Aufbau Principle

The Aufbau principle (from the German Aufbau meaning "building up, construction": also Aufbau rule or building-up principle) is used to determine the electron configuration of an atom, molecule or ion. The principle postulates a hypothetical process in which an atom is "built up" by progressively adding electrons. As they are added, they assume their most stable conditions (electron orbitals) with respect to the nucleus and those electrons already there.

According to the principle, electrons fill orbitals starting at the lowest available (possible) energy states before filling higher states (e.g. 1s before 2s). The number of electrons that can occupy each orbital is limited by the Pauli exclusion principle. If multiple orbitals of the same energy are available, Hund's rule states that unoccupied orbitals will be filled before occupied orbitals are reused (by electrons having different spins).

A version of the Aufbau principle can also be used to predict the configuration of protons and neutrons in an atomic nucleus.

Read more about Aufbau PrincipleThe Madelung Energy Ordering Rule

Other articles related to "aufbau, aufbau principle, principle":

Rudolf Carnap - Life and Work
... Structure of the World (German "Der logische Aufbau der Welt"), in which he developed a rigorous formal version of empiricism, defining all scientific terms in phenomenalistic terms ... The formal system of the Aufbau (as the work is commonly termed) was grounded in a single primitive dyadic predicate, which is satisfied if "two" individuals "resemble" each other ... The Aufbau was greatly influenced by Principia Mathematica, and warrants comparison with the mereotopological metaphysics A ...
Transition Metal - Classification
... This is based on the aufbau principle (or Madelung rule) for filling electron subshells, in which 4f is filled before 5d (and 5f before 6d), so that the f subshell is actually ... However La and Ac are exceptions to the Aufbau principle with electron configuration s2d1 (not s2f1 as the aufbau principle predicts) so it is not clear from atomic electron configurations whether La or Lu (Ac or Lr ...
Electron Configuration - Aufbau Principle and Madelung Rule
... The Aufbau principle (from the German Aufbau, "building up, construction") was an important part of Bohr's original concept of electron configuration ... The principle works very well (for the ground states of the atoms) for the first 18 elements, then decreasingly well for the following 100 elements ... The modern form of the Aufbau principle describes an order of orbital energies given by Madelung's rule (or Klechkowski's rule) ...
Electron Configuration - Aufbau Principle and Madelung Rule - Shortcomings of The Aufbau Principle
... The Aufbau principle rests on a fundamental postulate that the order of orbital energies is fixed, both for a given element and between different elements neither of ... The fact that the Aufbau principle is based on an approximation can be seen from the fact that there is an almost-fixed filling order at all, that, within a ...

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