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24.2: Nuclear Notation

Difficulty Level: At Grade Created by: CK-12
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Lesson Objectives

The student will:

  • read and write complete nuclear symbols.


  • nuclear symbol
  • nucleon


Recall that the identity of an atom is determined by the number of protons in the nucleus of the atom. In the chapter “The Atomic Theory,” the number of protons in the nucleus of the atom is also defined as the atomic number. In comparison, the mass number accounts for the total number of protons and neutrons, also called nucleons, in the nucleus of an atom. Nucleon is the collective name for protons and neutrons. One way to convey the mass number and the atomic number of an element is by using nuclear symbol. In this lesson, we will learn about how to read and write nuclear symbols, which you will find useful later on in this chapter.

The Complete Nuclear Symbol

The complete nuclear symbol contains the symbol for the element and numbers that relate to the number of protons and neutrons in that particular nucleus. To write a complete nuclear symbol, the mass number is placed at the upper left (superscript) of the chemical symbol and the atomic number is placed at the lower left (subscript) of the symbol. The complete nuclear symbol for helium-4 is drawn below.

The following nuclear symbols are for a nickel nucleus with 31 neutrons and a uranium nucleus with 146 neutrons.

\begin{align*}^{\textbf{59}}_{\textbf{28}}\textbf{Ni} \qquad \quad ^{\textbf{238}}_{\textbf{92}}\textbf{U}\end{align*}

In the nickel nucleus represented above, the atomic number 28 indicates the nucleus contains 28 protons, so it must contain 31 neutrons in order to have a mass number of 59. The uranium nucleus has 92 protons, as do all uranium nuclei, and this particular uranium nucleus has 146 neutrons. Another way of representing these nuclei would be Ni-59 and U-238.

Recall that atoms of an element are identical in every way but the mass numbers. This mass difference results from nuclei of the same element having a different number of neutrons. Remember that atoms with the same atomic number but a different mass number are called isotopes. Hydrogen, for example, has three isotopes, shown in the figure below. All three of hydrogen's isotopes must have one proton (to be hydrogen), but they have zero, one, or two neutrons in the nucleus.

Originally, the names protium, deuterium, and tritium were suggested for the three isotopes of hydrogen. Nuclear scientists today use the names hydrogen-1, hydrogen-2, and hydrogen-3, but occasionally you will see or hear the other names.

Lesson Summary

  • The complete nuclear symbol has the atomic number (number of protons) of the nucleus as a subscript at the lower left of the chemical symbol and the mass number (number of protons + neutrons) as a superscript at the upper left of the chemical symbol.

Review Questions

  1. Write the complete nuclear symbol for a nucleus of chlorine that contains \begin{align*}17\end{align*} protons and \begin{align*}20\end{align*} neutrons.
  2. Write the complete nuclear symbol for a nucleus of oxygen that contains \begin{align*}8\end{align*} protons and \begin{align*}10\end{align*} neutrons.
  3. If a nucleus of uranium has a mass number of \begin{align*}238\end{align*}, how many neutrons does it contain?
  4. In the nuclear symbol for a beta particle, what is the atomic number?
  5. Is it possible for isotopes to be atoms of different elements? Explain why or why not.
  6. How many neutrons are present in a nucleus whose atomic number is one and whose mass number is one?
  7. Name the element of an isotope whose mass number is \begin{align*}206\end{align*} and whose atomic number is \begin{align*}82\end{align*}.
  8. How many protons and how many neutrons are present in a nucleus of lithium\begin{align*}-7\end{align*}?
  9. What is the physical difference between a \begin{align*}\mathrm{U}-235\end{align*} atom and a \begin{align*}\mathrm{U}-238\end{align*} atom?
  10. What is the difference in the chemistry of a \begin{align*}\mathrm{U}-235\end{align*} atom and a \begin{align*}\mathrm{U}-238\end{align*} atom?

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