Orbital+energy

In atoms with a single electron (hydrogen-like atoms), the energy of an orbital (and, consequently, of any electrons in the orbital) is determined exclusively by. The orbital has the lowest possible energy in the atom. Each successively higher value of has a higher level of energy, but the difference decreases as  increases. For high, the level of energy becomes so high that the electron can easily escape from the atom. In single electron atoms, all levels with different within a given  are (to a good approximation) degenerate, and have the same energy. [This approximation is broken to a slight extent by the effect of the magnetic field of the nucleus, and by quantum electrodynamics effects. The latter induce tiny binding energy differences especially for **s** electrons that go nearer the nucleus, since these feel a very slightly different nuclear charge, even in one-electron atoms. See Lamb shift.]

n atoms with multiple electrons, the energy of an electron depends not only on the intrinsic properties of its orbital, but also on its interactions with the other electrons. These interactions depend on the detail of its spatial probability distribution, and so the energy levels of orbitals depend not only on but also on. Higher values of are associated with higher values of energy; for instance, the 2//p// state is higher than the 2//s// state. When = 2, the increase in energy of the orbital becomes so large as to push the energy of orbital above the energy of the //s//-orbital in the next higher shell; when  = 3 the energy is pushed into the shell two steps higher. The filling of the 3d orbitals does not occur until the 4s orbitals have been filled.

The increase in energy for subshells of increasing angular momentum in larger atoms is due to electron-electron interaction effects, and it is specifically related to the ability of low angular momentum electrons to penetrate more effectively toward the nucleus, where they are subject to less screening from the charge of intervening electrons. Thus, in atoms of higher atomic number, the of electrons becomes more and more of a determining factor in their energy, and the principal quantum numbers  of electrons becomes less and less important in their energy placement. The energy sequence of the first 24 subshells (e.g., 1s, 2p, 3d, etc.) is given in the following table. Each cell represents a subshell with and  given by its row and column indices, respectively. The number in the cell is the subshell's position in the sequence. For a linear listing of the subshells in terms of increasing energies in multielectron atoms, see the section below.