In chemistry and atomic physics, an electron shell, or a principal energy level, may be thought of as an orbit followed by electrons around an atom's nucleus. read more
Definition: A subshell is a subdivision of electron shells separated by electron orbitals. Subshells are labelled s, p, d, and f in an electron configuration. Examples: The first electron shell is the 1s subshell. The second shell of electrons contains the 2s and 2p subshells. read more