Shells and Orbitals (AQA A-Level Chemistry): Revision Notes

1.1.4 Shells and Orbitals

Principal Energy Levels

• Level 1: Holds a maximum of 2 electrons in a single 1s orbital.
• Level 2: Consists of 2s and 2p orbitals. The 2s orbital can hold 2 electrons, and the 2p orbitals can hold a maximum of 6 electrons (2 in each of the 3 p orbitals).
• Level 3: Contains 3s, 3p, and 3d orbitals. The 3d sub-level can hold 10 electrons.
• Level 4: Expands to include 4s, 4p, 4d, and 4f orbitals. Each energy level contains one or more sub-levels, which correspond to different types of orbitals: s, p, d, and f.

Energy Level Overlap

As energy levels increase, the orbitals begin to overlap. For example, the 4s orbital is of lower energy than the 3d orbital, which is why electrons fill the 4s orbital before the 3d orbital.

Types of Orbitals

• s-orbitals: Spherical in shape. Each s-orbital can hold a maximum of 2 electrons.
• p-orbitals: Dumbbell-shaped, arranged in three different orientations (x, y, z). Each can hold 2 electrons, with a total of 6 electrons in a full set.
• d-orbitals: More complex in shape, arranged in five different orientations, each holding 2 electrons, making a total of 10 electrons in a full set.
• f-orbitals: Even more complex shapes and can hold 14 electrons in total (7 orientations, each holding 2 electrons).