Question

An element consists of 1.40% of an isotope with mass 203.973 u, 24.10% of an isotope with mass 205.9745 u, 22.10% of an isotope with mass 206.9759 u, and 52.40% of an isotope with mass 207.9766 u. Calculate the average atomic mass, and identify the element.

Answer 1

Answer:

Lead with an average atomic mass of 207.2.

Explanation:

To calculate the average atomic mass using isotopes we must multiply each of the masses by their percent abundances divided by 100. We must then add these values together to get the average atomic mass.

203.973u × 0.0140 = 2.86u

205.9745u × 0.2410 = 49.64u

206.9759u × 0.2210 = 45.74u

207.9766u × 0.5240 = 109.0u

109.0 + 45.74 + 49.64 + 2.86 = 207.2u

To identify the element we must check the periodic table for an element with our calculated average atomic mass.

Lead (Pb) has an average atomic mass of 207.2u.