The Atom 
Atoms are the building blocks of matter. They are the basis of all the structures and organisms in the universe. The planets, the sun, grass and trees, the air we breathe, and people are all made up of atoms.
There are approximately 100 different types of atom, although many of these exist in very small quantities. Every chemical element is one type of atom, such as hydrogen (H), aluminium (Al) and iron (Fe).