its interactions with the other electrons in other orbitals. This requires consideration of the l quantum number. Higher values of l are associated with higher values of energy; for instance, the 2p state is higher than the 2s state. When l = 2, the increase in energy of the orbital becomes large enough to push the energy of orbital above the energy of the s-orbital in the next higher shell; when l = 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.

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