The atomic masses of 204Pb (1.4 percent), 206Pb (24.1 percent), 207Pb (22.1 percent), and 208Pb (52.4 percent) are 203.973020, 205.974440, 206.975872, and 207.976627 amu, respectively. Calculate the average atomic mass of lead. The percentages in parentheses denote the relative abundances.

207 amu

Explanation:

Given data

Isotope Mass Relative abundance

²⁰⁴Pb 203.973020 amu 1.4% (0.014)

²⁰⁶Pb 205.974440 amu 24.1% (0.241)

²⁰⁷Pb 206.975872 amu 22.1% (0.221)

²⁰⁸Pb 207.976627 amu 52.4% (0.524)

We can find the average atomic mass (AM) of an element using the following expression.

AM = ∑mi * abi

where

mi is the mass of each isotope

abi is the relative abundance of each isotope

AM = 203.973020 amu * 0.014 + 205.974440 amu * 0.241 + 206.975872 amu * 0.221 + 207.976627 amu * 0.524

AM = 207 amu

207amu

Explanation:

To calculate the average atomic mass of an element you must multiply the masses of its isotopes with the percent abundance divided by 100. Then you add them together for your answer.

203.973020amu * 0.014 = 2.9amu

205.974440amu * 0.241 = 49.6amu

206.975872amu * 0.221 = 45.7amu

207.976627amu * 0.524 = 109amu

2.9 + 49.6 + 45.7 + 109 = 207amu