The building up principle gives the ground state electronic configurations of the elements, and there are similarities running through those configurations.

The elements can be arranged into groups which all have the same generic electronic configuration, specifically the structure of the valence shell outside a noble gas core. These groups form the periodic table:

The Periodic Table
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18
I II III IV V VI VII VIII
H He
Li Be B C N O F Ne
Na Mg Al Si P S Cl Ar
K Ca Sc Ti V Cr Mn Fe Co Ni Cu Zn Ga Ge As Se Br Kr
Rb Sr Y Zr Nb Mo Tc Ru Rh Pd Ag Cd In Sn Sb Te I Xe
Cs Ba La-Lu Hf Ta W Re Os Ir Pt Au Hg Tl Pb Bi Po As Rn
Fr Ra Ac-Lr

The elements in the block La-Lu are known as the Lanthanide series, and have electronic configurations which show the 4f subshell is occupied across the series:

La Ce Pr Nd Pm Sm Eu Gd Tb Dy Ho Er Tm Yb Lu

The elements in the block Ac-Lr are known as the Actinide series, and have electronic configurations which show the 5f subshell is occupied across the series:

Ac Th Pa U Np Pu Am Cm Bk Cf Es Fm Md No Lr

Each row in the periodic table is known as a period, and corresponds to the completion of the s and p subshells of a given principal quantum number shell. The principal quantum number, n, is also the period number.

Each column in the periodic group is known as a group, and elements in a group all exhibit similar chemistry. The group numbers, G, from 1 to 18, are related to the number of valance electrons in elements within those groups. In the s and d blocks, the number of valence electrons is equal to G, and in the p block it is G-10.