Questions tagged [valence-bond-theory]

Questions about how the atomic orbitals of the dissociated atoms combine to give individual chemical bonds when a molecule is formed.

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64
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1answer
9k views

Why does F replace the axial bond in PCl5?

Why does $\ce{F}$ replace an axial bond in $\ce{PCl5}$? I realize that it would be more stable there than at equatorial bond, but what is the reason of its stability? Similarly in $\ce{AB4}$ type of ...
45
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4answers
7k views

What is resonance, and are resonance structures real?

My teacher told me about resonance and explained it as different structures which are flipping back and forth and that we only observe a sort of average structure. How does this work? Why do the ...
89
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2answers
35k views

What is Bent's rule?

I'm all bent out of shape trying to figure out what Bent's rule means. I have several formulations of it, and the most common formulation is also the hardest to understand. Atomic s character ...
176
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8answers
156k views

Can an atom have more than 8 valence electrons? If not, why is 8 the limit?

According to some chemistry textbooks, the maximum number of valence electrons for an atom is 8, but the reason for this is not explained. So, can an atom have more than 8 valence electrons? If ...
13
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1answer
9k views

Delocalization of π-electrons in nitrate ion

Benzene and nitrate ion are given in my textbook as examples for the delocalization of π-electrons. Benzene, due to symmetry of its resonating structures, is simple enough. We assume that σ-electrons ...
35
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3answers
21k views

What is actually the difference between valence bond theory and molecular orbital theory?

Recently I have read about both of the concepts in my book (Physical Chemistry by Atkins, Paula). It was literally a reading; though I could understand the language and superposition of orbitals, ...
23
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3answers
2k views

What is charge shift bonding?

Can someone explain to me charge shift bonding? I recognize that it is proposed as another domain of bonding - one different from ionic and covalent bonding. I am also told that $\ce{C-F}$ exhibits ...
7
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3answers
8k views

Does the shared electron in Covalent bonds revolve around nucleus?

We know that electrons are charges that revolve around the nucleus. Then, when in covalent bonds the electron is shared; does the electron obey the rule?
7
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2answers
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How are the hybrid orbitals of sulfur hexafluoride shaped?

On the fluorine end the fluoride atoms are simply completing a $3p$ orbital. On the sulfur end one could posit a hybrid of one $3s$ orbital, two $3p$ orbitals and a three inner $2p$ orbitals. However,...
8
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1answer
36k views

Why an asymmetric geometry with sp3d and sp3d3 hybridization?

A molecule in which the central atom is $sp^3d^2$ hybridized ($\ce{SF_6}$), for example, acquires an octahedral shape, which can be explained by assuming that the hybrid orbitals arrange themselves to ...
19
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2answers
3k views

What does it mean when it is said that an sp³ orbital has 25% s character?

My textbook frequently mentions: $\mathrm{sp^3}$ hybrid orbital has 25% $\mathrm{s}$-character and 75% $\mathrm{p}$-character. What are these "characters"? And how do these characters influence ...
9
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2answers
2k views

Why is the resonance concept not required in molecular orbital theory?

In valence bond theory, resonance plays a pivoting role; why isn't such concept needed in MO theory? Why is it told that "MO theory provides a global, delocalized perspective on chemical bonding"? (...
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1answer
2k views

Determine the bond angle in a compound [closed]

How can we find the bond angle between 3 atoms in a compound? Please specify an equation which can be used for all compounds.
7
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1answer
2k views

What is the highest possible expanded octet?

Often called "hypervalent", chemicals like phosphorous pentachloride and sulfur hexafluoride are possible due to the fact that their central atoms form covalent bonds with more than four other atoms, ...
19
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3answers
9k views

Why are pi bonds only formed when sigma bonds are formed?

While studying about bonding there was one statement that "pi bonds can only be formed only with sigma bonds" as we know that in double bond there is 1 sigma bond and 1 pi bond but then one question ...
19
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3answers
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Why is one lobe of an sp3 hybridized orbital smaller than its other half?

A hybrid sp3 orbital is drawn with one lobe smaller than its other half, the latter which is of equal size when drawing the p orbital. Why is it so?
4
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2answers
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Can a s orbital overlap with any p orbital to form a sigma bond?

In internet resources, only $p_z$ orbitals are shown to overlap with $s$ orbitals to form sigma bond. But my teacher says that according to Valence Bond Theory, $s$ orbital overlaps with all three $...
1
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1answer
174 views

How to determine the shape of hybridized atomic orbitals in VB theory?

From diagrams, it's rather obvious how $sp$ orbitals are hybridized - the hybrids are just a composite of the $s$ and the $\pm p_{(x)}$ orbitals. However, $sp^2$ orbitals are not just composites of $s,...
8
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3answers
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HCH bond angle in cyclopropane and cyclobutane

I understand why the $\ce{CCC}$ bond angles in cyclobutane and cyclopropane are less than ideal $109.5^\circ$ due to the geometric restrictions they encounter in a cyclic structure. However, it is not ...
4
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1answer
1k views

Why does phosphorus give a free electron in silicon doping?

Extrinsic semiconductors are created by doping an intrinsic semiconductor; typically silicon is doped with phosphorus to create free electrons or boron to create "holes". In the case of phosphorus ...
3
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3answers
165 views

Effect of magnetization on oxidation (rusting) of iron

Can magenetizing a piece of iron bar slow-down (or speed-up) the oxidation (rusting) process? In other words have any influence on it ? From what I've looked up( wikipedia, quora), it appears that the ...
1
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1answer
1k views

Relation between various bond angles of Nitrogen compounds

I was thinking what could be order of bond angles of NH3, NF3, N(CH3)3 and N(C2H5)3. Considering NF3 and NH3: Since there is backbonding between 2p-2p orbitals of N and F, there will be a partial ...
9
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2answers
6k views

Hybrid orbitals forming molecular orbitals

My teacher showed me this diagram on how the hybrid orbitals of two atoms combine to form molecular orbitals. I was confused by this because I thought that VB and MO theories were two separate ...
6
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1answer
185 views

Electronic model with highest prediction rate

Amongst many models, including the valence bond model (VB) or the molecular orbital (MO) model, which are the ones with best predictive power? (e.g. the MO is thought to predict spectroscopic ...
12
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3answers
1k views

Do Li4 or Li8 molecules exist?

I've read that alkali metals form ionic bonds; $\ce{Li}$ is an exception which majorly forms covalent bonds. Wikipedia says dilithium exists. This makes me wonder why $\ce{Li_8}$ doesn't exist. It ...
3
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2answers
683 views

Comparing bond angles in carbonyl dichloride and carbonyl dibromide

Background I was studying VSEPR and hybridization theory and one of the popular questions in many textbooks was comparison of bond angle of $\ce{NH3}$, $\ce{NF3}$ and $\ce{NCl3}$. $\ce{NF3}$ had ...
3
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1answer
379 views

Orbital Electronegativity Considerations in Resonance Structures

After consulting three organic chemistry texts (Wade, Klein, and Brown), only one actually clearly delineates a few guidelines for picking the most significant resonance structure. The others mention ...
5
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1answer
4k views

What Causes Atomic Orbitals to Hybridise?

I'm finding it difficult to visualise the process of hybridisation. Taking the example of formation of $\ce{CH4}$, can it viewed as the collapsing of the p orbitals of the Carbon atoms as they get "...
3
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0answers
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Why are d orbitals used in the hybridisation of PCl5 and similar compounds? [duplicate]

Phosphorus uses its $\ce{3s}$, three $\ce{3p}$ and one $\ce{3d}$ orbitals for its hybridization in $\ce{PCl5}$ and similar compounds. However, shouldn't it use its $\ce{4s}$ rather than $\ce{3d}$ ...
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1answer
8k views

Hybridization of oxygen in Nitrate ion and the location/bond of nitrogen's lone pair

I have tried to apply the rules and basics that I learnt so far. But I am confused about the hybridization of oxygen atoms which are making the single bond in nitrate ion. Following are the steps I ...
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1answer
82 views

What is the difference between resonance and π conjugation

I have seen electron delocalization mentioned frequently in 2 separate contexts: resonance (ozone, carbonate / nitrate...) and π-conjugation systems (aromatic compounds). While the 2 initially sound ...
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1answer
2k views

Difference between valency and oxidation state

I know the abstract and sketchy obscure differences but I cannot find anywhere the specific comparison between the concepts of oxidation states and valency including how they are used to describe ...
0
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1answer
53 views

Why isn't just a fully occupied valence s orbital stable?

Why arent elements like calcium with an electron configuration of $[\text{noble gas}]\ n\mathrm{s}^2$ stable, although all the populated orbitals are fuully filled? Why is it necessary to obtain an ...