The Periodic Table of the Elements contains every known element in the universe. It is used by chemists to learn about these atoms. It is made up of tiny squares, each containing a certain element. The boxes are various colors as well. Blue indicates a gas when in its natural state, a yellow square indicates a solid when in its natural state, orange identify liquids when in their natural state, and green show that the element has been discovered by man in a laboratory. Inside each square is a one or two letter abbreviation of the name of the element, the symbol. Most of these abbreviations come from the Latin or Greek names of the elements. Above the symbol for the element is the elements atomic number.
The atomic number indicates the number of protons within the nucelus of a given element. Hydrogen only has one proton, so it's number one on the Periodic Table. Helium has two protons, so it is number two, and so on. The number that appears below the symbol is the elements atomic mass number. Protons and Neutrons are each both about one atomic mass unit. Neutrons have no electrical charge, so they don't affect the electrical balance of an atom, and there can be varying numbers of them. Each one of these with a varying number of neutrons is called an isotope.