The periodic table is composed of seven horizontal rows or periods and is numbered between 1 and 7. Elements are arranged in the periodic table in the increasing order of their relative atomic masses. In Mendeleev’s periodic table, the groups were divided into two subgroups.
- Groups from I to VII are meant for normal elements and group VIII is for transition elements.
- Groups from I to VII have been divided into two subgroups, while group VIII is meant for three elements.