Taking the example of an element of atomic number 16, explain how the electronic configuration of the atom of an element relates to its position in the Modern Periodic Table and how valency of an element is calculated on the basis of its atomic number.

Explanation

In the Modern Periodic Table, the number of electron shells present in the atom of an element gives its period number while the number of valence electrons decides its group number. For example, element of atomic number 16 has the electronic configuration 2, 8, 6. Since it has 3 electron shells, it is placed in the 3rd period and since it has 6 valence electrons, it is placed in 10+6 = 16th group. Since the element needs 2 more electrons to attain a noble gas configuration, its valency is 2.