Subshells ground-state configuration

The ground-state configurations and corresponding values of L, S, and J for the ions with valence d and/subshells are given in Table 8.2. 

Using these quantum mechanical rules, we can now explore the underlying basis of the Periodic Table. To define the ground state configuration of an atom, we add electrons beginning with the lowest energy subshell until the correct number of electrons (equal to the elements atomic number) have been added. This procedure is called the aufbau ( building-up ) principle. 

Now consider two electrons in the same subshell equivalent electrons). Equivalent electrons have the same value of n and the same value of /, and the situation is complicated by the necessity to avoid giving two electrons the same four quantum numbers. Hence not all the terms derived for nonequiveilent electrons are possible. As an example, consider the terms arising from two equivalent p electrons, an np configuration. (The carbon ground-state configuration is s 2 2p. ) The possible values of m and for the two electrons are hsted in Table 11.1, which also gives md A/5. 

We begin with the ground state of He2. The separated helium atoms each have the ground-state configuration Is. This closed-subshell configuration does not have any unpaired electrons to form valence bonds, and the VB wave function is simply the antisymmetrized product of the atomic-orbital functions ... 

Diatomic hydrides are a special case, since H has only a Is valence AO. Consider HF as an example. The ground-state configurations of the atoms are Is for H and ls 2s 2p for F. We expect the filled Is and 2s F subshells to take little part in the bond-... 

It is important to understand what gives rise to the established coexisting intruder band in doubly closed subshell 9(>Zr. The slight predominance of the intruder deformed configuration in the ground state wavefunction of lO Mo shown in Fig. 1(b) cannot explain the tremendous difference between the alpha-pickup strengths to the two 0+ states of 9 >Zr clearly demonstrated by Fig. 1(a). This is not unexpected, since the simultaneous occurrence of proton and neutron subshell closures should produce a marked difference with respect to other nuclei near the middle of the 50 to 82 neutron shell where two-proton, two-hole excitations can account entirely for the observed shape coexistence phenomena. 

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