Name _________________________________________________________________ Hour __________________ Isotopes of m&m-ium Elements commonly exist with differing numbers of neutrons. We call these elements isotopes and an example is Bromine-79 and Bromine-81. These isotopes are naturally occurring…but do not exist equally in nature. Br-79 is more common and occurs 55% of the time while Br-81 occurs 45% of the time. To calculate the average atomic mass (the weighted average of the masses of its isotopes) of bromine you need to take into account the relative abundance of each element. The average atomic mass = (% abundance of isotope 1)x(mass of isotope 1) + (% abundance of isotope 2)x(mass of isotope 2) (% should be expressed in decimals) Pre-Lab Questions: 1. Calculate the average atomic mass of Bromine using the % abundances above: 2. Carbon has 2 stable isotopes: C-12 with a natural abundance of 98.89% and C-14 at 1.11%. Calculate the average atomic mass of Carbon. m&mium, a recently discovered element from the chocolate mountains of Wonkaland, exits as two isotopes. m&mium has many different colors and your job is to find the average atomic mass of one color of m&mium. Safety Precautions: Never eat anything that has touched lab equipment! Use a baking cup so your group can eat the m&ms when you are done! Procedure: Show all work for all calculations. 1. Record the number of small m&m’s and large m&m’s you have (your color only) in the table. 2. Record the total number of m&m’s you have. 3. Find the percent of your m&m’s that are small and large. 4. Find the mass of all small m&m’s. Find the average mass of a small m&m. 5. Find the mass of all large m&m’s. Find the average mass of a large m&m. 6. Calculate the average atomic mass of your color of m&m. Data: Type of m&m Amount % abundance Mass of each Average mass Large Small __________ TOTAL # of all m&m’s The average atomic mass of my color of m&mium is: Name _________________________________________________________________ Hour __________________ Questions 1. How does your average atomic mass compare to that of another color? (Ask someone from a different lab group.) 2. Why is it important to use the average mass of all small m&m’s rather than just the mass of one small m&m? 3. Which type of m&m (small or large) represents the heavier isotope of m&mium? 4. Which type of m&m (small or large) is more abundant in your sample? 5. Which type of m&m (small or large) would you predict to be a more stable isotope? Why? 6. What two subatomic particles give the atom almost all of its mass? 7. In which part of the atom is most of the mass located? 8. Which subatomic particle is responsible for all the reacting an element does? 9. A newly discovered element, Benedictium was found to have several isotopes with the following abundance: 22.2% Benedictium-227, 17.9% Benedictium-239, 31.4% Benedictium-251 and 28.5% Benedictium-265. What is the average atomic mass of Benedictium? Conclusion: Write a brief, but well written conclusion that incorporates what an isotope is, how to calculate the average atomic mass of an element, and what you know about the structure of an atom. .