STUDENT SPACE · TOPIC 3
Isotopes and relative atomic mass
Explain isotope chemistry and calculate a weighted relative atomic mass.
The essentials
- Neutral isotopes have the same electronic configuration and therefore the same chemical properties.
- Relative atomic mass is an abundance-weighted average compared with one twelfth of the mass of carbon-12. It has no unit.
- For percentage abundances, multiply each isotope mass by its abundance, add the results and divide by 100.
Key vocabulary
| English | Chinese |
|---|---|
| relative atomic mass | 相对原子质量 |
| abundance | 丰度 |
| weighted average | 加权平均值 |
| chemical properties | 化学性质 |
Quick practice
A sample contains 50% isotope-20 and 50% isotope-22. What is its relative atomic mass?
Need a hint?
Both isotopes contribute equally to the average.
Check your reasoning after trying
(20 × 50 + 22 × 50) ÷ 100 = 21. This does not mean each atom has mass number 21.
Use the matching chapter worksheet. Attempt independently, compare your reasoning with your partner, then bring unresolved questions to your teacher.
Isotopes and Atomic Mass
Change the number of neutrons and compare isotope mixtures.
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