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

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1answer
27 views

How many empty orbitals do elements have?

A student was contemplating a question regarding elements with "no empty valence orbitals." An argument was made that elements all have infinite number of valence orbitals. Every atom basically ...
7
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1answer
80 views

Why is there sulfur in black powder / gun powder?

Black powder is composed of charcoal, sulfur and a nitrate salt. The charcoal and sulfur serve as fuel and the nitrate is the oxidizing agent. However, wouldn't it be cheaper to leave out the ...
3
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1answer
58 views

Energetic Placement of Atomic Orbitals in the HCl Molecular Orbital Diagram

How are the 3p orbitals of chlorine lower in energy than the 1s orbital of hydrogen?
1
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1answer
64 views

Hybridization in PH3

Does $\ce{PH3}$ exhibit $\ce{sp^3}$ hybridization? Arguments against hybridization: $\ce{PH3}$ is less basic than $\ce{NH3}$. This jibes with the supposition that $\ce{PH3}$ keeps its lone pair ...
4
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1answer
73 views

IBrF2 - van der Waals repulsions - and number of unique bond angles

I understand that the molecule $\ce{IBrF2}$ is T-shaped, with three ligand atoms and two non-bonding pairs. However, how many unique bond angles can this molecule exhibit? My professor argues for ...
6
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2answers
193 views

Are there any full worked examples of DFT calculations?

I just started learning DFT and now I am totally confused. Assuming I want to use B3LYP: \begin{align} v_s\left(\textbf{r}\right) &= v_\text{ext}\left(\textbf{r}\right) + \int d^3r\frac{n\left( ...
3
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1answer
27 views

How to obtain product ratio from energy differences via Boltzmann statistics

I am currently calculating some reactions and I would like to express the ratio of the products in per cents. I am using the Boltzmann statistic in the following way: The probability $p_j$ of a ...
6
votes
3answers
165 views

Do filled Orbitals also hybridize?

Recently I was watching a video on Valence Bond Theory, on the MIT Open-Course youtube channel. The teacher there said that for hybridization to occur, electron promotion from fully filled orbitals to ...
9
votes
1answer
139 views

When is it true that more nodes equals higher energy?

Consider all the MOs of some isolated molecule. (It could be a single atom too; I'll use MO to refer to AOs as well.) Number them in increasing order of the number of nodes (node = surface where the ...
4
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0answers
65 views

What stable arrangements of hydrogen-bonded water exist in the range of 4-20 water molecules?

Water clusters made up of various numbers of water molecules have been described. Are all of these structures theoretical? What experimental evidence supports any of these structures? How does the ...
0
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0answers
31 views

Schrödinger equation and wave function

What is the Schrödinger wave equation? What are radial probability functions, nodes-angular and radial and electron cloud? I am really confused with all these terms and all my book seems to offer me ...
1
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1answer
51 views

Molecular orbitals and “generalized” aufbau principle for heteronuclear molecular configurations

Is there any general ordering or rule for heteronuclear molecules like $\ce{AX_2}$, $\ce{AX_{n}}$, and their molecular bonding/antibonding configurations ($\sigma/\pi$ orbitals) accordingly to some ...
6
votes
1answer
121 views

How to make approximation of rotational partition function of diatomic linear molecules?

Using the rigid rotor approximation to the level energies, and such other appropriate assumptions, we can approximate rotational partition function, $Q_{\mathrm{rot}}$, of linear molecules as follows: ...
0
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2answers
55 views

Theoretical principles of molecular simulations

I am pharmacy student and would like to work in the field of drug design. We learn to work with the programs but thats not enough for me. I want to learn the theoretical principles of computational ...
2
votes
1answer
99 views

Why is N₂ stable but HCN and C₂H₂ unstable?

Compounds with triple bonds generally seem to be unstable. $\ce{HCN}$ and $\ce{C2H2}$ are high-energy, relatively short-lived molecules that will readily polymerise or react with other organic ...
0
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1answer
35 views

square planar geometry in metal complex

I don't understand what this statements wants to say, "Square planar geometry is favoured by ligands that can form pi bonds by accepting electrons from metal atoms or ions" How is this possible I ...
4
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2answers
160 views

Is there any emerged master principle in chemistry, like the theory of evolution in biology?

The question is about emergence and reductionism. Except a few exceptions such as dark matter, most phenomenon in nature could be reproduced from the standard model and general relativity up to a ...
1
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0answers
17 views

Cumulative Problem: Leak in the air conditioning system

A leak in the air conditioning system of an office building releases 12k of $CHF_2Cl$ per month. If the leak continues, how many kilograms of $Cl$ will be emitted into the atmosphere each year? My ...
2
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1answer
27 views

Number of collisions of particles in a box (or a sphere)

Imagine you randomly spread in a cubic space of volume $m^3$ (or in a sphere of volume $V_s$, as you prefer), $n_A$ particles $A$ and $n_B$ particles $B$. Particles $A$ are spheres of volume $V_A$ and ...
4
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1answer
64 views

Magical reaction tanks

I would be interested to know people's opinion on the following matter. Background Often, when the far-from equilibrium behaviour of a chemical reaction system is analysed mathematically (in papers ...
8
votes
2answers
122 views

Relationship between magnitudes of forward and reverse kinetic rate constants

Consider the reversible unimolecular reaction: $A \overset{k_{1}}{\underset{k_{2}}{\rightleftharpoons}} B$ We know that the forward reaction is often considerably more thermodynamically favourable ...
4
votes
1answer
127 views

What's the difference between PBE and B3LYP methods?

I can't find an answer to that question. I was told that in B3LYP, more variables implemented in the method are empirical, but I can't find anywhere if it's true, and I'm sure it's not the only ...
1
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0answers
24 views

TiO2 nanotube application in cement

I am perparing for a presentation on the application of TiO2 nanotubes in cement which is a recent topic in cement chemistry. Do you happen to have any papers (or know of any accessible on Internet) ...
2
votes
2answers
64 views

Semi-Infinite Potential Square Well: Negative Potential

I am having trouble with a problem involving a Semi-infinite potential square well: I have written down some notes that I added to the post. I have problems understanding the physical situation. See ...
1
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2answers
38 views

Dipole moment of symmetrical molecules

While studying dipole moment in organic chemistry, I got stuck at a particular statement written in the book : Symmetrical molecules without lone pair of electrons will have $\mu = 0.$ The ...
3
votes
2answers
209 views

Why does cyclopropane give bromine water test?

This question was in my exam and all I could tell was that it is related to high angle strain as the angle is $60^\circ$ in stead of required $109.5^\circ$. No book I have read mentions this. Also, ...
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0answers
125 views

Natural Bond Orbital (NBO) analyses: Physical significance/interpretation of E(2) 'stabilization energy'?

PREFACE: I am no expert on this topic. My questions at the bottom may be off base. I have some experience with symmetry-adapted perturbation theory (SAPT) when it comes to analyzing intermolecular ...
4
votes
1answer
157 views

Rate Constant Units and Eyring Equation

Rearranging the Eyring equation leads to the following: $$ ∆^\ddagger S^\circ = R \ln{\frac{k \times h}{{k_B}{T}}}+\frac{∆^\ddagger H^\circ}{T} $$ where k is the rate constant, h is the Planck ...
2
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0answers
143 views

What is the pKa of the oxonium / hydronium / H3O+ ion?

Although the wikipedia page on Hydronium indicates a pKa of -1.74, I noticed in the discussion of this page that the subject seems debated (cf. http://en.wikipedia.org/wiki/Talk:Hydronium#pKa.3F) ...
1
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1answer
47 views

How to estimate the dielectric constant of a liquid?

Are there any approximate relationships between the (static) dielectric constant of a liquid and properties of the individual molecules? For example, suppose I know the polarizability and dipole ...
3
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0answers
46 views

Correlation Diagram Doesn't Match Selection Rules?

From Miessler's Inorganic Chemistry, 5th edition, there is this correlation diagram for $d^{2}$ in a octahedral field. On the left hand side, if it's not clear, it goes (from lowest to highest): ...
5
votes
1answer
217 views

Why are excited Slater determinants used to describe electron correlation?

Usually the first step in describing the electronic wave function of a molecule or atom is to describe it with a single Slater determinant. I get that this is an independent particle approximation, ...
2
votes
2answers
107 views

How to properly denote imaginary magnitudes of vibrational frequencies

Vibrational frequency computations provide the magnitudes of vibrational frequencies for each vibrational mode of a molecule ($3N-6$ degrees of freedom for non-linear molecules and $3N-5$ for linear ...
1
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1answer
35 views

Polymers with no molecular mass distribution?

What sort of ideal conditions are required - theoretically - to conduct polymerization reactions to make all the macromolecules end up with exactly the same molecular mass, just like the products in ...
0
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1answer
226 views

Software for predicting chemical reactions

I wondered if it was possible to predict the product(s) of a reaction (or even the equilibrium) based on the reactants and the temperature/pressure. I found an answer to a similar question here: ...
2
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0answers
146 views

DFT optimization of a molecule in gaussian and find electrophilic sides [closed]

I am not a pro, but I have some experience with gaussian. For example, I can optimize a structure, calculate the frequency and rotational energies. In the lab I made a nucleophilic substitution ...
4
votes
1answer
218 views

Suggest methods and basis sets for a variety of systems

Please help me with any/all of the cases below. In the following cases, the named method and basis set are not suitable for the chemical systems. Why aren't they? Could you suggest a suitable ...
0
votes
1answer
125 views

Configuration Interaction matrix composition from electronic configurations

The six electronic configurations below could all be found in the matrix elements of the CI matrix at CISD level. How do I construct the 6 x 6 CI matrix composed of these six configurations and which ...
2
votes
1answer
70 views

Equilibrium: Equations with complex roots

I'm studying civil engineer in my first year. We have a course called "General Chemistry". One of the chapters was about chemical balance of a reaction (called equilibrium in English, I think). We got ...
15
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0answers
401 views

Is there a general consensus on the causes of the alpha-effect?

There have been various explanations posited for the $\alpha$-effect. The $\alpha$-effect refers to a phenomenon wherein nucleophiles with lone pairs on atoms adjacent (i.e., in the $\alpha$- ...
2
votes
1answer
69 views

An alternative basis set for analytical computation of two electron integrals

It is well known that the usage of the Gaussian basis set, in contrast to Slater basis set, leads relative simple semi-analytical expressions for the two electron repulsion integral $(ab|cd)$. Could ...
4
votes
3answers
272 views

LCAO (Linear Combination of Atomic Orbitals) and Phases

So when combining atomic orbitals to form molecular orbitals, you can either add the wave functions or subtract them. But at the same time, orbitals can exist in opposite phases (say one lobe of the p ...
4
votes
2answers
351 views

Hybridisation of the Carbon in an Carbanion

Given the carbanion, $ R_3C^- $, the carbon is $ sp^3 $ hybridized unless it is participating in resonance. This is clear from its steric number. In drawing its orbital diagram, however, I am having ...
6
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4answers
7k views

Why are sigma bonds stronger than pi bonds?

Why are sigma bonds stronger than pi bonds?
1
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1answer
77 views

Electrode potentials at interfaces?

My questions relates to the fundamental concept of electrochemistry, more specifically the electrode potentials. 1) First, why is there a potential difference at the interface of two phases? ...
2
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2answers
79 views

Do ions also form special electron configurations? (just as Copper and Chromium do)

Do ions also form special electron configurations? (just as Copper and Chromium do) I know that because copper has 1 electron in its s-orbital (highest) because it wants to have a full d-orbital ...
5
votes
1answer
106 views

Computing of strengthening of pi-interaction

I need some practical advise. What would be the easiest approach to compute strengthening or weakening of pi-interaction in a bond with multipole-bond character. I'm not really fond of going through ...
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2answers
2k views

what is a pseudohalogen/pseudohalide?

What do you mean by a pseudohalogen/pseudohalide and how do you tell whether a molecule/ion is a pseudohalogen/pseudohalide ?
2
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1answer
394 views

What does reaction exothermicity say about the stability of molecules

If a reaction is exothermic it means that the energy state of the products is lower than that of the reactants so this will be the state that 'nature' will naturally strive for. Often you see that ...
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1answer
1k views

Why x in equilibrium calculations can be “ignored”

You don't need to work out anything for me. I am just giving an example so you can explain something to me. For example: $$\ce{ClF3(g) <=> ClF(g) + F2(g)}\\ \ \ K_c=8.77\times10^{-14} \ \ @\ ...