STUDENT SPACE · TOPIC 4
Electron shells and ions
Write electronic configurations for atoms and ions of the first 20 elements.
The essentials
- Count electrons before filling shells. Use the first-20-elements pattern where appropriate.
- Positive ions form by losing electrons; negative ions form by gaining electrons. The nucleus stays unchanged.
- Check charge using number of protons minus number of electrons.
Key vocabulary
| English | Chinese |
|---|---|
| electron shell | 电子层 |
| electronic configuration | 电子排布 |
| cation | 阳离子 |
| anion | 阴离子 |
Quick practice
An atom has 3 protons and 3 electrons. It loses one electron. State its charge and remaining electron count.
Need a hint?
The proton number stays the same.
Check your reasoning after trying
It has 2 electrons and charge 1+, because 3 − 2 = +1.
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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