What is atomic weight?
atomic weight The nuclei of atoms also contain neutrons, which help hold the nucleus together. A neutron has no electrical charge and is slightly more massive than a proton. Because a neutron can decay into a proton plus an electron (the essence of beta decay), it is sometimes helpful to think of a neutron as an electron and a proton blended together, although this is at best an oversimplification. Because a neutron has no charge, a neutron has no effect on the number of electrons orbiting the nucleus.
However, because it is even more massive than a proton, a neutron can add significantly to the weight of an atom. The total weight of an atom is called the atomic weight. It is approximately equal to the number of protons and neutrons, with a little extra added by the electrons. The stability of the nucleus, and hence the atom’s radioactivity, is heavily dependent upon the number of neutrons it contains.