The Nucleus

At the center of an atom is the nucleus. The nucleus contains the nucleons which are the protons and neutrons. Because most of the weight of an atom comes from the nucleus, electrons can be said to weigh little.

The formula for finding out the number of protons and neutrons is:

Mass number (A) = Number of protons + number of neutrons


Some common comparisons:
Number of protons = Atomic number
Mass number = Nucleon Number