Anand Classes Notes explain the arrangement of elements in the periodic table follows a specific order based on the filling of electrons in atomic orbitals. From the fourth period onward, the pattern becomes more complex due to the involvement of d- and f-block orbitals. These periods include not only s- and p-block elements but also transition and inner transition elements. Understanding how these orbitals are filled explains why some periods have 18 or even 32 elements, unlike the shorter first three periods.