Chemistry

Electron configurations

Ground state electron configurations of atoms show the populations of orbitals in atoms. For example, the ground state electron configuration of boron (Z = 5) is 1s²2s²2p¹. With respect to assigning electrons to degenerate p orbitals, Hund's rule applies, so the electron configuration of nitrogen (Z = 7) is 1s²2s²2p_x¹2p_y¹2p_z¹. A further condensation of the shorthand notation for electron configurations applies whereby the core and valence electrons are separated. For example, the electron configuration of aluminium (Z = 13) is 1s²2s²2p⁶3s²3p¹ and 1s²2s²2p⁶ is the electronic configuration of neon, so that of aluminium in condensed form is [Ne]3s²3p¹. Similarly, the condensed form of the electron configuration of bromine (Z = 35) is [Ar]4s²4p⁵.

Exceptions to the order of orbital filling are found in the transition metals, lanthanoids and actinoids, where d and f orbitals, respectively, are involved. See pages 143–144 of the textbook for these.