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General Chemistry Principles, Patterns, and Applications, 2011

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Except for hydrogen, Zeff is always less than Z, <strong>and</strong> Zeff increases from left to right as you go across a row.<br />

The energies of the different orbitals for a typical multielectron atom are shown inFigure 6.29 "Orbital Energy Level<br />

Diagram for a Typical Multielectron Atom". Within a given principal shell of a multielectron atom, the orbital energies<br />

increase with increasing l. An ns orbital always lies below the corresponding np orbital, which in turn lies below<br />

the nd orbital. These energy differences are caused by the effects of shielding <strong>and</strong> penetration, the extent to which a<br />

given orbital lies inside other filled orbitals. As shown in Figure 6.30 "Orbital Penetration", for example, an electron<br />

in the 2s orbital penetrates inside a filled 1s orbital more than an electron in a 2p orbital does. Hence in an atom with<br />

a filled 1s orbital, the Zeff experienced by a 2s electron is greater than the Zeff experienced by a 2p electron.<br />

Consequently, the 2s electron is more tightly bound to the nucleus <strong>and</strong> has a lower energy, consistent with the order<br />

of energies shown in Figure 6.29 "Orbital Energy Level Diagram for a Typical Multielectron Atom".<br />

Note the Pattern<br />

Due to electron shielding, Zeff increases more rapidly going across a row of the periodic table than going<br />

down a column.<br />

Figure 6.29 Orbital Energy Level Diagram for a Typical Multielectron Atom<br />

Saylor URL: http://www.saylor.org/books<br />

Saylor.org<br />

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