Isotone Isotone Two nuclides are isotones if they have the same neutron number "N", but different proton number "Z". For example, boron-12 and carbon-13 nuclei both contain 7 neutrons, and so are isotones. Similarly, S, Cl, Ar, K, and Ca nuclei are all isotones of 20 because they all contain 20 neutrons. Despite its similarity to the Greek for "same stretching", the term was formed by the German physicist K. Guggenheimer by changing the "p" in "isotope" from "p" for "proton" to "n" for "neutron". The largest numbers of observationally stable nuclides exist for isotones 50 (five: Kr, Sr, Y, Zr,
Atomic nucleus electromagnetic potential well which binds electrons in atoms. Some resemblance to atomic orbital models may be seen in a small atomic nucleus like that of helium-4, in which the two protons and two neutrons separately occupy 1s orbitals analogous to the 1s orbital for the two electrons in the helium atom, and achieve unusual stability for the same reason. Nuclei with 5 nucleons are all extremely unstable and short-lived, yet, helium-3, with 3 nucleons, is very stable even with lack of a closed 1s orbital shell. Another nucleus with 3 nucleons, the triton hydrogen-3 is unstable and will decay into