subshell
Summary
A subshell is the set of orbitals within a shell that share the same n and l, labeled s, p, d or f (such as 2p or 3d). A full s, p, d or f subshell holds 2, 6, 10 or 14 electrons, since it has 2l + 1 orbitals with two electrons each.
Detail
Meaning: A shell is the set of orbitals with the same principal quantum number n. A subshell is the group of orbitals in that shell that also share the same angular momentum quantum number l: s (l = 0), p (l = 1), d (l = 2), f (l = 3). Shell n contains n subshells. In multielectron atoms, shielding and electron repulsion split the subshells of one shell in energy (ns < np < nd < nf), which is why 4s fills before 3d.
Equation: Orbitals in a subshell = 2l + 1, so electrons in a full subshell = 2(2l + 1). Here l is the angular momentum quantum number (dimensionless, integers from 0 to n − 1). The counts are pure numbers with no SI unit.
On the MCAT: Expect questions that ask you to write an electron configuration, count the electrons in a subshell, or decide whether a set of quantum numbers is allowed. Subshells such as 2d or 3f cannot exist, because l must be less than n. Transition metal cations lose their ns electrons before their (n − 1)d electrons.
Common confusion: A subshell is not an orbital. The 2p subshell contains three orbitals and holds up to six electrons. Also, subshells of the same shell differ in energy only in multielectron atoms. In the one-electron hydrogen atom, at MCAT level, energy depends on n alone.
Sources
- Chemistry: The Central Science
- Chemistry: A Molecular Approach
- Chemistry (Zumdahl)
Written for the MCAT and checked before it was published. For study reference only. Spotted an error? Let us know.