Electrostatic Effects and Energy-Level Splitting

Much greater shielding is provided by inner electrons. Because they spend nearly all their time between the outer electrons and the nucleus, inner electrons shield outer electrons very effectively, in fact, much more effectively than do electrons in the same sublevel. Shielding by inner electrons greatly lowers the felt by outer electrons. 

Identifying electrons in many-electron atoms requires four quantum numbers three (n, /, rrii) describe the orbital, and a fourth (/Dj) describes electron spin. The exclusion principle requires each electron to have a unique set of four quantum numbers therefore, an orbital can hold no more than t wo electrons, and their spins must be paired (opposite). Electrostatic interactions determine orbital energies as follovws  

Greater nuclear charge low/ers orbital energy and makes electrons harder to remove. 

Electron-electron repulsions raise orbital energy and make electrons easier to remove. Repulsions have the effect of shielding electrons from the full nuclear charge, reducing it to an effective nuclear charge, Zgff. Inner electrons shield outer electrons most effectively. 

Greater radial probability distribution near the nucleus (greater penetration) makes an electron harder to remove because it is attracted more strongly and shielded less effectively. As a result, an energy level (shell) is split into sublevels (subshells) with the energy order s p d f. 

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The Electron-Spin Quantum Number The Exclusion Principle Electrostatic Effects and Energy-Level Splitting... 

Figure 11.12 illustrates the effect of i-tixis stretching on the and orbitals in an octahedral complex. Orbitals having a component (the dj, d,j, and t/ ) will experience a decrease in electrostatic repulsions fbom the ligands and will therefore be stabilized. At the same time, the non-i orbitals will be raised in energy, with the barycenter remaining constant. The overall result is that the level is split into two levels, an upper bi and a lower (J z) and the set is split into u (d y)... 

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