Final answer:
To find the weighted average atomic mass of an element, multiply each isotope's mass by its relative abundance (in decimal form) and sum the results. This number is then compared with atomic masses on the periodic table to identify the element.
Step-by-step explanation:
To calculate the weighted average atomic mass of an element with three isotopes, you must use the percentage abundances and the isotopic masses. The formula for calculating the weighted average is to multiply each isotope's mass by its relative abundance (converted to decimal form), summing these products, and then averaging the total.
Given the isotopes have abundances and masses of 90.92% with 19.99 amu, 0.26% with 20.99 amu, and 8.82% with 21.99 amu, the calculation would be as follows:
- (0.9092 × 19.99 amu) + (0.0026 × 20.99 amu) + (0.0882 × 21.99 amu)
- = 18.099268 amu + 0.054574 amu + 1.939818 amu
- = 20.09366 amu
To identify the element, you compare your calculated average atomic mass with the atomic masses on the periodic table. The element closest to your calculated atomic mass is likely your element.