Nuclear Symbol Notation

Nuclear Symbol Notation
Nuclear symbol notation includes the element symbol, the mass number, and the atomic number.

Nuclear symbol notation is a way of identifying the isotopes of elements. Here are two ways of writing nuclear symbols, along with examples.

What Is Nuclear Symbol Notation?

Basically, the nuclear symbol is a type of shorthand notation that identifies the element (by symbol or atomic number) and the mass number of the element. The mass number is the sum of the number of nucleons (protons and neutrons) in the atomic nucleus. Isotopes of an element have distinct mass numbers because they contain different numbers of neutrons.

There are two ways of writing the symbols. The first is just the element name or symbol, followed by a dash and the mass number. For example, carbon-14 or C-14 both indicate the isotope of carbon that has 14 nucleons. The other method, sometimes called the AZE or AZX notation, lists the mass number as a superscript and the atomic number as a subscript before the element symbol. Ideally, the mass number is right on top of the atomic number, but the two numbers don’t line up in ordinary text. The general form for the notation is:



  • A is the mass number or number of nucleons (protons + neutrons)
  • Z is the atomic number or number of protons
  • X is the element symbol

For example, 146C and 126C are the nuclear symbols for the isotopes carbon-14 and carbon-12, respectively.

The number of electrons is not included in the nuclear symbol because electrons are not in the nucleus. That being said, ions of isotopes may be written as nuclear symbols, followed by electric charge as a superscript. For example, 11H+ indicates a protium (hydrogen-1) ion with a +1 electrical charge.

Example Problems Using Complete Nuclear Symbol Notation

How to Write a Nuclear Symbol

For example, with the nuclear symbol for an atom having 32 protons and 38 neutrons.

  1. First, use a periodic table and look up which element has 32 protons. This is the atomic number. The element is germanium, which has the symbol Ge. The “X” in the nuclear symbol is Ge.
  2. The atomic number Z is the number of protons. So, Z is 32.
  3. Next, find the mass number. Add up the number of protons (32) and neutrons (38). The mass number is 70.
  4. Put it all together: 7032Ge or germanium-70

Finding the Number of Neutrons

Other typical problems ask you to find the number of neutrons in an atom given its nuclear symbol. For example, find the number of neutrons in an atom of 188O.

This question tests your understanding of the parts of the nuclear symbol. The number 18 is A or the sum of the protons and neutrons. The number 8 is the atomic number or number of protons.

A = Z + N
N = A – Z
N = 18 – 8 = 10

You can use the other nuclear symbol notation just as easily, although you’ll need a periodic table. For example, find the number of neutrons in an atom of uranium-238.

The “238” is the mass number A (protons + neutron) and you know the element is uranium (U), but you need to look up its atomic number Z. From the periodic table, the atomic number of uranium is 92.

A = Z + N
N = A – Z
N = 238 – 92 = 146

Note that uranium-238 is the most common isotope of uranium, even though it contains a different number of protons and neutrons. For the lighter elements, the most stable and abundant isotope has equal numbers of protons and neutrons.


  • Choppin, G.; Liljenzin, J. O. Rydberg, J. (1995). Radiochemistry and Nuclear Chemistry (2nd ed.). Butterworth-Heinemann.
  • Connelly, N. G.; Damhus, T.; Hartshorn, R. M.; and Hutton, A. T. (2005). Nomenclature of Inorganic Chemistry – IUPAC Recommendations. The Royal Society of Chemistry.
  • Scerri, Eric R. (2007). The Periodic Table. Oxford University Press. ISBN 0-19-530573-6.