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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