Now practice calculating average atomic mass.

The first problem will give you step by step hints. What is the average atomic mass of nitrogen? Click on the blanks to check your answers.

 mass number exact weight percent abundance 14 14.003074 99.63 15 15.000108 0.37

Change the percent abundance of nitrogen 14 to a decimal. __________

Change the percent abundance of nitrogen 15 to a decimal. __________

Plug exact weights and percentages abundance into the following equation:

(exact weight of isotope 1 x percent abundance of isotope 1) + (exact weight of isotope 2 x percent abundance of isotope 2)
= average atomic mass

(__________ x __________) + ( __________ x __________)
__________ + __________ =
__________ amu

Now calculate the following on your own.

Chlorine

 mass number exact weight percent abundance 35 34.968852 75.77 37 36.965903 24.23 The answer for chlorine: Interactive button. Assistance may be required. __________ 35.453

Magnesium

 mass number exact weight percent abundance 24 23.985042 78.99 25 24.985837 10.00 26 25.982593 11.01 The answer for magnesium: Interactive button. Assistance may be required. __________ 24.305