Summary
Electrons in an atom are arranged in energy levels or shells around the nucleus, with each shell having a specific number of electrons it can hold. Electrons occupy orbitals within these shells, following specific energy orders.
- Energy Levels — specific distances from the nucleus where electrons orbit. Example: The first energy level can hold up to 2 electrons.
- Sub-shells — divisions within energy levels that have specific energy capacities. Example: The p-sub-shell can hold up to 6 electrons.
- Orbitals — regions within an atom where electrons are likely to be found. Example: The s-orbital is spherical, while the p-orbital is dumbbell-shaped.
- Principal Quantum Number (n) — a number that describes the energy level of an electron. Example: n=1 is the closest energy level to the nucleus.
- Electronic Configuration — the arrangement of electrons in an atom's energy levels. Example: Carbon's configuration is 1s2 2s2 2p2.
Exam Tips
Key Definitions to Remember
- Energy Levels
- Sub-shells
- Orbitals
- Principal Quantum Number
- Electronic Configuration
Common Confusions
- Confusing sub-shells with orbitals
- Misunderstanding the order of filling energy levels
Typical Exam Questions
- What is the electronic configuration of carbon? 1s2 2s2 2p2
- How many electrons can the p-sub-shell hold? 6 electrons
- What shape is the s-orbital? Spherical
What Examiners Usually Test
- Understanding of electron configurations
- Ability to determine the number of electrons in sub-shells
- Knowledge of the order of filling energy levels