Question Video: Determining the Number of Nucleons in an Atom of Sodium Given the Mass Number Chemistry • 7th Grade

An atom of sodium has a mass number of 23. What is the total number of protons and neutrons in the nucleus of the atom?

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Video Transcript

An atom of sodium has a mass number of 23. What is the total number of protons and neutrons in the nucleus of the atom?

To answer this question, we need to determine the number of nucleons, the total number of protons and neutrons, in an atom of sodium. Atoms are composed of positively charged protons, neutral neutrons, and negatively charged electrons. One way to concisely represent the number of some of these particles in an atom is to use nuclide notation, or AZE notation. In nuclide notation, the capital E represents the chemical symbol of the element. If, for example, we wanted to construct the nuclide notation of an atom of sodium, we would write Na, the chemical symbol of sodium, in place of E.

Z represents the atomic number. The atomic number is unique for each element and indicates the number of protons in all atoms, ions, and isotopes of that element. The atomic number is frequently written above the chemical symbol in each cell of the periodic table. The element sodium has an atomic number of 11, meaning that an atom of sodium has 11 protons. A represents the mass number. The mass number is equal to the sum of the number of protons and neutrons in the nucleus.

We are told in the question that the atom of sodium has a mass number of 23. We can substitute 23, the mass number of the sodium atom, and 11, the number of protons in a sodium atom, into the equation. We can then solve to determine that the atom of sodium has 12 neutrons. The question asked for the total number of protons and neutrons in the nucleus of the atom. The total number of nucleons is 11 plus 12, or 23, the same as the mass number. Therefore, the total number of protons and neutrons in an atom of sodium that has a mass number of 23 is 23.