The two isotopes of chlorine, chlorine-35 and chlorine-37, have the same chemical properties because they have the same number of protons and electrons.

Here's why:

* Protons determine the element: The number of protons in an atom's nucleus defines what element it is. Both chlorine isotopes have 17 protons, making them chlorine.

* Electrons determine chemical behavior: The number of electrons in an atom's outermost shell dictates how it interacts with other atoms, forming chemical bonds. Both isotopes have 17 electrons, giving them identical electronic configurations.

Isotopes differ only in the number of neutrons they have. Neutrons contribute to the atom's mass, but they don't participate in chemical bonding. Therefore, the difference in neutron count between the two chlorine isotopes has no impact on their chemical properties.

In summary:

* Same protons: Same element (chlorine)

* Same electrons: Same chemical behavior

This is why chlorine-35 and chlorine-37 behave identically in chemical reactions. Their difference in mass is only noticeable in certain physical properties like atomic weight.