Question

How did the position of isotopes of chlorine get fixed in modern periodic table

Answer 1

Originally Answered: Why don’t we consider isotopes in the periodic table?

Modern periodic table was made considering atomic no. of elements. The elements were arranged according to increasing atomic no. And atomic no. depends upon the total no. of electrons present in neutral atom or precisely total no. of protons in nucleus.

The elements are arranged systematically according to outer electronic configuration into groups and families in periodic table. Since the outer Valence electrons participate in reactions, hence chemical and physical properties are dependent on electronic configuration.

Now, isotopes of an element differ in mass no. (Sum of protons and neutrons in nucleus) but have same atomic no. i.e. they have same no. of protons but different no. of neutrons.

Thus, isotopes of an element are placed in same position. Or we can say that isotopes are not considered in periodic table.