Electron Configuration

Electron Configuration

1. Electrons are arranged around atoms in orbitals that have a particular shape and energy

   • These orbitals occur within energy levels and associated sublevels
     • When placing electrons in orbitals, the sublevels of lowest energy are always filled first
       • The order of energies of the first eight sublevels is: 1s2s2p3s3p4s3d4p

2. The electron configuration for any atom gives the number of electrons at each sublevel

   • The electron configuration can be written in an abbreviated form in which the inner core of electrons (those not in the outer valence shell) are represented by the corresponding inert gas configuration

3. Because all orbitals within the same sublevel of an atom have the same energy, they are filled so that as many electrons as possible remain unpaired

   • This reduces the repulsion resulting from electrons occupying the same region of space
     • A half-filled sublevel is also a particularly stable (or low energy) state
       • This explains the unusual electron configurations for the transition metals Cr and Cu, where, in each case, an electron is promoted from the slightly lower 4s level to the 3d sublevel to achieve half-filled and filled sublevels respectively
         • Cr [Ar]3d5 4s1 Cu {Ar]3d10 4s1