STUDENT SPACE · TOPIC 2
Proton number and isotopes
Use atomic symbols to count particles and recognise isotopes.
The essentials
- Proton number Z identifies the element. Mass number A is the number of protons plus neutrons.
- Neutrons = A − Z. A neutral atom has Z electrons.
- Isotopes have the same proton number but different neutron numbers.
Key vocabulary
| English | Chinese |
|---|---|
| proton number | 质子数 |
| mass number | 质量数 |
| neutron | 中子 |
| isotope | 同位素 |
Quick practice
Two neutral atoms each have 8 protons. One has 8 neutrons and the other has 9. How are they related?
Need a hint?
Compare proton numbers first, then neutron numbers.
Check your reasoning after trying
They are isotopes of oxygen. They have the same proton number but different neutron numbers, giving mass numbers 16 and 17.
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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