For questions seeking generalised answers deduced from or composed of theories regarding the chemical reactions involved.

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0answers
4 views

Is there a relationship between viscosity and enthalpy of vaporization?

It would be useful to be able to predict relative evaporation rates of liquids. For small reduced temperatures the heat of vaporization is relatively constant, but it is not one of the more common ...
6
votes
0answers
25 views

Similarities and Differences between Resonance and MCSCF treatments

Recently, there has been a question by Voldemort concerning different resonance structures of $\ce{NCO-}$, requesting an explanation why one resonance structure would be more preferred than another. ...
5
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2answers
80 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"? ...
11
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5answers
259 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, ...
8
votes
2answers
404 views

Is density functional theory an ab initio method?

The following comment by Wildcat made me think about whether density functional theory (DFT) can be considered an ab initio method. @Martin-マーチン, this is sort of nitpicking, but DFT (where the ...
4
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1answer
110 views

Complexity in computing the integrals involving higher angular momentum

I am quite familiar with Hartree Fock theory. However, writing it into program is an entirely different task, and that is where I have a couple of questions. I wrote a HF routine in Python a couple ...
8
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2answers
127 views

Why are real orbitals used to define the orbital of hydrogenic atoms instead of complex orbitals?

On the physics site, I asked the difference between real & complex orbital. Real orbitals are the superposition of complex orbitals having definite magnetic quantum number states. \begin{align} ...
5
votes
1answer
147 views

Electronic density distribution in hydrogen bond

I'm currently studying about the atomic configuration of electrostatic interactions. Concept is there that in case of interactions like in N-H...N-H (amides), the stability depends on the position of ...
6
votes
2answers
445 views

Can the Bohr atomic model be applied to sodium and other single valence electron species?

Is $\ce{Na}$ a single electron species and can I apply Bohr's Model on it? Please explain why not as it also contains one electron in its outermost shell.
-1
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0answers
47 views

Clarification on the significance of negative edges in a graph (Chemical reactions example)? [closed]

I have been looking for a real world example of the significance of negative edges and found a couple of examples (although im still trying to grasp the concept), but one example keeps coming up and ...
-1
votes
1answer
20 views

Cathode rays produce heat when they fall on a matter

I have studied this many times in my Chemistry F.Sc-1 book that cathode rays produce heat when they fall on a matter but this thing is beyond my comprehension that how they produce heat?
6
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2answers
145 views

Why does the quantum number n limit the value of l, and why does l, likewise, limit the value of m?

Any quantum number that represents the size of an orbital is a positive integer, $n$. Any quantum number that represents the shape of an orbital is a non-negative integer, $l : l < n$. Any ...
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0answers
19 views

Is there a theoretically greatest atomic number? [duplicate]

Is there any law of nature/chemistry that would prevent an ideal chemist (i.e. one that knows everything about chemistry and that can synthesize any physically possible chemical element)from ...
11
votes
1answer
76 views

Predicting relative solubilites of salts without Ksp values

Is there a way of comparing which salt is more soluble without knowing their $ K_{sp}$ data or performing experiments? For example, comparing $\ce{Hg2Cl2}$ and $\ce{Cr2(SO4)3}$. I am not sure ...
2
votes
1answer
40 views

Determining the boiling point of a substance with the triple point and critical point

If I have the pressure and temperature of a substance in its triple point, as well as its pressure and temperature in the critical point, how can I determine de boiling point of the substance at 1 atm ...
5
votes
1answer
70 views

Behaviour of element 111

Is element 111 considered to act as an eka-aurum? Being under the same column of group 11, which usually provides enough evidence for correlation of properties for an eka-element, would this element ...
6
votes
1answer
49 views

Collisonally induced intersystem crossing

What makes a molecule a good initiator of collisionally induced ISC? $\ce{N2}$, $\ce{O2}$ and $\ce{CH4}$ have been mentioned as examples. I imagine the most important factor is the ability to quench ...
3
votes
1answer
52 views

Possible Synthesis of a Polymer

Following a question I have asked previously, what I intend to inquire this time is quite similar as well, except, with a polymer. So previously I asked whether such monomer PCDO is possible to ...
6
votes
1answer
303 views

Born-Oppenheimer adiabaticity

Born Oppenheimer aproximation is said to be adiabatic. What does adiabatic mean? What would be the case of a non adiabatic approximation to the Schrödinger equation?
12
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2answers
431 views

Ripping apart a polymer - reaction or not?

I was holding a piece of plastic earlier, and I ripped it in half. This caused me to start to think about what was happening at the atomic level. If the plastic is being ripped, clearly bonds are ...
11
votes
2answers
472 views

For a given element do heavier isotopes form stronger bonds than lighter isotopes?

I know that $\ce{C-D}$ and $\ce{C-T}$ bonds are stronger than $\ce{C-H}$ bonds, but is this generally true for isotopes of all elements? (By isotopes I mean stable ones with large half lives.)
6
votes
2answers
229 views

Exchange-correlation hole

I did a google and chemistry.exchange search and found several technical definitions of the exchange correlation hole. The questions that I want to proposes are: What the exchange-correlation hole ...
8
votes
2answers
129 views

How can the dipole moment of carbon monoxide be rationalised by molecular orbital theory?

Despite the fact that oxygen is much more electronegative than carbon, the bond in $\ce{CO}$ presents a weak dipole moment. This observation can easily be explained using the concept of "dative bond", ...
7
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0answers
52 views

Radiation in space and its effects on chemical reactions?

I know that one current area of research is ways to protect astronauts from ionizing radiation when they venture out of the atmosphere of Earth, but would that same ionizing radiation be a cause of ...
4
votes
1answer
104 views

Theoretical model for the hydrogen bond

I am curious how, from the perspective of quantum chemistry, the hydrogen bond is modeled. In particular I am interested in using such a model to estimate the amount of energy released per $\ce{H2O}$ ...
3
votes
2answers
263 views

What kind of math should I expect in first year chemistry?

The course calendar for my university describes Chem 101 and 102 as "math intensive". However, it doesn't say what kind of math is involved. What kind of math should I expect in first year chemistry? ...
5
votes
1answer
106 views

Acidity of unsaturated five membered ring relative to seven membered analogue

Which of the following is more acidic? The most acidic proton is positioned on the carbon that is at the top of the above drawings (the methylene hydrogens) on each of the two species as ...
4
votes
1answer
38 views

Charge consistency in fragment qm/mm methods

I'm calculating the multipole moments on several fragments of a molecule. What are some procedures to ensure that the charges etc are representative of the complete molecule? How do I ensure I'm not ...
6
votes
1answer
63 views

How could you predict degenerate pi molecular orbitals just knowing what symmetry point group a molecule belongs to?

If you were to apply the Huckel method to some molecules which belonged to, say, $C_{2v}, D_{2h}, $ and $ D_{4h}$, which ones would you expect to have degeneracies? I'm not sure if this is mixing up ...
14
votes
1answer
167 views

What is the relation between surface tension and initial molecular harmonic?

Initial harmonic is measured as Hartree/Bohr^2 ( like IHarmonic=n in Gaussian Software ). As I am from physics background I am used to look at features from their dimension point of view: Actually ...
10
votes
2answers
188 views

Hypervalency and the octet rule

I realize that the octet rule is more a suggestion than a rule, and that it applies mainly to non-transition metal compounds. Still, compounds that don't have an octet, like $\ce{BH3}$, tend to ...
2
votes
1answer
198 views

Why are 2 ways to calculate the energy of the ground state?

Setup I found in Szabo, Quantum chemistry page 88, these two ways to calculate the energy of the ground state: $$E_0= \sum_a^N \langle a|h|a\rangle + \frac{1}{2} \sum_a^N \sum_b^N \langle ...
2
votes
2answers
54 views

Does the third law of thermodynamics apply to all compounds and elements?

According to wikipedia, the third law of thermodynamics is "The entropy of a perfect crystal, at absolute zero (zero kelvins), is exactly equal to zero.". Then, theoretically, could all substances, ...
8
votes
3answers
196 views

How to define custom force in quantum chemistry packages?

I dont know if this is really applicable but I want to add a custom force ( say F(x,y,z) ) to some atoms in my geometry optimization. Is there any way to add such forces to the DFT or Molecular ...
2
votes
1answer
53 views

CASTEP Geometry Optimization Movie

I am using a calculation software called CASTEP, within Materials Studio, and I want to make a "movie" of my geometry optimization, but don't know how to. CASTEP allows one to do many many different ...
7
votes
1answer
60 views

How to visualize or think about spin waves (magnons)?

According to Wikipedia: "A magnon is a quasiparticle, a collective excitation of the electrons' spin structure in a crystal lattice." I have little pictures in my mind for other quasiparticles. For ...
8
votes
1answer
134 views

PBP vs TBP geometry?

Why are the axial bond lengths greater than those of the equatorial bonds in a trigonal bi-pyramid (TBP) geometry molecule; but the opposite is true for pentagonal bi-pyramid (PBP) geometry molecules? ...
5
votes
0answers
114 views

Calculate the number of moles of NO₂ (g) produced per hour per liter of air?

A reaction of importance in the formation of smog is that between ozone and nitrogen monoxide described by $\ce{O3(g) + NO(g)->O2(g) + NO2(g)}$ the rate law for this reaction is: rate of ...
10
votes
2answers
245 views

How to find the second order perturbation to wave function?

Today, I'm looking for how to find the 2nd perturbation to the base in Rayleigh Schrödinger Perturbation Theory (RSPT). SETUP Starting from the 2nd order perturbation in Dirac's notation: ...
2
votes
1answer
70 views

How to get a protein's dihedral angles ordered by variance?

The setting: I want to simulate protein docking and let some dihedral angles vary, but in order to keep it low-dimensional I have to select those which are most likely to change. What I've thought of ...
16
votes
1answer
213 views

What would follow in the series sigma, pi and delta bonds?

I realise, that this question is a stretch, but I was wondering, how would a bonding orbital be called if it was formed from two $f_{x(x^2−3y^2)}$ or $f_{y(3x^2−y^2)}$ orbitals. Have there been any ...
1
vote
1answer
107 views

Is this a possible explanation as to why sigma bonds are stronger than pi bonds?

Sigma bonds form due to the axial overlap of two orbitals whereas pi bonds form due to their lateral overlapping. Since the former is more effective, we can say that sigma is stronger than pi. We mean ...
2
votes
2answers
103 views

Can we really beat the speed of light? [closed]

This is a rather physics question but I wanted to get an insight from a chemistry perspective. I heard from some that you can beat the speed or go faster than it but is that really true. Physicists as ...
4
votes
2answers
414 views

Why are sp hybridized carbocations high energy?

You don’t see carbocations on double bonds very much, and here’s a good reason: compared to sp3, there is more s character in the orbitals, so the empty orbital is held more closely to the ...
6
votes
4answers
149 views

Is there a field of chemistry that doesn't do experiments?

In other words, a field of chemistry that is all theoretical? I have heard of theoretical chemistry, but my chemistry professor said you can't really major in theoretical chemistry. He said the ...
6
votes
2answers
329 views

London dispersion forces and distance relationship

Why is the London dispersion force inversely related to distance but not to the second power but the sixth power? Why is there not an inverse square relationship as there is for Coulombic forces? Is ...
1
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0answers
50 views

Reducing NOx with Ammonia. Practical in a gasifier?

Sorry if this is an outright stupid question. I am no chemist. For nitric oxide: $\ce{2{NH_{3}} + 2 NO -> 2 {N_{2}} + {H_{2}} + 2{H_{2}O}}$ For nitrogen dioxide: $\ce{2{NH_{3}} + 2{NO_{2}} ...
1
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1answer
27 views

What are the possible concentration pathways for a 3-species system?

Inspired by this question, which asks if a multi-species system could oscillate around its equilibrium, I thought about the possible concentration pathways the following more narrow specified system ...
1
vote
3answers
66 views

Why do molecular orbitals in solids merge to bands?

Why do molecular orbitals in solids merge to bands? For example: In silicon every atom is sp3 hybridised, but when I merge two of these orbitals then it yields a bonding and an antibonding MO. When a ...
3
votes
1answer
82 views

Unitary Transformation of the HF equations

I am working on a code to preform a HF procedure and I am a bit confused about the unitary transformation of the basis. My instructions are as follows. specify the basis and geometry (done) ...