Quantum Shells

Electrons exist in well-defined energy levels called quantum shells. Each electron is in a quantum shell which has a principal quantum number n = 1, 2, 3, 4, 5, 6, 7. The electrons in the same quantum shell have similar but not identical energies.The first shell n = 1 is closest to the nucleus. Each shell is then sub-divided into one or more sub-shells: s p d or f.The first quantum shell has only one sub-shell 1s.The second quantum shell has 2s and 2p subshells.The third quantum shell has 3s, 3p and 3d subshells.The fourth quantum shell is divided into 4s, 4p, 4d and 4f subshells.Each sub-shell has one or more orbitals:The s sub-shell has 1 orbitalThe p sub-shell has 3 orbitalsthe d sub-shell has 5 orbitalsThe f sub-shell has 7 orbitals