Specification Point 1.19:
Understand how to deduce the electronic configuration of the first 20 elements from their positions in the periodic table
Deducing Electronic Configurations
Electrons move around the nucleus in different energy levels. The energy levels are called electron shells.
Electronic configuration: The arrangement of electrons into shells for an atom. This can be figured out by following some rules:
- Electrons always occupy shells that are closest to the nucleus first
- When a shell becomes full, electrons will fill the next shell
Electronic configuration of the first 20 elements:
| Element | Number of electrons | Electronic configuration |
|---|---|---|
| Hydrogen | 1 | 1 |
| Helium | 2 | 2 |
| Lithium | 3 | 2 · 1 |
| Beryllium | 4 | 2 · 2 |
| Boron | 5 | 2 · 3 |
| Carbon | 6 | 2 · 4 |
| Nitrogen | 7 | 2 · 5 |
| Oxygen | 8 | 2 · 6 |
| Fluorine | 9 | 2 · 7 |
| Neon | 10 | 2 · 8 |
| Sodium | 11 | 2 · 8 · 1 |
| Magnesium | 12 | 2 · 8 · 2 |
| Aluminium | 13 | 2 · 8 · 3 |
| Silicon | 14 | 2 · 8 · 4 |
| Phosphorus | 15 | 2 · 8 · 5 |
| Sulphur | 16 | 2 · 8 · 6 |
| Chlorine | 17 | 2 · 8 · 7 |
| Argon | 18 | 2 · 8 · 8 |
| Potassium | 19 | 2 · 8 · 8 · 1 |
| Calcium | 20 | 2 · 8 · 8 · 2 |
Specification Point 1.22:
Understand how the electronic configuration of a main group element is related to its position in the periodic table
Electronic Configuration & Periodic Table Position
Electronic configuration: The arrangement of electrons into shells for an atom (e.g electronic configuration of carbon is 2 . 4)
Electronic configuration and position in periodic table
- The number of notations in the electronic configuration will show the number of shells of electrons the atom has, showing the period
- The last notation shows the number of outer electrons the atom has, showing the group
Example: Electronic configuration of Chlorine:
Period: The red numbers at the bottom show the number of notations which is 3, showing that a chlorine atom has 3 shells of electrons
Group: The green box highlights the last notation, which is 7, showing that a chlorine atom has 7 outer electrons
The position of Chlorine on the periodic table:
Author: Jamie
Jamie got a First class degree in Chemistry from Oxford University before going on to teach chemistry full time as a professional tutor. He’s put together these handy revision notes to match the Edexcel IGCSE Chemistry specification so you can learn exactly what you need to know for your exams.