Isotopes and Abundance

an atom of an element with the same number of protons but a different number of neutrons.

Changing neutrons also changes the isotope’s mass number. 

Most elements have many isotopes, so each element is given an average atomic mass.

Look at the picture to the right!

There are three isotopes of the element hydrogen: protium, deuterium, and tritium.

a weighted average of the masses of an element's isotopes.

Considers the masses of the isotopes AND their percent abundance. 

describes the percent amount (how much) this isotope exists in nature.

Remember:

Every isotope is an atom of the same element

The Overall Abundance must equal 100% in order to represent all isotopes found in nature

1. Convert abundance into decimal form

2. Multiply/Combine the average atomic mass with the decimal or...

3.Average Atomic Mass =

(mass of isotope 1 X decimal abundance) + (mass of isotope 2 X decimal abundance)

DONT FORGET THE UNITS!