CAIE IGCSE Chemistry Group Period and Electron Shell Rules
Practise using electronic configurations to infer an element's group and period and recognising noble gases by their complete outer electron shells.
- Syllabus
- 2026–2028
- Course
- Chemistry 0620
Practise using electronic configurations to infer an element's group and period and recognising noble gases by their complete outer electron shells.
The symbols of the elements of Period 3 of the Periodic Table are shown.

Answer the following questions about these elements.
Each element may be used once, more than once or not at all.
Write the symbol of an element which:
has only two electrons in its outermost shell
Mg