This is where it all connects!
- Group number = Number of electrons in the outer shell
- Period number = Number of occupied shells
Examples:
- Sodium (Na) — Configuration: 2,8,1 → Group 1 (1 outer electron), Period 3 (3 shells)
- Chlorine (Cl) — Configuration: 2,8,7 → Group 7 (7 outer electrons), Period 3 (3 shells)
- Carbon (C) — Configuration: 2,4 → Group 4 (4 outer electrons), Period 2 (2 shells)
- Neon (Ne) — Configuration: 2,8 → Group 0 (full outer shell), Period 2 (2 shells)
Why outer electrons matter:
- Atoms with the same number of outer electrons have similar chemical properties
- This is why elements in the same group behave similarly!
- Atoms with full outer shells are very stable and unreactive (noble gases)
Quick Check: Chlorine has atomic number 17. Write its electronic configuration and state which group and period it belongs to.
Configuration: 2,8,7. Group 7 (7 outer electrons). Period 3 (3 occupied shells).
This key facts covers Electronic Configuration and the Periodic Table within Electronic Configuration for GCSE Chemistry. Revise Electronic Configuration in Atomic Structure for GCSE Chemistry with 24 exam-style questions and 24 flashcards. Use this page as part of a wider topic revision path rather than treating it as an isolated fact. It is section 5 of 12 in this topic. Use this key facts to connect the idea to the wider topic before moving on to questions and flashcards.
Practice questions for Electronic Configuration
What is the maximum number of electrons the first electron shell can hold?
Explain why noble gases are unreactive.