The idea that the world around us is made up of tiny particles (pieces) has existed for centuries. Today we know that all matter (materials) are made of atoms.
Atoms are the basic building blocks of all matter. All substances are made out of atoms. Atoms are so tiny that there would be roughly 10 000 000 000 000 atoms in the dot at the end of this sentence.
Atoms are not usually found on their own. Two or more atoms bonded together are called a molecule. For example an oxygen molecule consists of two oxygen atoms joined together.
Some common molecules: