Energy Shells & Subshells
Visualize how electrons are organized into energy shells and subshells. Understand the relationship between shell number, subshell types, orbital counts, and maximum electron capacity.
About this simulation
- What
- An interactive Chemistry simulation of Energy Shells & Subshells.
- Who
- Designed for AP, IB, and A‑Level Chemistry students.
- How
- Runs in any modern browser — drag, adjust, and explore in real time.
Updated 2026-04-28
Key Concepts
Energy Shells (能层)
Electrons in a multi-electron atom occupy distinct energy shells numbered 1 through 7 (K through Q). Inner shells have lower energy and are closer to the nucleus.
Subshells (能级)
Each energy shell is divided into subshells labeled s, p, d, and f, in order of increasing energy. Shell n contains exactly n types of subshells.
Orbitals and Electron Capacity
Each subshell contains a fixed number of orbitals (s=1, p=3, d=5, f=7), and each orbital holds at most 2 electrons. This determines the maximum electron capacity of each subshell.
The 2n² Rule
The maximum number of electrons in shell n is 2n². This formula emerges from summing the electron capacities of all subshells within the shell.
Understanding Energy Shells and Subshells
In a multi-electron atom, electrons do not all have the same energy. They are arranged in energy shells (also called principal energy levels), numbered 1 through 7 and labeled K through Q. The closer a shell is to the nucleus, the lower its energy.
Each energy shell is further divided into subshells (also called sublevels), labeled s, p, d, and f in order of increasing energy. The number of subshells in any shell equals the shell number n — so Shell 1 has only 1s, Shell 2 has 2s and 2p, Shell 3 has 3s, 3p, and 3d, and so on.
Each subshell contains a specific number of orbitals: s has 1, p has 3, d has 5, and f has 7. Since each orbital can hold a maximum of 2 electrons (with opposite spins), the electron capacity of each subshell is 2, 6, 10, and 14 respectively. Summing these across all subshells in a shell gives the 2n² rule for maximum electron capacity.