Here's why:
* Isotopes are atoms of the same element (meaning they have the same number of protons) but differ in their number of neutrons.
* Protons determine the element's identity. Changing the number of protons would change the element entirely.
* Electrons are involved in chemical bonding and can be gained or lost, but this creates ions, not isotopes.
Therefore, changing the number of neutrons is the only way to create an isotope of an element.
