[kelvinLTR]

what is the hybridization of the O^- in the NO₃^- ion? I think it is not hybridized as the structure can be explained without the need of the hybridization theory. Or else is it not applicable since resonance occurs?

And a second question. What is the hybridization of O in OH^- ion. I would argue, in the same way that it is unhybridized but one can say it derived from H₂O and since H₂O is SP³ hybridized, so is OH^- ion

[Mr.A]

like , both resonance and hybridization theories explain the existence of any species in reality in a more stable or appropriate way . hybridization , respective to orbitals and resonance respective to resonance structures. O^- in nitrate would have been sp3 hybridized if there was single acceptable Lewis structure for it. but there are three , resonance structures and the pi electron pair in delocalized. for that all the O atoms should have a unhybridized p orbital. So it will bring a higher stability.

OH^- has just one lewis structure.So the way which an obtain a stability is hybridization of orbitals. so the two arguments we an make for O is sp3 hybridized or unhybridized. it will be more stable of having four sp3 hybridized orbitals other than having four p orbitals and one s orbital.  If we consider the hybridization of O in CO₂ in lewis structures and VBT it wont say about any hybridization and it wont be needed. But Hybridization is essential in cases like BeCl₂ and even if add hybridization to the O in CO₂ the three VESPER pairs are SP2 hybridized and orbital wise its more stable.

[opsomath]

Could you explain what you mean by "can be explained without the need of the hybridization theory?"

Hybridization is just a way of describing how orbitals mix to make new orbitals that distribute the electrons in a more stable way. Very few bonding orbitals are pure "s" or "p" orbitals, that kind of thing.

In nitrate, N has three regions of electron density around it, essentially requiring it to be sp2 hybridized.

[kelvinLTR]

I mean like in CCl₄, where hybrid orbitals are not necessary to explain the bonding.

My thinking was a terminal atom does not need hybridization to explain the bonding.

[opsomath]

I think you are confused about the nature of hybridization. Bonding in CCl4 cannot be correctly described without understanding that the bonding orbitals are sp3 on both carbon and chlorine atoms.

The only cases I can think of in which bonding orbitals are nonhybridized is in something like ethyne, in which case there is an sp hybridized "framework" but each carbon has a pair of completely unhybridized p orbitals which make up the pi bonds.

[kelvinLTR]

Why cannot one explain? Chlorine makes only one sigma bong and I cannot find what is wrong in assuming the unhybridized P orbital of Cl makes a sigma bond with SP₃  hybridized Carbon. Am I wrong?

[opsomath]

Cl has three lone pairs around it in addition to the bond.

In order to get a three-dimensional orbital structure with just s and p orbitals, you must have all three sets of p orbitals hybridized to form an sp3 set.

In other words, if you proposed a bonding structure where chlorine had a naked p orbital, we'll call it p_z bonding with an sp3 orbital from carbon, that would limit the other orbitals around chlorine to being no more than sp2 hybridized. In other words, all the other electrons would be stuck in the x-y plane, so you'd have three lone pairs all crammed into the same equatorial plane around chlorine and an empty space up top.

This is obviously not an ideal arrangement thanks to repulsion between electron clouds, so instead the p_z orbital mixes with the others and they all spread out to nearly-equidistant spacing around the chlorine. That's where the well-known approximately 109.5° bond angle comes from.

[kelvinLTR]

I don't think the three lone pairs in s and two p orbitals need to get hybridized at all. Why cannot they be unhybridized, spread across all three dimensions?

And the bond angle of 109⁰.5 can be obtained even without the concept of Hybridization, right?

Going by the argument, one can say F in HF is SP3 hybridized as well. But is it? We don't need hybridization principle to explain the bonding in HF, right?

So what I think is hybridization should be used only when Valence Bond theory fails to explain the bonding.

[opsomath]

Hehe...yes, F in HF is fully SP3 hybridized.