The Chart of the Nuclides shows the known nuclei in terms of their atomic number, Z, and neutron number, N. Each box represents a particular nuclide and is color-coded according to its predominant decay mode. The so-called "magic numbers," with N or Z equal to 2, 8, 20, 28, 50, 82, and 126 correspond to the closure of major nuclear shells (much like the atomic shells of the electrons) and enhance nuclear stability. Isotopes that have a magic number of both protons and neutrons are called "doubly magic" and are exceptionally stable.