### 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.