Electronic Energy Levels:

• The primary energy level (the average radial distance of the electron from the nucleus) is a shell, n.

  • The lowest possible energy level is the ground state with n = 1.

• n also gives the number of nodes in each of the orbitals in that shell, with one node at infinity, where:

  • A node is a region of zero probability of finding an electron.

• Nodes can have two general geometries:

  • radial (or spherical, describing a spherical shell at a specific radial distance from the nucleus). Each atom has at least one radial (spherical) node at infinity;

  • angular (either planar, e.g. as in the planar p-node and diagonal d-nodes, or cone shaped, e.g. as in the cone-shaped nodes of the d_z² orbitals which results in the donut shaped orbitals).

• Shells with n > 1 may have subshells which are different geometrical patterns of electron distribution. Thus:

  • The lowest energy pattern is spherical and given the designation s.

  • The next lowest energy distribution is bi-lobed with a planar symmetry. It is given the designation p.

  • The third lowest energy distribution has diagonal planes of symmetry and is designated d.

  • The fourth lowest energy distribution is designated f. This is the highest subshell type occupied by ground state electrons in any atom. (an infinite number of subshells exist in theory for excited states, but they are not important to our understanding).

• The average energies of the different subshells are the energy of the shell, thus when subshells are present the energy of the shell is split. For example, in the n=2 shell the 2s orbital becomes lower in energy than the shell, while the 2p orbitals become higher in energy.

• The regions of electron occupancy in subshells are called orbitals.

  • For each shell there is one s orbital.

Atomic Orbitals Supplement More orbitals and some additional explanations.

© R A Paselk 2009

Last modified 13 March 2013