Name: resonance in nitrite and carbonate ions
Uploaded: 2025-05-22T09:05:33.000Z
Duration: 2 min 16 s
Channel: JoVE

Most molecules and ions are represented by a single Lewis structure. However, in particular compounds, some electrons are delocalized over multiple bonds or atoms rather than localized to a specific bond or atom. These compounds can be represented accurately with multiple Lewis structures.
Consider the Lewis structure for sulfur trioxide. The single bonds between each oxygen and the central sulfur atoms satisfy the octet for the oxygen atoms. However, to reach a full octet for the sulfur, an additional bond must be formed between sulfur and one of the oxygen atoms.
These multiple Lewis structures of sulfur trioxide are called resonance structures or contributing structures. The spatial positions of all of the component atoms remain the same; however, the valence electrons are distributed differently.
These double-headed arrows can be thought of as commas and should not be confused with resonance structures being in equilibrium. In these molecules, the actual structure is the weighted average or a hybrid of its resonance structures.
Resonance structures are identified by &#8216;electron pushing&#8217;, or transforming lone pairs into bonds and vice versa, as denoted with curved arrows. This maps the delocalized areas.
Such delocalization results in resonance stabilization&#8212;that is, a molecule with a lower potential energy than that of any theoretical non-delocalized structure.
If a contributing structure is lower in energy than another, it more closely resembles the actual molecular structure. Certain preferences are used to estimate the relative energies of various contributing structures.
Firstly, structures in which all atoms have filled valence shells are more stable. Secondly, structures with a greater number of covalent bonds are more stable. Thirdly, structures that minimize formal charges are more stable.
Finally, structures carrying negative charges on more electronegative atoms and positive charges on less electronegative atoms are more stable.

resonantie en hybride structuren

Resonance and Hybrid Structures

Volgens de resonantietheorie is, als twee of meer Lewis-structuren met dezelfde rangschikking van atomen kunnen worden geschreven voor een molecuul, ion of radicaal, de feitelijke verdeling van elektronen een gemiddelde van die weergegeven door de verschillende Lewis-structuren.


 Resonantiestructuren en resonantiehybriden


 De Lewis-structuur van een nitriet-ion (NO_2−) kan feitelijk op twee verschillende manieren worden getekend, te onderscheiden door de locaties van de N−O- en N=O-bindingen.


 <img alt="Figure1" src="/files/ftp_upload/11684/11684 PT Figure 1.svg" style="text-align: center; height: 50px;" />


 Als nitrietionen een enkele en een dubbele binding bevatten, wordt verwacht dat de twee bindingslengtes verschillend zijn. Een dubbele binding tussen twee atomen is korter (en sterker) dan een enkele binding tussen dezelfde twee atomen. Experimenten tonen echter aan dat beide N−O-bindingen in NO_2− dezelfde sterkte en lengte hebben, en identiek zijn in alle andere eigenschappen. Het is niet mogelijk om één enkele Lewis-structuur voor NO_2− te schrijven waarin stikstof een octet heeft en beide bindingen gelijkwaardig zijn.


 In plaats daarvan wordt het concept van resonantie gebruikt: de feitelijke verdeling van elektronen in elk van de stikstof-zuurstof bindingen in NO_2- is het gemiddelde van een dubbele binding en een enkele binding.


 De individuele Lewis-structuren worden resonantiestructuren genoemd. De feitelijke elektronische structuur van het molecuul (het gemiddelde van de resonantie vormen) wordt een resonantiehybride van de individuele resonantievormen genoemd. Een tweepuntige pijl tussen Lewis-structuren geeft aan dat het resonantievormen zijn.


 <img alt="Figure2" src="/files/ftp_upload/11684/11684 PT Figure 2.svg" style="text-align: center; height: 50px;" />


 Het carbonaation CO_3^2− is een tweede voorbeeld van resonantie.


 <img alt="Figure3" src="/files/ftp_upload/11684/11684 PT Figure 3.svg" style="text-align: center; height: 75px;" />

<ul style="padding-left: 35px; list-style-type: disc;">
 <li>Één zuurstofatoom moet een dubbele binding met koolstof hebben om het octet op het centrale atoom te voltooien.</li>
 <li>Alle zuurstofatomen zijn echter gelijkwaardig, en de dubbele binding kan uit elk van de drie atomen ontstaan. Dit geeft aanleiding tot drie resonantievormen van het carbonaation.</li>
 <li>Aangezien drie identieke resonantiestructuren kunnen worden geschreven, is het bekend dat de feitelijke rangschikking van elektronen in het carbonaation het gemiddelde is van de drie structuren.</li>
 <li>Experimenten laten opnieuw zien dat alle drie de C–O-obligaties precies hetzelfde zijn.</li>
</ul>

 Een molecuul dat wordt beschreven als een resonantiehybride bezit nooit een elektronische structuur die door één van beide resonantievormen wordt beschreven. Het fluctueert niet tussen resonantievormen; maar de feitelijke elektronische structuur is altijd het gemiddelde van dat wat door alle resonantievormen wordt getoond.


 Deze tekst is aangepast van <a href="https://openstax.org/books/chemistry-2e/pages/7-4-formal-charges-and-resonance">Openstax, Chemistry 2e, Chapter 7.4 Formal Charges and Resonance</a>.

Resonantie en hybride structuren

According to the theory of resonance, if two or more Lewis structures with the same arrangement of atoms can be written for a molecule, ion, or radical, ...

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resonance in nitrite and carbonate ions

Resonance explains why some Lewis structures do not match the measured properties of a molecule or ion. When two or more Lewis structures have the same atom arrangement, the real electron distribution is an average of the structures shown.

The nitrite anion, NO2−, is one example. It can be drawn in two ways, with the N–O and N=O bonds in different places. If nitrite had one single bond and one double bond, the two bond lengths should be different, because a double bond is shorter and stronger than a single bond.

Experiments show that both N–O bonds in NO2− have the same length and strength. They are identical in all other properties as well. A single Lewis structure cannot show this and still give nitrogen an octet, so resonance is used to describe the ion.

The separate Lewis structures are called resonance structures. The true electronic structure is called a resonance hybrid, which is the average of the resonance forms. A double-headed arrow between Lewis structures shows that they are resonance forms. Nitrite does not switch back and forth between them. Its electron distribution is always the average of the forms.

The carbonate anion, CO3 2−, gives a second example. One oxygen must form a double bond to carbon to complete the octet on the central atom, but each oxygen atom is equivalent. That means the double bond can be placed with any one of the three oxygens, creating three resonance forms.

Because the three resonance structures are identical, the electron arrangement in carbonate is the average of all three. Experiments show that all three C–O bonds are exactly the same. A resonance hybrid never has the exact electronic structure of just one resonance form.

Resonance in Nitrite and Carbonate Ions

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Explore how resonance explains equal bond lengths in nitrite and carbonate ions, and learn the difference between resonance structures and a resonance hybrid.

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Resonance in Nitrite and Carbonate Ions

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