BRAINCAKEElectron Configuration
Orbitals fill in order of increasing energy.
The order of filling is:
1s 2s 2p 3s 3p 4s 3d 4p 5s 4d 5p
The 4s orbital is filled before the 3d orbital as the 3d orbital has a higher energy than the 4s orbital.
Each orbital can hold up to 2 electrons as long as they have opposite spins.
The opposite spin helps to counteract the repulsion between electrons in the same orbital. Orbitals with the same energy are occupied singly and then paired when there is no unoccupied orbital left.
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Key terms in this lesson
- Atomic number
- The number of protons in the nucleus of an atom.
- Atomic orbital
- A region in space around the nucleus where there is a 95% probability of finding an electron of a given energy.
More in Atomic Structure
- Quantum Mechanics
- Energy Levels
- Atomic Orbitals
- Order of filling orbitals
- First Ionisation Energy
- Successive Ionisation Energies
- Trends in First Ionisation Energy Across a Period
- Trends in Ionisation Energy Down A Group
All 22 lessons in Atomic Structure · All AQA AS-level Chemistry topics