A simple electron shell diagram of lithium-7
In atomic physics and quantum chemistry, the electron configuration is the distribution of electrons of an atom or molecule (or other physical structure) in atomic or molecular orbitals.[1] For example, the electron configuration of the neon atom is 1s2...
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Electron atomic and molecular orbitals
A simple electron shell diagram of lithium-7
In atomic physics and quantum chemistry, the electron configuration is the distribution
of electrons of an atom or molecule (or other physical structure) in atomic or molecular
orbitals.[1] For example, the electron configuration of the neon atom is 1s2 2s2 2p6.
According to the laws of quantum mechanics, an energy is associated with each electron
configuration and, upon certain conditions, electrons are able to move from one orbital to
another by emission or absorption of a quantum of energy, in the form of a photon.
Knowledge of the electron configuration of different atoms is useful in understanding the
structure of the periodic table of elements. The concept is also useful for describing the
chemical bonds that hold atoms together. In bulk materials this same idea helps explain
the peculiar properties of lasers and semiconductors.
, Contents
[hide]
• 1 Shells and subshells
• 2 Notation
• 3 Energy — ground state and excited states
• 4 History
• 5 Aufbau principle and Madelung rule
o 5.1 Periodic table
o 5.2 Shortcomings of the Aufbau principle
o 5.3 Ionization of the transition metals
o 5.4 Other exceptions to Madelung's rule
• 6 Electron configuration in molecules
o 6.1 Electron configuration in solids
• 7 Applications
• 8 See also
• 9 Notes
• 10 References
• 11 External links
[edit] Shells and subshells
See also: Electron shell
s (l=0) p (l=1)
m=0 m=0 m=±1
s pz px py
n=1
n=2
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
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