Grade 10 · Theory
Electron configuration
Atomic structure · about 3 min
Visual overview: Electron configuration1 MIN READ
2 study sections · pause after each one and recall the key ideaElectrons occupy energy levels in a set order, and the outer electrons determine bonding.
Key points- Shells fill in order: 2, 8, 8 for the first twenty elements.
- Aufbau notation fills sub-levels by increasing energy: 1s² 2s² 2p⁶ 3s² 3p⁶ 4s².
- Valence electrons are those in the outermost energy level.
- Atoms react to reach a full outer shell (the octet rule).
- Valence electrons — outer-shell electrons involved in bonding.
- Aufbau principle — fill the lowest energy sub-level first.
EXAM TIP
the group number on the periodic table gives the valence electrons for main-group elements — use it as a shortcut.