Electron configuration

The electron configuration is the distribution of electrons in the electron shell of an atom on different energy states or lounges ( atomic orbitals ).

The state of each electron of the shell is determined by the Bohr - Sommerfeld model of the atom and the orbital model by four quantum numbers:

According to the Pauli principle, the state must match any two electrons of an atom in all four quantum numbers. Using this principle, it can be shown that the electrons are distributed to the various allowed states and thus on the shells and subshells.

The principal quantum numbers form the shells, the angular momentum quantum numbers, the lower shells. Each cup can be filled in accordance with the restrictions of, and with a maximum of 2n ² electrons. The shells are in ascending order, starting with the core shell are denoted by capital letters: K, L, M, N, O, P, Q. .. The orbitals of the spectral lines are named according to which emits an excited electron when it is in its original orbital falls back: "sharp " ( s ) "principal " (p) " diffuse " ( d) and "fundamental" (f).

The outermost occupied shell ( valence shell ) determines the chemical behavior and is therefore relevant for the classification in the periodic table.

Filling of the shells after the construction principle

At low energies starting - - With an increasing number of electrons of the elements, the possible states are occupied. According to Hund's rule, the orbitals of equal energy are first simple, then occupied twice.

The subshells are filled in the following order (row- wise, ie by period order):

1st period: 1s 2nd period: 2s 2p 3rd period: 3s 3p 4th period: 4s 3d 4p 5th period: 5s 4d 5p 6th period: 6s 4f 5d 6p 7th Period: 7s 5f 6d ... Related to the periodic table

In the periodic table the occupation of the s orbital of a new shell corresponding to hop into a new period. Within a period, the orbitals are filled in the following order:

Notation

The electron configuration of an atom is described by the occupied sub-shells:

• The number of the shell follows the letter of the lower shell and superscript the number of electrons in the outer shell. Thus results eg for the set with 5 electrons second subshell ( l = 1 or p) of the third shell ( n = 3 or M), the notation 3p5.
• In several sub- shells, the common shell is omitted: 2s2 2p3 is from 2s2 p3.
• In a more condensed form the abbreviation of the noble gas with the next lower atomic number is enclosed in square brackets and given the lack of sub-shells of the displayed element.

As chlorine: 1s2 2s2 2p6 3s2 3p5 → [ Ne ] 3s2 3p5.

The subshells are not indicated by the Aufbau principle, but in the order of the principal quantum number; So, for example, for europium: [ Xe] 4f7 6s2.

In addition, is still the cells or even Pauling usual notation as illustrative graphical representation.