The notation for an isotope is typically written in two main ways: 1. Standard Nuclear Notation: $\boxed{^{A}_{Z}\text{X}}$ $\text{X}$ is the chemical symbol* of the element (e.g., Cl for Chlorine). $\text{A}$ is the mass number*, which is the total number of protons and neutrons in the nucleus. It's written as a superscript on the top left. $\text{Z}$ is the atomic number*, which is the number of protons in the nucleus. It's written as a subscript on the bottom left. Example: For Chlorine-37, the notation is $\boxed{^{37}_{17}\text{Cl}}$. This tells us it's Chlorine (Cl), it has a mass number of 37, and an atomic number of 17 (meaning 17 protons). From this, we can deduce it has $37 - 17 = 20$ neutrons. 2. Element-Mass Number Notation: $\boxed{\text{Element-A}}$ This is a simpler way to name an isotope. You state the element's full name, followed by a hyphen and its mass number. Example: For the same isotope, it would be called Chlorine-37.