Read this page, which covers electron configurations and the arrangement of the periodic table. An electronic configuration is a listing of the occupancy of an atom's electrons amongst its orbitals. The periodic table was purposefully designed to reflect the chemical nature of each element. Metals, for example, are on the left-hand side, while noble gases are on the right. Halogens are always to the immediate left of the noble gases. By the end of this section, you should be able to identify these and other groups on a periodic table. Remember that a group is a vertical column, while a period is a horizontal row.