40
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What is resonance, and are resonance structures real?
This answer is intended to clear up some misconceptions about resonance which have come up many times on this site.
Resonance is a part of valence bond theory which is used to describe delocalised ...
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18
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What is charge shift bonding?
Geoff has summarized well the mathematical, VB wavefunction-based description of charge-shift bonding. This answer aims to provide further exposition, from the perspective of the distribution of the ...
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18
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Do Li4 or Li8 molecules exist?
Yes, they do exist and were characterised spectroscopically, see here (and there is a note on similar clusters for sodium):
Blanc, J.; Bonačić‐Koutecký, V.; Broyer, M.; Chevaleyre, J.; Dugourd, P.; ...
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What is resonance, and are resonance structures real?
Bon has a very nice example of motion potentially restricted because of a barrier, and although it turns out that this is not the case for the norbornyl cation, there are simpler examples that do show ...
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Can an atom have more than 8 valence electrons? If not, why is 8 the limit?
Why 8? has not really been addressed by the above answers, and while tangential to the question, it is somewhat important to be considered. In general, but not always, atoms react to form complete ...
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15
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How can the hybridisation schemes of transition metal complexes be determined?
Firstly, note that hybridisation theory as applied to transition metal complexes is an incorrect, flawed theory. It is an attempt to rationalise experimental observation (e.g. geometries), but in the ...
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11
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How are the hybrid orbitals of sulfur hexafluoride shaped?
If you limit consideration to hybridization of atomic orbitals, a good reference to see is On the role of d orbitals in sulfur hexafluoride J. Am. Chem. Soc., 1986, 108 (13), pp 3586–3593.
First, it ...
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11
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What is actually the difference between valence bond theory and molecular orbital theory?
Comparing modern valence bond and electronic structure theories one can argue that the generalized valence bond (GVB) wave function can be regarded as a special form of the multi-configurational self-...
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Has it been observed that the dihydrogen molecule dissociates into ions?
Surely1. At the end of the day, it is just the matter of supplying enough energy: the homolysis requires approximately 4.5 eV per hydrogen molecule, while for heterolysis more than 17 eV per molecule ...
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10
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Hybrid orbitals forming molecular orbitals
It is still LCAO-MO theory, but just dumbed down a lot. The difference is that, instead of feeding the "pure" atomic orbitals into the LCAO mechanism, you carry out an additional mathematical step in ...
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10
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How are the hybrid orbitals of sulfur hexafluoride shaped?
Hybridisation is determined by geometry!
This is the number one thing that you should learn from this answer. If you know the geometry of a molecule then you can work out the hybridisation of the ...
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9
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Comparing bond angles in carbonyl dichloride and carbonyl dibromide
The reasoning you utilized for comparing the bond angles of $\ce{NH3}$, $\ce{NF3}$, and $\ce{NCl3}$, while sensible, is simplistic and works best only for a few cases where weighing the factors of ...
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8
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Delocalised electron in graphite
It's just a matter of definition. If a "layer" is understood as an infinitely thin plane passing through the centers of carbon atoms, then the electron density of the huge delocalized $\pi$ orbital is ...
- 31k
8
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Valence Bond theory, VSEPR theory and predicting the shapes of the molecules
VSEPR theory is a purely observational model, based on empirical knowledge. Many of the "rules" were added to fit the theory to what has been observed. It has quite a lot limitations and may ...
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8
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Where do the lone pairs go in the "true" resonance structure?
Resonance is a concept resulting from valence bond (VB) theory. Within this theory it is impossible to describe delocalisation. However, every configuration within this framework can be expressed as a ...
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Bonding in Zeise's salt
The bond between $\ce {Pt} $ and ethene is not purely a $\sigma $ bond and also not a pure $\pi $ bond. The bonding actually consists of a combination of both bonding and back-bonding effect.
If ...
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8
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Valence bond theory and molecular orbital theory — how do they complement one another?
You are correct that Valence Bond Theory (VB) is still very active in the chemical bonding community along with MOs. I recommend this article/conversation by Roald Hoffmann about this topic (Acc. Chem....
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Is dihydrogen the only example of overlap between two s orbitals?
You don't need particularly exotic things to get a counterexample. Metal–metal bonding in mercury(I) compounds is quite prevalent, where the electronic configuration is $\ce{Hg+}$: $\ce{[Xe](4f^14)(5d^...
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How does the MO-LCAO theory explain the direction of valence bonds?
The relevant MO analysis for understanding the effect of bond angle on energy is a "Walsh diagram," which for compounds of the type $\ce{AH2}$ looks like this:
Source is this post on ChemSE ...
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7
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If I can't draw resonance structures for a pi system, does that mean it doesn't exist?
If there are adjacent, parallel, overlapping p-orbitals in a molecule, the electrons will be delocalized over all such atoms. While the negative charge isn't delocalized over every atom in the ...
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7
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Explain on the basis of valence bond theory that tetracyanonickelate(II) ion with square planar structure is diamagnetic
@M.L has already provided the solution as per VBT, but that answer seems to have some flaws when it comes to CFT (looks like he has corrected the mistakes now). So, I would like to take some time to ...
- 3,075
6
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CO₂ molecule π bonds
Recall the definition of σ-bonds. They are caused by the head-on overlapping of the orbitals.
$s$ orbitals always, and only form σ-bonds while the $p$ orbitals in the direction of bond axis (which ...
6
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Buckminsterfullerene double bonds
All carbon atoms in fullerene are part of one "double bond", as you draw it. In quantum chemical reality, the structure of the fullerene is made up by fixed "single" bonds between those 60 sp2 ...
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Ionization energy of C2-, C2, and C2+
Bond order has to do nothing with ionization energy, it is the bond dissociation energy which has to be dealt with bond order. For minimum ionization energy, the electron has to be lost from the ...
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Which combinations of orbitals lead to pi bonds according to Valence Bond Theory?
Here are the requirements for a $\pi$ bond:
Each contributing orbital has to have exactly one nodal plane containing the bond axis. There can be other nodal planes that might cut through the axis, ...
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Why would a metal form an ionic compound with a nonmetal from a lower period?
Generally, forming 2 isolated ions from 2 isolated atoms is not thermodynamically favoured, as ionization energies are higher than electron affinities.
But, ion formation is thermodynamically favoured,...
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5
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Difference between valency and oxidation state
Valency is a term used to describe the number of bonds a given atom undergoes in a certain environment. For example, the carbon atom in all of the following substances is tetravalent:
methane
...
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5
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Similarities and Differences between Resonance and MCSCF treatments
Great question - it engages with the difficult task concerning conceptualization of molecules, and how our models and jargon we use can often cause confusion while also helping to explain significant ...
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What is charge shift bonding?
I think the two answers currently here are excellent, very detailed and a great read. I thought I would give a different perspective on charge-shift bonding, from the view of the virial theorem.
The ...
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