Naturally occurring lead exists as four stable isotopes: ^204 Pb with a mass of 203.973 amu(1.

step 1 So to calculate the average atomic mass, we want to take the mass of each isotope and multiply i

Naturally occurring lead exists as four stable isotopes: ...

Naturally occurring lead exists as four stable isotopes: ${ }^{204} \mathrm{~Pb}$ with a mass of $203.973 \mathrm{amu}\left(1.480 \%\right.$ ); ${ }^{206} \mathrm{~Pb}$, $205.974 \mathrm{amu}(23.60 \%)$; ${ }^{207} \mathrm{~Pb}, 206.9759 \mathrm{amu}(22.60 \%$ ); and ${ }^{208} \mathrm{~Pb}, 207.9766 \mathrm{amu}(52.30 \%)$. Calculate the average atomic mass of lead.

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Key Concepts

Stable Isotopes

Stable isotopes are forms of an element that have the same number of protons but different numbers of neutrons, and do not undergo radioactive decay over time. Their existence allows naturally occurring elements to have a range of atomic masses, which are reflected in the measured average atomic masses of those elements.

Isotopic Abundance

Isotopic abundance refers to the relative percentage or proportion of each isotope found naturally in a sample of an element. These percentages are crucial because they determine the contribution of each isotope’s mass to the overall average atomic mass of the element.

Weighted Average Calculation

The weighted average calculation in the context of atomic mass involves multiplying the mass of each isotope by its respective abundance (expressed as a fraction), and then summing these products. This method results in the average atomic mass, which represents the effective mass of an atom of the element as it occurs naturally.

Atomic Mass Unit

The atomic mass unit (amu) is a standardized unit of mass used to express the mass of atoms and subatomic particles. It is defined as one twelfth of the mass of a carbon-12 atom, providing a convenient scale for quantifying atomic and molecular masses in chemical calculations.

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