Atomic Mass

What is atomic mass?

The atomic mass of an element is a weighted average mass of the atoms in a naturally occurring sample of the element.

• Average Atomic Mass

What is an isotope of an element?

Isotopes are atoms that have the same number of protons but a different number of neutrons than other atoms of the same element.    Because isotopes of an element have different numbers of neutrons, they also have different mass numbers. They DO have the same atomic number, however.    

• Average Atomic Mass

What is natural abundance?

Natural abundance is the relative amount of a certain isotope of an element out of 1. It can be described as a decimal or as a percent.     

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Caption: : For example, above are the natural abundances of the two isotopes of chlorine as percents. They add up to 100%.

How do you calculate atomic mass?

To calculate: 1. Multiply the mass of each individual isotope by its natural abundance (expressed as a decimal) 2. Add the products   This will give the percent of the element taken up by each isotope out of 1.    Example -------->

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