||The very small, very dense, positively charged center of an atom
containing protons and neutrons, as well as other subatomic particles.|
- The small, central, positively charged region of an atom. Except for the
nucleus of ordinary hydrogen, which has only a proton, all atomic nuclei
contain both protons and neutrons. The number of protons determines the total
positive charge or atomic number. This number is the same for all the atomic
nuclei of a given chemical element. The total number of neutrons and protons
is called the mass number.