Here's why:
* Protons are positively charged particles found in the nucleus of an atom.
* Neutrons are neutral particles also found in the nucleus.
* Electrons are negatively charged particles that orbit the nucleus.
The number of protons is what defines an element. For example, all carbon atoms have 6 protons, all oxygen atoms have 8 protons, and so on.
* Changing the number of neutrons results in an isotope of the same element (e.g., carbon-12 and carbon-14).
* Changing the number of electrons results in an ion, either positively or negatively charged.
Therefore, the atomic number is a fundamental property of an element and determines its identity.
