If the energy of the nitrate ion were the weighted average of the energies of its three resonance forms, just as the structure of the nitrate ion is the weighted average of the structures of its three resonance forms, it should be equal to the energy of one of the three identical resonance forms:.
If the energy of the hybrid were equal to that of a resonance form, given that all chemical entities elementary particles, atoms, molecules, etc. Since the nitrate ion exists as the hybrid, not as a resonance form, it can be inferred that the energy of the hybrid is lower than that of any of the resonance forms. According to resonance theory then, the energy of a molecule is lower than that of the lowest-energy resonance form. Since the nitrate ion has lower energy and, therefore, is more stable than any of its resonance forms, the nitrate ion is said to be resonance stabilized.
There are two misconceptions about resonance theory among beginning students, likely due to literal interpretation of the word resonance. They are described below, using the nitrate ion as the example. Misconception 1: The nitrate ion exists as resonance form 1 for a moment and then changes either to resonance form 2 or to resonance form 3 , which interconvert, or revert to 1. The structure of the nitrate ion is not 1 nor 2 nor 3 but the hybrid and does not change with time unless undergoing a reaction.
Misconception 2: In a sample of nitrate ions, at a given moment, one-third of the ions exist as resonance form 1 , another one-third as resonance form 2 , and the remaining one-third as resonance form 3. In a sample of nitrate ions, at a given moment, all ions have the same structure, which is the hybrid. The classic analogy used to clarify these two misconceptions is the mule Morrison, R. Organic Chemistry , fifth edition; Allyn and Bacon: Boston, , pg. Biologically, a mule is a hybrid of a horse and a donkey.
This does not mean that a mule resembles a horse for a moment and then changes to resemble a donkey. The appearance of a mule is a combination of that of a horse and that of a donkey and does not change with time. Nor does it mean that, in a herd, some mules resemble a horse and the others a donkey. In a herd, all mules have the same appearance, which is a combination of a horse and a donkey. The weakness of this analogy is that horses and donkeys do exist, whereas resonance forms are strictly hypothetical.
A better analogy, cited in Morrison and Boyd, is the rhinoceros. Upon seeing a rhinoceros, one could describe it as the hybrid of a dragon and a unicorn, two creatures that do not exist.
Resonance forms are Lewis diagrams, which are based on valence bond theory. They must, therefore, obey the basic rules of valence bond theory. Thus, hydrogen can not have more than two valence electrons; Period-two elements can not have more than eight valence electrons; elements in Period three and below may have more than eight valence electrons. In none of the resonance forms of the nitrate ion are there more than eight valence electrons on any of the atoms.
All resonance forms must have the same sigma-bond framework, differing only in the locations of pi electrons and nonbonded valence electrons. They differ from one another only in the locations of pi electrons and lone pairs. Organic chemists increasingly violate this rule in order to explain the structures of reactive intermediates as resonance-stabilized species.
The three forms of the nitrate ion are identical and, therefore, have the same stability. Consequently, they contribute equally to the hybrid. Connect and share knowledge within a single location that is structured and easy to search. I made some simple drawings to try to explain what I don't understand:. Does the "electron from outside" that the oxygen receives, as indicated in the drawing, comes from the nitrogen atom? Is this the correct line of thinking?
Coordination structures are varied,. If you are thinking about it like literally adding O to the nitrite ion then yes, the two electrons the oxygen receives are from nitrogen. Imagine moving the nitrogen lone pair to the oxygen to give it a full octet and forming a single bond in the process.
You will notice that the Lewis structures will match the "organiker" structures of Uncle Al. N has 1 lp means 2 unused electrons. N will share its lone pair with Oxygen oxygen will not use its 6 e, only 2 e of N will be shared by both O and N , this type of bonding is known as coordinate bond.
If any confusion left, you can check some videos of coordinate bonding , then you will surely understand. Sign up to join this community. The best answers are voted up and rise to the top. Stack Overflow for Teams — Collaborate and share knowledge with a private group.
Create a free Team What is Teams? Start to mark those nine valence electrons pairs on outside atoms oxygen atoms as lone pairs. One oxygen atom will take three lone pairs following the octal rule oxygen and nitrogen atoms cannot keep more than eight electrons in their valence shells. All nine valence electrons pairs 9 are spent when lone pairs are marked on oxygen atoms. Check charges on atoms and mark them as below.
Charges are important to decide the lewis structure of the ion. The drawn structure for NO 3 - is not a stable structure because oxygen atoms and nitrogen atoms have charges. When a molecule or ion has so many charges on atoms, that structure is not stable. Now, we should try to minimize charges by converting lone pair or pairs which exist on oxygen atoms to bonds. So we convert one lone pair of one oxygen atom as a N-O bond.
Now there is a double bond between nitrogen and one oxygen atom. There are also two single bonds N-O with nitrogen atom and other oxygen atoms. In new structure, charges of atoms are reduced. Now there is no any charge on one oxygen atom. Now you understand this structure of NO 3 - is more stable than previous structure due to less charges on atoms. But, We cannot convert more lone pairs of other oxygen atom to make a bond with nitrogen atom because nitrogen cannot keep more than eight electrons in its last valence shell.
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