Atoms are reeeeally small. They are so small that you can’t see them with just your eye. It takes as many as 10 million of them side-by-side to measure a single millimeter. In fact, atoms are the smallest pieces of “stuff” that are still considered “stuff.” If you take something and break it into tiny pieces, and then break it into tinier pieces, and keep going, the smallest part you’d be left with (and still have the same substance that you started with) is an atom. Atoms are the building blocks of all matter. Everything is made of only 109 different kinds of atoms, called elements. 92 of these elements occur naturally, but the rest of them – ones like Technetium and Promethium have only been found in distant stars and Californium and Einsteinium – are only made in laboratories. A molecule is born any time two or more atoms combine together.