Atoms are the smallest portion of an element that still retains the properties of that element.
All neutral atoms have the same number of protons as electrons making the net charge of a neutral atom 0. Atomic Number is equal to the number of protons in the nucleus. It defines the element. The Mass Number or Atomic Weight is the weighted average of the number of protons and neutrons in the atoms of an element. Isotopes Isotopes are atoms of the same element with a different number of neutrons.