The electron configuration describes the arrangement of electrons in an atom.
The electron configuration of an element determines the chemical and physical behavior of that element.
There are three rules or regularities for arriving at a predicted electron configuration [local] of an element.
Using these gives a pattern to follow to assign electrons to orbitals. There are exceptions.. You can follow the three major rules for electron configurations in this simulation. The following diagram is a handy one for helping students learn the general order of orbital filling and to assist in writing electron configurations.
Check a configuration.
Follow the arrows from the blunt end of the top arrow to the point, continuing to the next lowest arrow. The general order of subshell filling is revealed. This table is easy to recreate since all orbitals of the same energy are on the same horizontal row.
When the quantum mechanical model is applied to hydrogen, Schrodinger's equation can be solved exactly. Elements with more than one electron introduce problems associated with the potential energy of the repulsion between electrons. Since these electron repulsions can't be determined exactly a problem termed the electron correlation problem exists.
When working with atoms with more than one electron, approximations are made and the orbitals that result are termed "hydrogen-like." They are similar in shape but their sizes and energies are different than those of hydrogen.
In a one electron system, like hydrogen, all the orbitals at the same value of n have the same energy; they are termed degenerate. Do not confuse the meaning of degenerate as used with orbitals, with the common meaning of this term. In a system with more electrons there will be small differences between the s, p, d, and f orbitals of the same n value. The order of filling shown above is based on the pattern of orbitals in a many electron atom.
There are several ways to represent electron configurations.
P, 1s2 2s2 2p6 3s2 3p3
P, 1s2 2s2 2p6 3s2 3px1 3py1 3pz1
P, [Ne] 3s2 3p3
A shortcut in writing electron configurations starts with the symbol of the previous Noble Gas in square brackets followed by the orbitals filled by the remaining electrons. For example, the electron configuration of Scandium (21) would be written [Ar]4s2 3d1.
