Lesson: Relative Atomic Masses and Isotopic Abundance

In this lesson, we will learn how to calculate the relative atomic masses of elements based on the relative abundance of their isotopes.

Worksheet: 2 Questions

Q1:

A sample of lithium contains a mixture of and isotopes with atomic masses 6.01512 u and 7.01600 u respectively. The sample is by mass.

Calculate, to 3 significant figures, the average atomic mass of the sample.

A second sample of lithium also contains a mixture of and but displays a higher abundance of . How does the average atomic mass of this sample compare with that of the first?

Q2:

Protons and neutrons have masses of approximately 1 atomic mass unit (u) and cannot easily be split into smaller particles. Magnesium consists of protons, neutrons, and electrons and has a relative atomic mass of 24.3 u. Why is the relative atomic mass of magnesium significantly greater than 24 u?

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