The ground state of lithium (Z=3) has two electrons in the 1s level, and one in the 2s. Consider an excited state, in which the outermost electron has been raised to the 3p level. (a) Estimate the energy of this excited electron, assuming that it is completely outside the orbitals of the inner two electrons. (Hint: assume that the inner two electrons "screen" part of the nuclear charge, so that you can treat the remaining electron as simply being in a state of a hydrogen atom.) (b) The observed value for the energy of a 3p electron in an excited state of lithium is 1.556eV, which differs from the value you (hopefully) found in (a) by a few percent. The observed energy of the 3d level of the lithium atom is 1.513eV. Briefly explain why the observed energy of the 3d state is in better agreement with the energy estimated in part (a) than is the observed energy of the 3p state