Final answer:
To calculate the natural percentage abundance of isotopes, convert percentage abundances to decimals, then multiply each by its atomic mass number, and sum these products to get the weighted average atomic mass of the element.
Step-by-step explanation:
To find the natural percentage abundance of isotopes, you need to know the atomic masses of the isotopes and the average atomic mass of the element. Let's take chlorine as an example. Chlorine has two major isotopes, chlorine-35 and chlorine-37. The average atomic mass of chlorine is a weighted average based on the natural abundance of each isotope.
Suppose chlorine-35 has a natural abundance of 75.77%, and chlorine-37 has the remaining 24.23%. To calculate the weighted average atomic mass, you would first convert the percentages to decimals: 0.7577 for chlorine-35 and 0.2423 for chlorine-37. Then, multiply the decimal abundance by the mass number of each isotope:
- (0.7577 × 35) = 26.51 for chlorine-35
- (0.2423 × 37) = 8.965 for chlorine-37
Add these results together to get the weighted average atomic mass: (26.51 + 8.965) = 35.48 u, which is very close to the value listed on the periodic table for chlorine.
The process of calculating atomic mass takes into account the relative abundance of each isotope and its respective mass, resulting in a weighted average.