guy
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Nitrate Structure
The nitrate structure I see in books is
O
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N--O
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O
The charges are +1 for the N and -1 for both of the O. According to the electroneutrility principle shouldn't the structure be
O
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N=O
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O
with everything execpt one O atom being (-1), which makes more sense because thats were the cation would be attached.
[Edited on 12/10/2005 by guy]
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The_Davster
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Its a resonance thing, it can be thought of as if the double bond between the nitrogen and oxygen is constantly switching between all the oxygens,
leaving only one oxygen with a double bond at any given time. However, the real nitrate ion has N-O bonds that have 1/3 the properties of a double
bond, and 2/3 the properties of a single bond. The oxygens can be thought of having 1/3 of a negative charge each.
Your second structure does not happen as you just killed nitrogen's octet, which it cannot exceed.
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Nerro
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I believe one of the reasons why HNO3 is a strong acid is because the anion in it is so thoroughly stabilized.
The reason for this is that there are basically three predominantly possible resonance structures in which the NO3- ion can exist. This means that in
practice the electron is spread quite nicely over the entire ion rather than being confined to one atom which reduces the stress on the molecule
considerably (thus stabilizing it).
This picture shows you the three resonant extremes between which the molecule can resonate:
As stated by rogue chemist nitrogen can not make 5 bonds. It has four pairs when it's made single bonds with all the O's around it (1 lone
pair and three shared pairs). And it can form an iditional bond (pi bond) by forming a dative bond with its own lone pair. This causes the N to "lose"
1 electron hence it's single positive charge.
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unionised
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Just to clarify things, the bond angles are all equal too; 120 degrees, rather than right angles as drawn- (I'm sure this is just due to the
difficulty of getting decent grahics).
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Nerro
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@unionised
Yep, it is.
You can calculate the bond angles quite easily in this case. There are three sigma bonds and one pi bond. That means the N is
sp<sup>2</sup> hybridized. Which means 1 s-orbital and 2 p orbitals have hybridized (melted together one might say) to form three
sp<sup>2</sup> orbitals which all have equal energy and shape. According to VSEPR (Valence Shell Electron Pair Repulsion theory) they must
form a trigonal plane. The pi bond can (in this case) be seen as two blobs (one above, one below) that cover the entire (triangular) molecule.
Just for clarity's sake; Orbitals are regions in which an electron might be found.
[Edited on Sun/Dec/2005 by Nerro]
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