Chemical properties of atoms are controlled by the no. of electrons, which are determined by no. of protons in a nucleus. Number of neutrons present in the nucleus have a very little effect on chemical properties of an element. Why?
Chemical reactions are due to electromagnetic force, neutrons being neutral are not capable of participating in this type of force can not involve themselves in chemical reactions. Moreover, neutrons are present in a very small region (nucleus) inside the atom and it not easy to engage something from that region in chemical reactions (even protons are not involved in chemical reactions). Neutrons, however can be involved in nuclear reactions which do not depend solely on electromagnetic force.
It is because neutrons have no charge.