Electron Configuration - Shells and Subshells

Shells and Subshells

See also: Electron shell
s (=0) p (=1)
m=0 m=0 m=±1
s pz px py

Electron configuration was first conceived of under the Bohr model of the atom, and it is still common to speak of shells and subshells despite the advances in understanding of the quantum-mechanical nature of electrons.

An electron shell is the set of allowed states electrons may occupy which share the same principal quantum number, n (the number before the letter in the orbital label). An atom's nth electron shell can accommodate 2n2 electrons, e.g. the first shell can accommodate 2 electrons, the second shell 8 electrons, and the third shell 18 electrons. The factor of two arises because the allowed states are doubled due to electron spin—each atomic orbital admits up to two otherwise identical electrons with opposite spin, one with a spin +1/2 (usually noted by an up-arrow) and one with a spin −1/2 (with a down-arrow).

A subshell is the set of states defined by a common azimuthal quantum number, ℓ, within a shell. The values ℓ = 0, 1, 2, 3 correspond to the s, p, d, and f labels, respectively. The maximum number of electrons which can be placed in a subshell is given by 2(2ℓ + 1). This gives two electrons in an s subshell, six electrons in a p subshell, ten electrons in a d subshell and fourteen electrons in an f subshell.

The numbers of electrons that can occupy each shell and each subshell arise from the equations of quantum mechanics, in particular the Pauli exclusion principle, which states that no two electrons in the same atom can have the same values of the four quantum numbers.

Read more about this topic:  Electron Configuration

Famous quotes containing the words shells and and/or shells:

    Words today are like the shells and rope of seaweed which a child brings home glistening from the beach and which in an hour have lost their lustre.
    Cyril Connolly (1903–1974)

    It was the most wild and desolate region we had camped in, where, if anywhere, one might expect to meet with befitting inhabitants, but I heard only the squeak of a nighthawk flitting over. The moon in her first quarter, in the fore part of the night, setting over the bare rocky hills garnished with tall, charred, and hollow stumps or shells of trees, served to reveal the desolation.
    Henry David Thoreau (1817–1862)