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In atomic physics and quantum chemistry, the Aufbau principle (/ ˈ aʊ f b aʊ /, from German: Aufbauprinzip, lit. 'building-up principle'), also called the Aufbau rule, states that in the ground state of an atom or ion, electrons first fill subshells of the lowest available energy, then fill subshells of higher energy. For example, the 1s ...
Atomic Spectroscopy, by W.C. Martin and W.L. Wiese in Atomic, Molecular, & Optical Physics Handbook, ed. by G.W.F. Drake (AIP, Woodbury, NY, 1996) Chapter 10, pp. 135–153. This website is also cited in the CRC Handbook as source of Section 1, subsection Electron Configuration of Neutral Atoms in the Ground State.
[3] As a result of Hund's rule, constraints are placed on the way atomic orbitals are filled in the ground state using the Aufbau principle. Before any two electrons occupy an orbital in a subshell, other orbitals in the same subshell must first each contain one electron. Also, the electrons filling a subshell will have parallel spin before the ...
As an example, consider the ground state of silicon. The electron configuration of Si is 1s 2 2s 2 2p 6 3s 2 3p 2 (see spectroscopic notation ). We need to consider only the outer 3p 2 electrons, for which it can be shown (see term symbols ) that the possible terms allowed by the Pauli exclusion principle are 1 D , 3 P , and 1 S .
For example, the electron configuration of the neon atom is 1s 2 2s 2 2p 6, meaning that the 1s, 2s, and 2p subshells are occupied by two, two, and six electrons, respectively. Electronic configurations describe each electron as moving independently in an orbital, in an average field created by the nuclei and all the other electrons.
The most famous example is Vaska's complex (IrCl(CO)(PPh 3) 2), [PtCl 4] 2−, and Zeise's salt [PtCl 3 (η 2-C 2 H 4)] −. In such complexes, the d z 2 orbital is doubly occupied and nonbonding. Many catalytic cycles operate via complexes that alternate between 18-electron and square-planar 16-electron configurations.
Don't rely on bloviating pundits to tell you who'll prevail on Hollywood's big night. The Huffington Post crunched the stats on every Oscar nominee of the past 30 years to produce a scientific metric for predicting the winners at the 2013 Academy Awards.
In physical chemistry: The Jahn–Teller effect – splitting of electronic levels in a molecule because breaking the symmetry lowers the energy when the degenerate orbitals are partially filled. Resonance (chemistry) leads to creation of delocalized electron states. (Feynman 1965, chapter 10, § 4)