Why Is The Periodic Table Arranged The Way It Is?

The periodic table is arranged by atomic number, which is the number of protons in an element’s nucleus. The elements are arranged in order of increasing atomic number. The periodic table is also arranged by groups and periods. The elements in a group have the same number of electrons in their outermost orbital. The elements in a period have the same number of electron shells. At the bottom of the periodic table are two additional rows of elements containing a total of fourteen elements. The top row elements are called Lanthanides or rare earth elements. The bottom row of elements are called Actinides. These begin at element number 90 and end at 103. However, there are elements beyond 103, as well as a continuous effort to push for higher order elements.