The electronic configuration of an atom shows someone the amount of electrons that an element has in each shell, without them having to draw an electron diagram. For example, fluorines electronic configuration is 2.7, so in its first shell there will be two electrons and in its second shell, there will be seven electrons. By looking at the group an element is in the periodic table, a person can work out the amount of electrons that an atom has in its outer shell.
Electronic Configurations of the first 20 elements
In the periodic table, as you go across the periods, the amount of electrons in the outer shell of the atoms increases by one. As you go down the groups in the periodic table, all of the elements down the column have the same amount of electrons in their outer shells.