1.3.2—Number of orbitals making up s, p and d

A sub-shell is made of atomic orbitals: an s sub-shell contains 1 orbital, a p sub-shell contains 3 orbitals, and a d sub-shell contains 5 orbitals. The three p orbitals are conventionally labelled pₓ, pᵧ and p_z.

Each orbital can hold a maximum of 2 electrons. Therefore the corresponding sub-shell capacities are s = 1 × 2 = 2 electrons, p = 3 × 2 = 6 electrons and d = 5 × 2 = 10 electrons. Where included, f has 7 orbitals and a capacity of 14 electrons.

To determine a sub-shell capacity, identify its orbital count and multiply by two. In a ground-state p sub-shell, orbitals of the same sub-shell have equal energy; electrons occupy separate orbitals before pairing, subject to the electron-configuration rules.

Do not confuse the number of orbitals with the number of electrons, and do not infer a new shell from the s/p/d label alone. Detailed filling sequences, ions and exceptions belong to the neighbouring electron-configuration objective; detailed d-orbital shape is not required at AS Level.