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Molecular Orbitals of Nitric Oxide

Nitric oxide (NO) is a heteronuclear diatomic molecule formed from nitrogen and oxygen that plays important roles in both air pollution and biological processes. Its bonding cannot be explained by Lewis structures or valence bond theory due to its odd number of electrons. Molecular orbital theory provides an energy diagram showing that one electron occupies a degenerate orbital, giving NO a bond order of 2 1/2 and properties between nitrogen and oxygen gas molecules. This description matches experimental bond measurements, demonstrating molecular orbital theory can explain molecules like NO that have an odd number of electrons.

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711 views1 page

Molecular Orbitals of Nitric Oxide

Nitric oxide (NO) is a heteronuclear diatomic molecule formed from nitrogen and oxygen that plays important roles in both air pollution and biological processes. Its bonding cannot be explained by Lewis structures or valence bond theory due to its odd number of electrons. Molecular orbital theory provides an energy diagram showing that one electron occupies a degenerate orbital, giving NO a bond order of 2 1/2 and properties between nitrogen and oxygen gas molecules. This description matches experimental bond measurements, demonstrating molecular orbital theory can explain molecules like NO that have an odd number of electrons.

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hakim
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NO Molecular Orbital Theory : Energy Diagram

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electronegative electronegative

Nitric oxide (NO) is an example of a heteronuclear diatomic molecule. The reaction of O2 with N2 at high
temperatures in internal combustion engines forms nitric oxide, which undergoes a complex reaction with
O2 to produce NO2, which in turn is responsible for the brown color we associate with air pollution.
Recently, however, nitric oxide has also been recognized to be a vital biological messenger involved in
regulating blood pressure and long-term memory in mammals.

Because NO has an odd number of valence electrons (5 from nitrogen and 6 from oxygen, for a total of 11),
its bonding and properties cannot be successfully explained by either the Lewis electron-pair approach or
valence bond theory. The molecular orbital energy-level diagram for NO (Figure 11.5.1311.5.13) shows
that the general pattern is similar to that for the O2molecule (see Figure 11.5.1111.5.11). Because 10
electrons are sufficient to fill all the bonding molecular orbitals derived from 2p atomic orbitals, the 11th
electron must occupy one of the degenerate π* orbitals. The predicted bond order for NO is therefore (8-3)
÷ 2 = 2 1/2 . Experimental data, showing an N–O bond length of 115 pm and N–O bond energy of 631
kJ/mol, are consistent with this description. These values lie between those of the N2 and O2 molecules,
which have triple and double bonds, respectively. As we stated earlier, molecular orbital theory can
therefore explain the bonding in molecules with an odd number of electrons, such as NO, whereas Lewis
electron structures cannot.

Molecular Orbital Energy-Level Diagram for NO. Because NO has 11 valence electrons, it is

paramagnetic, with a single electron occupying the pair of orbitals.

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