Here's why:
* Protons: Determine the element's identity. The number of protons is called the atomic number.
* Neutrons: Contribute to the atom's mass. The number of neutrons can vary within an element, creating isotopes.
For example:
* Carbon has an atomic number of 6, meaning it always has 6 protons.
* Carbon-12 has 6 neutrons, so it has an equal number of protons and neutrons.
* Carbon-14 has 8 neutrons, making it an isotope of carbon with a different mass.
Key takeaway: A neutral atom has the same number of protons and electrons, but the number of neutrons can vary.