The periodic table got its name from the way the elements are arranged in rows, which are called periods. The columns of the table are called groups, some of which have specific names, such as the noble gases and the halogens.
All the elements that belong to a period contain the same number of atomic orbitals. Going down the periodic table, the number of atomic orbitals increases by one for each row. The topmost elements have one orbital for their electrons, while those at the very bottom have seven orbitals for their electrons. For the groups, elements under the same category contain the same number of electrons in their outer orbitals; these outer electrons are called valence electrons.