Question

why isotopes of an element are chemically similar

Answer 1

Isotopes of an element have the same number of electrons. They have the same electronic distribution in various orbitals around the nucleus.  They differ in the number of neutrons in the nucleus. They have the same atomic number Z and have different mass number M.

The chemical properties of an element are dependent on the electronic configuration inside the atoms. Since Isotopes have same number electrons in the same orbitals, their chemical properties remain same.

Their physical properties like color, mass, weight, density shape or state may be different from each other.

Answer 2

because isotopes are atoms of same element which have similar atomic number but different mass number. As atomic number is same so same no. of electrons and hence electronic configuration is same. Due to similar number of valence electrons there exists a similarity in their chemical properties. For eg. the two isotopes of carbon, C-12 and C-14, both have same atomic number i.e 6. Thus, their electronic configuration is 2,4. So, valency for both is 4 and hence there exists similarity in chemical properties.