The elements on the periodic table are organized in several basic ways. The first is very straightforward. Going from left to right (from the top rows to the bottom ones) on your periodic table, you will find that the atomic number always changes by one. The atomic number represents how many protons and electrons are present (the number of protons and electrons in an element are always the same). For an elaborated explanation of atomic numbers and protons, electrons, and neutrons, please refer to our What is the basic structure of an atom?", and How do structures of atoms differ?" pages.

        Another way that the elements on the periodic table are organized is by their orbitals. When you go from top to bottom on the periodic table, you will find that the number of orbitals increase. Below is a diagram of this.

        The check marks represent "empty slots" which are basically parts of orbitals that are empty. Note that there are three circles, or orbitals, around the nucleus (the smallest circle) in this particular element of phosphorus. The second smallest circle around the nucleus would be the first orbital (sorry you can't see the labeling!), and the smallest after that would be the second orbital, and the third and largest circle around that is the third orbital (the one with empty slots).

  What is the basic structure of an atom?

  How do the structures of atoms differ?