As important and useful together the octet dominance is in chemical bonding, there are some renowned violations. This walk not mean that the octet dominion is useless—quite the contrary. Just like many rules, there space exceptions, or violations.

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There room three violations come the octet rule. Odd-electron moleculesA molecule v an odd variety of electrons in the valence covering of an atom. Represent the first violation come the octet rule. Back they room few, some stable compounds have an odd number of electrons in your valence shells. With an odd number of electrons, at least one atom in the molecule will have to violate the octet rule. Instances of steady odd-electron molecules room NO, NO2, and also ClO2. The Lewis electron period diagram because that NO is together follows:


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Although the O atom has actually an octet that electrons, the N atom has only seven electrons in that valence shell. Return NO is a stable compound, the is very chemically reactive, as are many other odd-electron compounds.

Electron-deficient moleculesA molecule with less than eight electrons in the valence covering of one atom. Stand for the 2nd violation come the octet rule. These stable compounds have actually less 보다 eight electrons about an atom in the molecule. The most common examples space the covalent link of beryllium and boron. For example, beryllium can type two covalent bonds, resulting in only 4 electrons in the valence shell:


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Boron generally makes just three covalent bonds, resulting in only 6 valence electrons around the B atom. A well-known instance is BF3:


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The third violation to the octet dominance is uncovered in those compounds with more than eight electron assigned to their valence shell. This are called expanded valence covering moleculesA molecule with much more than eight electrons in the valence covering of one atom.. Together compounds are developed only by main atoms in the 3rd row the the routine table or beyond that have empty d orbitals in your valence shells that can participate in covalent bonding. One such link is PF5. The only reasonable Lewis electron dot diagram for this compound has actually the p atom making five covalent bonds:


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Example 9

Identify every violation to the octet dominion by drawing a Lewis electron period diagram.

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ClO SF6

Solution

With one Cl atom and one O atom, this molecule has 6 + 7 = 13 valence electrons, so it is an odd-electron molecule. A Lewis electron dot diagram because that this molecule is together follows:


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In SF6, the main S atom makes six covalent bonds to the six neighboring F atoms, so the is an expanded valence shell molecule. Its Lewis electron dot diagram is together follows:


Test Yourself

Identify the violation to the octet rule in XeF2 by illustration a Lewis electron period diagram.

Answer


Key Takeaway

There room three violations come the octet rule: odd-electron molecules, electron-deficient molecules, and also expanded valence covering molecules.