Electron Configuration

Energy –Level diagrams show the distribution of electrons down to the orbital level and at times this might be too much information. We can look at the probable distribution of electrons in an atom using its electron configuration, which shows the number of electrons, indicated by a superscript, in each sublevel. For example, a species with the electron configuration: 1s²2s²2p⁵ Has two electrons in the 1s sublevel, two electrons in the 2s sublevel, and five electrons in the 2p sublevel.

Shorthand Form of Electron Configurations

There is an internationally accepted shortcut for writing electron configurations. The core electrons of an atom are expressed by using a symbol to represent all of the electrons of the preceding noble gas. Just the remaining electrons beyond the noble gas are shown in the electron configuration. This reflects the stability of the noble gases and the theory that only the electrons beyond the noble gas (the outer shell electrons) are chemically important for explaining chemical properties.

Anomalous Electron Configurations

Electron configurations can be determined experimentally from a variety of sophisticated experimental designs. The evidence suggests that half-filled and filled subshells are more stable (lower energy) than unfilled subshells. This appears to be more important for d orbitals compared to s orbitals. The justification is that the overall energy state of the atom is lower after the promotion of the electron.