# What does the superscript of an isotope notation mean?

May 6, 2018

This represents the NUMBER of nuclear particles....

#### Explanation:

Let's take a simple example, i.e. for hydrogen, the MOST abundant element in this universe. Most hydrogen nuclei contain the ONE nuclear particle, i.e. one proton....and we would represent this ISOTOPE as ""^1H, $\text{protium}$, to reflect its mass.

A smaller percentage of hydrogen atom necessarily contain the DEFINING proton, and ALSO a neutron...to give the $\text{deuterium isotope}$....i.e. ""^2H..here in the nucleus there are one proton (necessarily) and ALSO ONE neutron.

And an even smaller percentage of hydrogen atoms, contain the $\text{tritium isotope}$, i.e. ""^3H. How many neutrons does this isotope contain?

And so the superscripted number is the number of $\text{nucular particles}$, protons, and neutrons. The atomic symbol defines $Z$, the atomic number. To a first approximation (which does not work so well for hydrogen), the chemistry of the isotopes are identical.