### Video Transcript

Nuclide notation is used to summarize some of the properties of an atom or an ion. Which of the following properties is not directly expressed in nuclide notation? (A) Atomic number, (B) charge, (C) element symbol, (D) neutron number, or (E) mass number.

Nuclide notation, or AZE notation, is a way to represent some of the properties of an atom or ion. The nuclide notation of an atom has three main components, A, Z, and E. Let’s summarize each of these components while writing the nuclide notation for this atom of lithium. E represents the chemical symbol or element symbol of the element as it appears on the periodic table. The element symbol of lithium is Li. So this is written in place of E. In answering the question, we need to determine which of the properties given is not directly expressed in nuclide notation. The element symbol is expressed in nuclide notation. Therefore, answer choice (C) cannot be the answer to this question.

The letter A in nuclide notation represents the mass number. The mass number is the number of nucleons in an atom or ion, where nucleons collectively refers to protons and neutrons. The atom of lithium shown has three protons and three neutrons for a total of six nucleons. So we can replace the letter A in the nuclide notation with six, the mass number of the lithium atom shown. Mass number is directly expressed in nuclide notation. So answer choice (E) cannot be the answer to this question.

The letter Z in nuclide notation represents the atomic number. The atomic number is the number of protons in an atom or ion. The atomic number is frequently written above the element symbol in each cell on the periodic table. An atom of lithium, like the one drawn, has three protons. So we can replace the letter Z in nuclide notation with three, the atomic number of lithium. The atomic number is expressed in nuclide notation, so answer choice (A) cannot be the answer to this question.

We have now examined the nuclide notation of an atom, but what about the nuclide notation of an ion? An ion is a species with a net electrical charge. We can include the charge in nuclide notation by writing the charge as a superscript value following the element symbol. The lithium ion shown has a charge of one plus. As the one of a one plus charge is often omitted, we can simply write a plus sign to the right of the element symbol. As charge can be expressed directly in nuclide notation, answer choice (B) cannot be the correct answer to this question.

That leaves us with answer choice (D) neutron number. While the number of neutrons is not directly expressed in nuclide notation, it can be calculated if both the mass number and atomic number are known. We can now answer the question. The property that is not directly expressed in nuclide notation is answer choice (D) neutron number.