exist as single atoms. In such a case the atom is also the molecule. For example the Helium atom is also the Helium molecule.
An atom is the smallest indivisible particle of an element which can take part in a chemical change. The term ‘atomic structure' is use when talking about elements.