Number of Valance electrons in an outer shell

      All atoms have the same amount of electrons that can be held in each shell. A shell cannot hold more electrons than the total shown. The table above shows how many can be in a shell. To find out how many valence electrons are in an atom, just add up the total amount of electrons in the outer shell. All of these are called valence electrons. For example: Lithium has an atomic number of 3. To figure out how many shells it has refer to the chart. A shell cannot hold more electrons than the total shown. Its first shell will hold a total of 2 electrons. Its outer shell will then hold 1 electron. So lithium has two shells. The most shells an atom can have is seven. Notice that there are seven rows on the periodic table of elements. Therefore the first row has elements that have only one shell, the second row has elements that have two shells, and so on and so forth.