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General Chemistry Principles, Patterns, and Applications, 2011

General Chemistry Principles, Patterns, and Applications, 2011

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Unlike earlier diagrams, only the molecular orbital energy levels for the molecules are shown here. For simplicity,<br />

the atomic orbital energy levels for the component atomshave been omitted. For Li2 through N2, the s 2pz<br />

orbital is higher in energy than the p2px,y orbitals. In contrast, the s 2pz orbital is lower in energy than<br />

the p2px,y orbitals for O2 <strong>and</strong> F2 due to the increase in the energy difference between the 2s <strong>and</strong> 2p atomic<br />

orbitals as the nuclear charge increases across the row.<br />

Completing the diagram for N2 in the same manner as demonstrated previously, we find that the 10 valence electrons<br />

result in 8 bonding electrons <strong>and</strong> 2 antibonding electrons, for a predicted bond order of 3, a triple bond. Experimental<br />

data show that the N–N bond is significantly shorter than the F–F bond (109.8 pm in N2 versus 141.2 pm in F2), <strong>and</strong><br />

the bond energy is much greater for N2 than for F2 (945.3 kJ/mol versus 158.8 kJ/mol, respectively). Thus the<br />

N2 bond is much shorter <strong>and</strong> stronger than the F2 bond, consistent with what we would expect when comparing a<br />

triple bond with a single bond.<br />

E X A M P L E 1 0<br />

Use a qualitative molecular orbital energy-level diagram to predict the electron configuration, the bond<br />

order, <strong>and</strong> the number of unpaired electrons in S 2, a bright blue gas at high temperatures.<br />

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

Saylor.org<br />

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