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

La mayoría de las moléculas e iones están representados por una sola estructura de Lewis. Sin embargo, en compuestos particulares, algunos electrones se deslocalizan a través de múltiples enlaces o átomos en lugar de localizarse en un enlace o átomo específico. Estos compuestos se pueden representar con precisión con múltiples estructuras de Lewis.
Considere la estructura de Lewis para el trióxido de azufre. Los enlaces simples entre cada oxígeno y los átomos centrales de azufre satisfacen el octeto de los átomos de oxígeno. Sin embargo, para alcanzar un octeto completo para el azufre, se debe formar un enlace adicional entre el azufre y uno de los átomos de oxígeno.
Estas múltiples estructuras de Lewis de trióxido de azufre se denominan estructuras de resonancia o estructuras contribuyentes. Las posiciones espaciales de todos los átomos componentes siguen siendo las mismas; Sin embargo, los electrones de valencia se distribuyen de manera diferente.
Estas flechas de doble punta se pueden considerar como comas y no deben confundirse con las estructuras de resonancia que están en equilibrio. En estas moléculas, la estructura real es el promedio ponderado o un híbrido de sus estructuras de resonancia.
Las estructuras de resonancia se identifican por "empuje de electrones", o transformación de pares solitarios en enlaces y viceversa, como se denota con flechas curvas. Esto mapea las áreas deslocalizadas.
Tal deslocalización da como resultado la estabilización de la resonancia, es decir, una molécula con una energía potencial más baja que la de cualquier estructura teórica no deslocalizada.
Si una estructura contribuyente es más baja en energía que otra, se asemeja más a la estructura molecular real. Ciertas preferencias se utilizan para estimar las energías relativas de varias estructuras contribuyentes.
En primer lugar, las estructuras en las que todos los átomos tienen capas de valencia rellenas son más estables. En segundo lugar, las estructuras con un mayor número de enlaces covalentes son más estables. En tercer lugar, las estructuras que minimizan los cargos formales son más estables.
Por último, las estructuras que llevan cargas negativas en átomos más electronegativos y cargas positivas en átomos menos electronegativos son más estables.

resonancia y estructuras híbridas

Resonance and Hybrid Structures

Según la teoría de la resonancia, si se pueden escribir dos o más estructuras de Lewis con la misma disposición de átomos para una molécula, ion o radical, la distribución real de electrones es un promedio de la que muestran las diversas estructuras de Lewis.


 Estructuras de resonancia e híbridos de resonancia


 La estructura de Lewis de un anión nitrito (NO2-) en realidad se puede dibujar de dos maneras diferentes, que se distinguen por las ubicaciones de los enlaces N–O y N=O.


 <img alt="Figure1" src="/files/ftp_upload/11684/11684%20PT%20Figure%201.svg" style="text-align: center; height: 50px;">


 Si los iones nitrito contienen un enlace simple y uno doble, se espera que las longitudes de los dos enlaces sean diferentes. Un doble enlace entre dos átomos es más corto (y más fuerte) que un enlace simple entre los mismos dos átomos. Sin embargo, los experimentos muestran que ambos enlaces N–O en el NO2- tienen la misma fuerza y ​​longitud, y son idénticos en todas las demás propiedades. No es posible escribir una única estructura de Lewis para el NO2- en la que el nitrógeno tenga un octeto y ambos enlaces sean equivalentes.


 En cambio, se utiliza el concepto de resonancia: la distribución real de electrones en cada uno de los enlaces nitrógeno-oxígeno en el NO2- es el promedio de un enlace doble y un enlace simple.


 Las estructuras de Lewis individuales se denominan estructuras de resonancia. La estructura electrónica real de la molécula (el promedio de las formas de resonancia) se denomina híbrido de resonancia de las formas de resonancia individuales. Una flecha de dos puntas entre las estructuras de Lewis indica que son formas de resonancia.


 <img alt="Figure2" src="/files/ftp_upload/11684/11684%20PT%20Figure%202.svg" style="text-align: center; height: 50px;">


 El anión carbonato, CO32-, proporciona un segundo ejemplo de resonancia.


 <img alt="Figure3" src="/files/ftp_upload/11684/11684%20PT%20Figure%203.svg" style="text-align: center; height: 75px;">


 <ul>
 <li>Un átomo de oxígeno debe tener un doble enlace con el carbono para completar el octeto del átomo central.</li>
 <li>Sin embargo, todos los átomos de oxígeno son equivalentes y el doble enlace podría formarse a partir de cualquiera de los tres átomos. Esto da lugar a tres formas de resonancia del ion carbonato.</li>
 <li>Dado que se pueden escribir tres estructuras de resonancia idénticas, se sabe que la disposición real de los electrones en el ion carbonato es el promedio de las tres estructuras.</li>
 <li>Nuevamente, los experimentos muestran que los tres enlaces C–O son exactamente iguales.</li>
 </ul>
 

 Una molécula descrita como híbrido de resonancia nunca posee una estructura electrónica descrita por ninguna de las formas de resonancia. No fluctúa entre formas de resonancia; más bien, la estructura electrónica real es siempre el promedio de la mostrada por todas las formas de resonancia.

Resonancia y estructuras híbridas

De acuerdo con la teoría de la resonancia, si dos o más estructuras de Lewis con la misma disposición de átomos se pueden escribir para una molécula, ion o 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.

Resonance in Nitrite and Carbonate Ions | JoVE K12

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Resonance in Nitrite and Carbonate Ions

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