Electronic configurations of elements and the Periodic Table

In the preceding unit we have learnt that an atom is characterised by a set of four quantum number (n) defines the main energy level known as shell.we also have studied about the filling of electrons into different subshells, also referred to as orbitals (s, p, d, f) in an atom. The distributions of electrons into orbitals of an atom is called its electronic configuration. An element's location in the Periodic Table reflects the quantum numbers of the last orbital filled. In this section we will observe a direct connection between the electronic configurations of the elements and the long form of the Periodic Table. Since the long form of the periodic table is based on the atomic numbers, there is close connection between long form of periodic table and electronic configuration of the elements. Each period of the periodic table is associated with filling of particular shell.

a) Electronic configurations in Periods

The first period contains 2 elements. The subsequent periods consists of 8, 8, 18, 18 and 32 elements respectively. The seventh period is incomplete and like the sixth period would have a theoretical maximum on the basis of quantum numbers of 32 elements. In this form of the Periodic Table, 14 elements of both sixth and seventh periods (lanthanoids and actinoids, respectively) are placed in separate panels at the bottom.

b) Groupwise electronic configurations

Numerous forms of Periodic Table have been devised from time to time, Some forms emphasise chemical reactions and valence. whereas others stress the electronic configuration of elements. A modern version, the so-called “long form” of the Periodic Table of the elements, is the most convenient and widely used. The horizontal rows (which Mendeleev called series) are called periods and the vertical columns, groups. Elements having similar outer electronic configurations in their atoms are arranged in vertical columns, referred to as groups or families