In isotopic notation, what do A and Z represent?

In isotopic notation, what do A and Z represent?

• A. A is atomic number, Z is mass number
• B. A is number of protons, Z is neutrons
• C. A is mass number, Z is atomic number
• D. A is electrons, Z is protons

Answer: (C)

In isotopic notation, you’re reading two pieces of information about the nucleus: how heavy it is and how many protons it contains. The mass number, A, is the total number of nucleons (protons plus neutrons). The atomic number, Z, is the number of protons, which also fixes the element and, in a neutral atom, equals the number of electrons. So A is mass number and Z is atomic number. You can find the number of neutrons by calculating A − Z. For example, nitrogen-14 has A = 14 and Z = 7, so there are 7 neutrons.

In isotopic notation, you’re reading two pieces of information about the nucleus: how heavy it is and how many protons it contains. The mass number, A, is the total number of nucleons (protons plus neutrons). The atomic number, Z, is the number of protons, which also fixes the element and, in a neutral atom, equals the number of electrons. So A is mass number and Z is atomic number. You can find the number of neutrons by calculating A − Z. For example, nitrogen-14 has A = 14 and Z = 7, so there are 7 neutrons.