Sublevels and Atomic Orbitals

Specification Reference S1.3.4

Quick Notes:

Each main energy level (n) is divided into sublevels: s, p, d, and f.
These sublevels have different energies and hold different numbers of electrons:
- s: 1 orbital → 2 electrons
- p: 3 orbitals → 6 electrons
- d: 5 orbitals → 10 electrons
- f: 7 orbitals → 14 electrons
s orbitals are spherical in shape.
p orbitals have a dumbbell shape and exist in three orientations: p_x, p_y, p_z (at right angles in 3D space).

IB Chemistry diagram of atomic orbital shapes showing spherical s orbital and dumbbell-shaped p orbitals in three orientations.

Understanding orbital shapes helps explain bonding and molecular shape later in the course.

Full Notes:

Sublevels

The model of the atom becomes more accurate when we divide each main energy level (n) into sublevels:

These are labelled s, p, d, and f, and they differ in both energy and shape.

Not all sublevels are present in each energy level:

n = 1 has only s
n = 2 has s and p
n = 3 has s, p and d
n = 4 has s, p, d and f

Each sublevel contains one or more atomic orbitals – regions of space where electrons are most likely to be found.

s and p Orbitals

s-orbital

Each s sublevel contains one s orbital.
The shape of an s orbital is spherical.
The orbital is symmetrical around the nucleus.
Can hold a maximum of 2 electrons.

p-orbitals

Each p sublevel contains three p orbitals.
These are labelled p_x, p_y, and p_z – each aligned along a different axis in 3D space.
The shape of a p orbital is dumbbell-shaped (like two balloons tied at the nucleus).
Each p orbital can hold 2 electrons, so the whole p sublevel holds 6 electrons total.

Summary of Orbitals by Sublevel

Sublevel	Number of Orbitals	Maximum Electrons
s	1	2
p	3	6
d	5	10
f	7	14

For IB at this stage, you only need to recognise the shape and orientation of s and p orbitals.

Summary

Main energy levels divide into s, p, d, and f sublevels.
s orbitals are spherical; p orbitals are dumbbell-shaped.
Electron capacity is 2 in s, 6 in p, 10 in d, and 14 in f sublevels.
This model explains electron arrangements and bonding patterns in chemistry.

Linked Questions

Structure 3.1 – Linked Course Question

What is the relationship between energy sublevels and the block nature of the periodic table?

The block to which an element belongs in the periodic table is determined by the type of atomic orbital being filled by its outermost electrons. Elements filling s orbitals form the s-block (Groups 1–2), those filling p orbitals form the p-block (Groups 13–18), transition metals filling d orbitals form the d-block, and lanthanides and actinides filling f orbitals make up the f-block. This organisation reflects the underlying quantum structure of atoms and explains recurring patterns in chemical and physical properties across the table.