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. It may be stated as:
- a maximum of two electrons are put into orbitals in the order of increasing orbital energy: the lowest-energy orbitals are filled before electrons are placed in higher-energy orbitals.
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). This rule was first stated by Charles Janet in 1929, rediscovered by Erwin Madelung in 1936, and later given a theoretical justification by V.M. Klechkowski
-
- Orbitals are filled in the order of increasing n+l;
- Where two orbitals have the same value of n+l, they are filled in order of increasing n.
This gives the following order for filling the orbitals:
- 1s, 2s, 2p, 3s, 3p, 4s, 3d, 4p, 5s, 4d, 5p, 6s, 4f, 5d, 6p, 7s, 5f, 6d, 7p, (8s, 5g, 6f, 7d, 8p, and 9s)
In this list the orbitals in parentheses are not occupied in the ground state of the heaviest atom now known (Uuo, Z = 118).
The Aufbau principle can be applied, in a modified form, to the protons and neutrons in the atomic nucleus, as in the shell model of nuclear physics and nuclear chemistry.
Read more about this topic: Electron Configuration
Famous quotes containing the words principle and/or rule:
“As in an icicle the agnostic abides alone. The vital principle is taken out of all endeavor for improving himself or bettering his fellows. All hope in the grand possibilities of life are blasted.”
—Anna Julia Cooper (1859–1964)
“Charity is a cop-out so traditionally female in its apparent self-effacement that there seems resonant comfort in it. We’re no longer supposed to serve the imaginations of men who have dominated us. We are to give up ourselves instead to those whose suffering is greater than our own. Looking down is just as distorting as looking up and as dangerous in perpetuating hierarchies.”
—Jane Rule (b. 1931)