Shells & orbitals

About shells & orbitals

Think of shells as regions around the nucleus where electrons are most likely to be found. These regions are like “zones” or “areas” within the atom, organized according to their energy levels.
Shells are labelled using letters (K, L, M, N, etc.) starting from the nucleus outwards. Each shell has a specific energy, with the K shell being closest to the nucleus and having the lowest energy, followed by L, M, and so on.
Imagine them as concentric circles around the nucleus, with outer shells being like bigger “orbits” further away.


Within each shell, electrons occupy specific orbitals, which are subregions of probability where an electron is most likely to be found. These orbitals are like specific “paths” or “locations” within each shell.
While the shell gives a general region, the orbital pinpoints the specific area where the electron spends most of its time.
Each shell can hold a specific number of electrons depending on its shape and energy level.

Connecting Shells and Orbitals to Energy Levels

Each shell and orbital has a unique energy level. Electrons in lower shells (closer to the nucleus) and orbitals have lower energy levels than those in higher shells and orbitals. This is because they experience a stronger attraction from the positively charged nucleus, holding them closer and requiring more energy to escape.
Electron transitions typically happen between orbitals in different shells or within the same shell but with different energy levels. When an electron absorbs energy, it jumps to a higher-energy orbital (excitation). When it releases energy, it moves to a lower-energy orbital (de-excitation).


Imagine a carbon atom with six electrons. Two electrons are in the lowest energy K shell (1s orbital). The remaining four electrons occupy the L shell, two in the lower-energy 2s orbital and two in the slightly higher-energy 2p orbitals.
When a carbon atom absorbs light, one of the electrons in the 2s orbital might get excited and jump to an empty 2p orbital, moving to a higher energy level within the same shell.

Key Points

Shells and orbitals are ways to visualize the location and energy levels of electrons around the nucleus.
Electrons occupy specific orbitals within shells, with each shell having a unique energy level.
Electron transitions involve movement between orbitals, driven by absorption or release of energy.