For example the closest or first energy level can only hold two electrons. The second energy level can hold 8 electrons and they have more energy than those in the first shell. Click here to get a rough idea of what it might be like to fly through the electrons surrounding an atom and see the nucleus. Each kind of atom is called an element . The answer is that atoms combine.
Atoms join with other atoms in order to try to fill up their outermost shell with electrons.
Charged atoms are called ions and this kind of combining is called an ionic bond . A chemical formula gives the symbol for each kind of atom and tells you how many of them joined to form that particular kind of molecule. An example is H2O which shows water is made of two atoms of hydrogen stuck to one atom of oxygen. In order to truly understand life you must understand what a chemical reaction is. Under certain circumstances a molecule can be broken apart and its atoms rearranged to make some completely different substance.