Here's why:

* Atoms are the basic building blocks of matter. They consist of a nucleus containing protons (positive charge) and neutrons (no charge), and electrons (negative charge) orbiting the nucleus.

* Ions are atoms that have gained or lost electrons.

* Cations are positively charged ions formed when an atom loses electrons.

* Anions are negatively charged ions formed when an atom gains electrons.

In summary, ions are formed by a change in the number of electrons surrounding an atom's nucleus. The number of protons (which determines the element) remains the same.