Percent abundance is the percentage of all the different isotopes of an element and is used to calculate the average atomic mass. For example 99.98% of all Hydrogen in the universe is [tex]^1H[/tex] meaning hydrogen with 1 proton and 0 neutrons while the remaining 0.02% is [tex]^2H[/tex] meaning that [tex]^1H[/tex] is the most abundant by percent.
