For questions seeking answers deduced from or composed of theories regarding the chemical substances and about models and methods of theoretical chemistry.

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17 views

A mixture of 10 cm3 of methane and 10 cm3 of ethane was sparked with an excess of oxygen. What is the volume of CO2 gas produced at r.t.p.? [on hold]

In the question they gave the volume of ethane and methane but temperature and pressure is not mentioned, so how can I possibly found the volume at room temperature and pressure of CO2? May be, I did ...
2
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0answers
19 views

Calculating Raman Intensities from Static Raman Activities

Whenever I want to calculate a Raman spectrum, my quantum chemical programs give me Raman scattering activities. As the common Raman spectrum is dependent on the incident wavelength of the used laser ...
4
votes
4answers
383 views

How to calculate the concentration H3O+ in a solution with pH=6.99?

What is the correct way to calculate the concentration $\ce{H3O+}$ in a solution with $\ce{pH}=6.99$? Attempt 1. pH<7, therefore there are only $\ce{H3O+}$ particles in the solution. ...
2
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0answers
39 views

Why is conjugation not possible if there is not present alternate $\pi$ molecules according to MO theory?

I was reading this page at Chemwiki; there they were discussing conjugated-$\pi$ bond. In order to show that conjugation requires alternate double bonding, they cited the example of ...
3
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1answer
34 views

Is it possible to have accumulation of electron density in the inter-nuclear region even if the overlap integral is zero?

Recap: Lately, I've been studying Hückel theory where I learned about the approximation of neglecting all overlaps and making overlap matrix an identity matrix that is $S_{AB}= 0\;_; \;S_{AA}= 1$ or ...
6
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2answers
119 views

How can off-diagonal Hamiltonian matrix elements be nonzero when the overlap matrix is diagonal?

While studying about Hückel theory, I got accustomed to the approximation of making the overlap matrix an identity matrix; that is making the off-diagonal elements zero as $S_{AB}= S_{BA}= 0\;;$ this ...
3
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1answer
56 views

What is the reason behind neglecting & putting the overlap integrals $0$ in Simple Hückel Theory?

This is an excerpt about Simple Hückel Theory from Elements of Physical Chemistry by Peter Atkins: The first step that Hückel took was to ignore the $\sigma$-bonding framework and focus solely on ...
2
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1answer
27 views

What is the significance of Law of Multiple Proportions?

I cannot understand how the Law of Multiple Proportions is significant, or how does it further improve over Law of Conservation of Mass or Law of Definite Proportions. From Wikipedia: If two ...
3
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0answers
39 views

Coordinates for molecules except cartesian and zmatrix

Every program in theoretical chemistry that I know uses different ways of writing their input. The same holds true for writing the geometry of the molecules of interest. But they can all be reduced to ...
5
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1answer
73 views

Should I include solvation in quantum chemical calculations of a simplified protein-ligand interactions?

I am running a B3LYP-D3/6-31+G geometry optimization of a protein-ligand interaction. Well, not quite, I have simplified the protein to four amino acids surrounding the active site, but I keep the ...
4
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2answers
66 views

Do orbital models derive from the solution of the stationary Schrödinger equation?

I know that hydrogen-like atomic orbitals can be seen as a solution of the stationary Schrödinger equation - but what about atoms with more electrons? As I am a pupil and quite uneducated about this ...
3
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1answer
114 views

Suggestions for simulating transport through membranes with Molecular Dynamics (MD) and Monte Carlo (MC)?

I'm intending to perform a simulation of the transport of simple ions or water through perm-selective membranes, using Molecular Dynamics (MD) and/or Monte Carlo (MC). I've read around that, in ...
11
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1answer
117 views

How important is it that geometry be optimized at a high level of theory?

I've been doing research with a computational chemist for a little while now and in one of our projects we are dealing with a rather large system and because I go to a relatively small university, our ...
5
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3answers
66 views

Is there a universal minimum energy state?

I'm imagining this: if everything was separated (even on the nuclear level) and then the parts were recombined so that they were in the lowest possible energy state, do we have any way of knowing what ...
0
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1answer
56 views

Double bond equivalent [duplicate]

The formula for degrees of unsaturation is: $$1+ \frac{1}{2} \sum ( n_i (v_i-2))$$ $v_i$ = valency of atom $n_i$ = number of atoms with that valency Could someone explain how the formula works, ...
12
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2answers
854 views

Protons and the Heisenberg principle

The Heisenberg uncertainty principle implies that it is not possible to calculate the position and velocity of a body at the same time accurately. Electrons follow this principle since their orbitals ...
1
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1answer
85 views

Why do noble gases like Xe and Kr form compounds, despite offending the octet rule?

According to the octet rule noble gases should not form compounds but xenon and krypton form compounds like $\ce{XeF2}$, $\ce{XeF4}$, $\ce{XeOF2}$ and $\ce{KrF2}$ respectively. Why?
10
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1answer
156 views

Is it possible that atoms with 120 protons are possible, but that atoms with 119 protons aren't possible?

We currently know that there are atoms with atomic number up to 118 are possible. Is it possible that atoms with 120 protons are possible, but that atoms with 119 protons aren't possible? Or are ...
5
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1answer
69 views

Non-bonded orbitals in water

General Chemistry perspective: Looking at the molecular orbitals of water, we can see that the oxygen is $sp^3$ hybridized. Oxygen forms two sigma bonds with hydrogens, and there are two lone pair ...
4
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1answer
481 views

Definition of Electronic energy

Using Born-Oppenheimer approximation, we separate the nuclear and electronic parts of the wavefunction, and treat them separately. We include the terms that have direct dependence on the electronic ...
1
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1answer
64 views

Is anything ever proven in science? [closed]

People often say that nothing is proven in science. This is even true of well-supported theories and laws, which can supposedly be proved wrong with future advances in science and technology. ...
1
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0answers
73 views

Predict flame test color?

If you know the composition of any sample of compound, is it possible to predict it's flame test color? For eg, if you can given Sodium Chloride, then without actually doing the flame test, can you ...
0
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1answer
83 views

Why do we excite electrons before hybridisation?

In case of hybridisation like $\mathrm{sp^3}$ hybridisation of carbon or nitrogen why do we excite electrons before hybridisation? Why couldn't we just mix orbitals without exciting electrons?
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0answers
28 views

What is the justification for Ligand Close Packing Model?

The LCP model predicts that nonbonded atom to atom distances remain approximately the same when the central atoms are changed. What is the theoretical justification for this? thanks
6
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2answers
124 views

Freezing all the water on earth with a seed crystal

I was recently reading the satirical, fictional book Cat's Cradle by Kurt Vonnegut. In this book, one of the major subplots is the invention of a mythical polymorph of ice called ice-9 in the book. In ...
10
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2answers
242 views

Better functionals to work with transition metals

My Masters in inorganic chemistry is focused in magnetic properties of transition metals; great part of the work is done with DFT methods using softwares like ORCA and NWChem, but since my University ...
2
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0answers
40 views

What closure relations can we use in molecular modelling?

Following my question here about the BBGKY hierarchy I was wondering does anyone have any experience in using the method outlined. In particular how would I take an equation off the page and for some ...
6
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2answers
2k views

Why is CO practically nonpolar?

This question was in my book. According to me CO should be polar as it should have a dipole moment. But I found that the $\sigma$-electron drift from C to O is almost nullified by the $\pi$-electron ...
10
votes
2answers
727 views

Is Hydrogen Bonding a Type of Dipole Dipole Interaction?

I understand that dipole dipole forces is due to the attraction of the different partials charges of atoms in different molecules due to their different electro-negativities. For hydrogen bonding, ...
4
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1answer
43 views

Plasma creation and condensation

Every chemical has a decomposition temperature. My understanding is that above that temperature molecular bonds are broken. And if we raise the heat high enough then all molecular bonds will break ...
2
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0answers
105 views

kinetic reaction rate greater than extent of reaction for equilibrium

I'm comparing a model with chemistry at equilibrium versus a kinetic one. I take a network of two reactions: methane steam reforming (MSR) and water gas shift (WGS) at 700°C. I calculated extent of ...
10
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1answer
223 views

Analytical solution of the Schrödinger Equation for AB^+ systems

According to Wikipedia, there are not many problems for which the Schrödinger equation can be solved analytically. [1] The $\ce{H2+}$ ion is probably the most complex molecule that can be treated this ...
9
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0answers
67 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
151 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"? ...
18
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6answers
3k 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, ...
9
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2answers
1k 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 ...
11
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2answers
170 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 Hartree-Fock routine in Python ...
9
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2answers
188 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
172 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
1k 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
55 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 ...
6
votes
2answers
186 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 ...
0
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0answers
21 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 ...
12
votes
1answer
80 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
150 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
95 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
74 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
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1answer
67 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 ...
7
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1answer
409 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?
15
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2answers
536 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 ...