The Investigating Isotopes Activity provides 5 sets of cards (which can be printed, laminated, and easily reused year to year if desired).
Each card set contains an element with it's isotopes. For example, card set #1 contains 2 Boron Isotopes with a mass of 11 and 8 Boron Isotopes with a mass of 10. The WS guides students through first determining the number of proton, neutrons, and mass of each isotope, then determining the percentage of each mass, and finally calculating the average mass. Each problem is slightly different to both challenge students and provide variety.
An "Isotopes & Average Atomic Mass" WS is also included for use as extra practice in class or as HW.