difference between atom molecule element and compound

Atom is the smallest indivisible part of matter which retains its identity ( this last part is added because, though atoms can be divided into Protons, neutrons and electrons; thoae particles have no identity e.i, there's no difference between a oxygen electron and a hydrogen electron). Actually an atom gives any element it's identity.

A molecule now, is a formed when two or more atoms combine. If the same kind of atoms combine, the substance they form will be called an element ( remember, same type of atoms). Now comes the catch. If two different types of atoms combine to form a molecule, the pure substance formed by these molecules will be called a compound. This bit is very important.

I repeat, a compound is a pure substance formed by the molecules composed of different types of atoms ( say hydrogen and oxygen atoms combine to form a water molecule and many millions of water molecules will form the compound

• Atom : simplest particle. Very small, cannot be further separated. Noble gases are monoatomic, composed of a single atom.
• Molecule : made of 2 or more atoms. Examples include diatomic halogen group 7, oxygen gas, nitrogen gas, hydrogen gas.