1. Average Atomic Mass If there are 2 naturally occurring isotopes of Neon including Ne-20 and Ne-22. then the average mass of Neon atoms should be ___ amu. Calculated as a weighted average of atoms in a sample of naturally occurring isotopes. Why does the PT lists it as 20.18 amu?

2. A weighted average atomic mass is calculated from both the masses of each isotope and the relative abundance (%) of each isotope. 63 Cu is 69% abundant 65 Cu is 31% abundant To which will the average mass be closer, 63 or 65? Average Atomic Mass

3. copper-63 has a mass of 62.93 amu and natural abundance of 69.15% copper-65 has a mass of 64.93 amu and has a natural abundance of 30.85% = (62.93)(0.6915) + (64.93)(0.3085) = 63.55 Avg. Mass = (Mass 1 )(%) + (Mass 2 )(%) … Calculating Average Atomic Mass

4. because… the weighted average atomic mass of neon from the PT is 20.18 amu. neon-20neon-22 Which isotope is in greater relative abundance in natural samples of neon?

5. 1. If an unusually selected sample of sulfur contained 90.0% sulfur-32 and 10.0% sulfur-34, what would be its average atomic mass? A. 32.2 amu B. 32.9 amu C. 33.5 amu D. 34.2 amu Quick Quiz! = (32)(0.900) + (34)(0.100) = 32.2 Avg. = (M 1 )(%) + (M 2 )(%)