Electronic Configuration of Elements
Chemistry: Cambridge International GCSE Supplement, topic 2.2.3
Electronic Configuration of Elements and the Periodic Table
Electronic configuration shows electron shells (e.g. 2,8,8). Groups are outer electrons, and periods are shells. Noble gases have full outer shells, making them stable.
What is electronic configuration?
- Electronic configuration shows how electrons arrange in shells around an atom's nucleus.
- Each shell holds a certain number of electrons: 2 in the first, 8 in the second, and 8 in the third for elements 1-20.
- The number of protons (atomic number) equals the number of electrons in a neutral atom.
Writing electronic configurations for elements 1-20
- Start filling electrons from the innermost shell outward.
- Example for Oxygen (8): 2 electrons in shell 1, and 6 electrons in shell 2 (2,6).
- Example for Calcium (20): Shell 1 has 2, shell 2 has 8, shell 3 has 8, shell 4 has 2 (2,8,8,2).
- Write numbers separated by commas to show electrons in each shell.
Group and period numbers link to electron shells
- Group number (I to VII) equals the number of electrons in the outer shell for these groups.
- Period number equals the number of shells occupied by electrons.
- Example: Sodium is in Group I and Period 3, so it has 1 electron in its outer shell and 3 electron shells.
Electronic configuration of ions
- Ions form when atoms gain or lose electrons to become charged.
- Write the electronic configuration of an ion based on its new number of electrons.
- Example: Na+ ion loses 1 electron, so configuration of Na+ is 2,8.
- Example: O2- ion gains 2 electrons, so configuration is 2,8.
Noble gases have full outer shells
- Group VIII (18) are the Noble Gases.
- These gases have full outer electron shells, making them very stable.
- Examples: Helium (2 electrons) and Neon (2,8) have full outer shells.
- This stability explains why Noble Gases do not easily form ions or react.
Test yourself on Electronic Configuration of Elements
What does the electronic configuration describe?