How does the atomic number of an element identify it?
The atomic number,
Because most matter is neutral, if there are 26 protons within the nucleus, there MUST be 26 electrons, fundamental negatively charged particles of negligible mass associated with the NEUTRAL element. Note that the nucleus can contain different numbers of neutrons, fundamental massive nuclear particles with neutral charge, which act to bind the nucleus together. The presence of neutrons gives rise to the existence of isotopes: atoms of the same element with different atomic masses.