This worked example covers Worked Examples: Writing Electronic Configurations 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 6 of 12 in this topic. Treat this as a marking guide for what examiners are looking for, not just a fact list.
🧮 Worked Examples: Writing Electronic Configurations
Example 1: Magnesium (Mg) — Atomic number 12
→ Fill 1st shell: 2 electrons (remaining: 10)
→ Fill 2nd shell: 8 electrons (remaining: 2)
→ Fill 3rd shell: 2 electrons
Configuration: 2,8,2
Example 2: Oxygen (O) — Atomic number 8
→ Fill 1st shell: 2 electrons (remaining: 6)
→ Fill 2nd shell: 6 electrons
Configuration: 2,6
Example 3: Potassium (K) — Atomic number 19
→ Fill 1st shell: 2 electrons (remaining: 17)
→ Fill 2nd shell: 8 electrons (remaining: 9)
→ Fill 3rd shell: 8 electrons (remaining: 1)
→ Fill 4th shell: 1 electron
Configuration: 2,8,8,1
Quick Check: An element has electronic configuration 2,8,3. Which group and period is it in, and what is its atomic number?
Group 3 (3 outer electrons), Period 3 (3 shells). Atomic number = 2 + 8 + 3 = 13 (this is aluminium, Al).
Practice questions for Electronic Configuration
What is the maximum number of electrons the first electron shell can hold?
Explain why noble gases are unreactive.