Questions tagged [intermolecular-forces]
The forces, either attractive or repulsive, that exist between molecules due to electric charges or varying electron cloud distribution. This tag could also include intra-molecular attractions (within one molecule itself) often found in a protein amino acid residues.
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Natural Bond Orbital analysis: Significance of stabilization energy determined by 2nd order perturbation
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 ...
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How do non-polar substances dissolve in non-polar solvents?
The case of polar solvents is clear to me - we get an attraction between opposite charges. However, how do non-polar substances dissolve in non-polar solvents? How could it be explained on a molecular ...
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What is the exchange interaction?
As the wikipedia article for the exchange interaction so aptly notes, exchange "has no classical analogue."
How wonderful.
Exchange shows up essentially while enforcing the condition that two ...
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Anomalous boiling point of "iso-" alkanes
I was attempting to compare the boiling points of iso-hexane and 3-methylpentane.
Boiling points of organic compounds depend upon three factors according to Master Organic Chemistry – 3 Trends That ...
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Why are equations of state for a non-ideal gas so elusive?
The ideal gas equation (daresay "law") is a fascinating combination of the work of dozens of scientists over a long period of time.
I encountered Van der Waals interpretation for non-ideal gases ...
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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, ...
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Why do alkanes have higher boiling point than their ether counterparts?
Based on my understanding of intermolecular forces, I expect dipole-dipole interactions to be significantly stronger than van der Waals' interactions. Hence, I expect ethers (which obviously have ...
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Why is the boiling point of fluorine lower than that of oxygen?
Fluorine boils at -188.1 °C and oxygen boils at -183 °C, but shouldn't $\ce{F2}$ boil after $\ce{O2}$?
Despite being electronegative elements, both are nonpolar molecules and posses dispersion forces ...
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Strength of hydrogen bonding in phenol or methanol
I wanted to know whether hydrogen bonding is stronger in phenol or methanol.
I saw on Wikipedia about the enthalpies of hydrogen bonding in various cases.
but could not find the answer to this ...
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Why does HCN boil at a higher temperature than NH3?
The boiling point of ammonia is −33 °C while that of $\ce{HCN}$ is 25 °C. In a recent AP (Advanced Placement) Chemistry test, a free response question asked why this is the case. Can someone shine ...
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Why is the melting point of PCl3 less than that of PCl5?
From just the IB chemistry bonding chapter information, you would normally deduce that $\ce{PCl3}$ and $\ce{PCl5}$ are both covalent molecules.
However, as $\ce{PCl3}$ has a dipole moment, it has ...
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Why are fluoroalkyl chains hydrophobic/oleophobic?
I'm searching for an answer that explains the hydrophobicity / oleophobicity in terms of intermolecular forces, but can't really find one.
Below is an example fluoro-alkyl nano-particle, F-POSS. It ...
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Why does graphite have a high melting point even though its intermolecular forces are weak?
From what I've read online, when a substance undergoes a state change, the intermolecular forces are broken. The covalent bonds are not broken (http://www.bbc.co.uk/schools/gcsebitesize/science/...
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Why doesn't the viscosity of water change much with temperature like it does for other substances?
I would like to know why water doesn't ever become like syrup before it freezes when many other liquids, such as hydrocarbons, seem to have a more gradual change from becoming more viscous and then ...
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Can nonpolar molecules exhibit dipole-dipole forces?
Dipole-dipole forces occur when the positive part of a polar molecule is attracted to the negative part of a polar molecule. In a nonpolar molecule, there may still be polar bonds, it's just that the ...
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How are polarizabilities measured experimentally?
Most common spectroscopies that produce either a full spectrum, a tensor, or a scalar value have a specific instrument associated with them that is relatively self-contained and not custom. For ...
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Help understanding how "steric effects" are distinct from "electronic effects"?
@jakebeal's excellent answer to Why do animal cells “mistake” rubidium ions for potassium ions? includes the following passage:
In the case of potassium versus sodium, which are both very important ...
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Why does the exchange interaction in Hartree-Fock theory lower the total energy?
In Hartree-Fock theory, the expectation value of the total energy can be written as
$$E = \langle\Psi| H |\Psi\rangle = \sum_{a} \langle a| h |a \rangle + \frac{1}{2}\sum_{ab} \big( [aa |bb] - [ab|ba]...
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Why is octane more volatile than water while having a higher boiling point?
Octane has a boiling point of 120 °C. Water has a boiling point of 100 °C. The definition of boiling point is, "the temperature which the liquid substance's saturated vapor pressure equals the ...
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How to identify hydrogen bonds and other non-covalent interactions from structure considerations?
Chemistry is governed by a wide range of interactions, from ionic and covalent bonding, or other types of strong interactions, towards weaker types of bonding, attraction, or repulsion, that typically ...
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Why does silicon tetrafluoride have a higher melting point than sulfur tetrafluoride?
So looking at the Wikipedia pages of sulfur tetrafluoride and silicon tetrafluoride, the melting points are −121 °C and −90 °C respectively, and so $\ce{SiF4}$ has the higher melting point. However, ...
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Dipole-quadrupole polarizability term for induced dipole
For describing an induced dipole, I have usually seen the following equation,
$$
P_{i} = \alpha_{ij}E_{j} + \frac{1}{2}\beta_{ijk}E_{j}E_{k}
$$
where $P_{i}$ is the $i^{\text{th}}$ component of the ...
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Why is the pressure correction in the van der Waals equation proportional to (n/V)^2?
The van der Waals equation for real gases is stated as follows:
$$\left(P + \frac{an^2}{V^2}\right)(V - nb) = nRT$$
For the coefficient $b$, we can reason out that more the number of molecules, the ...
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Why does water weaken ion ion attractions?
My lecturer has told me that water, having a high dielectric value, will "shield" ions and reduce ion-ion attractions.
I really don't see why. Having water molecules surround these two ions ...
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Is an ionic bond more like a covalent bond or an intermolecular force?
I have asked a question loosely asking this, where I confused terms and did not specify what I wanted to know here, so I formed a new question.
What are the differences and similarities between ionic ...
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Possibility of π–π stacking in non-aromatic systems
Is it possible to have π–π stacking for non-conjugated double bond systems?
For example, can the carbonyl groups of two urea molecules participate in π–π stacking? Although urea prefers to stay in ...
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Why is the boiling point of pentane (36.1 °C) slightly higher than that of diethyl ether (34.6 °C)?
Both are chains of the same length, except diethyl ether has an oxygen atom in the middle instead of a carbon. Diethyl ether has a slight dipole from the oxygen atom, so shouldn't the intermolecular ...
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Why are they called ‘dispersion forces’ if they are an attractice force?
From the name, I thought dispersion forces would be repelling or dispersive forces between atoms, and not attractive forces. What is the dispersion part of the name actually referring to? Is it the ...
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Why aren't the Anton computers used more widely?
The Anton computers are purpose-built by DE Shaw research for molecular dynamics simulations. They achieve performance up to an order of magnitude faster than can be achieved with commodity hardware, ...
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Why do molecules having a higher relative molecular mass have stronger inter-molecular forces?
Why do molecules like alkanes with higher relative molecular
mass ($M_\mathrm r$) have stronger intermolecular forces? For example, methane ($\ce{CH4}$) has a weaker intermolecular force than pentane (...
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Which intermolecular interaction is dependent on the inverse cube of distance?
The intermolecular interaction that is dependent on the inverse cube of distance between molecules is:
hydrogen bond
ion-ion interaction
ion-dipole interaction
London force
Inverse ...
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Are buckminsterfullerene-corannulene complexes actually stabilised by π stacking?
According to wikipedia and the references given therein, $\pi\cdots\pi$ stacking interactions are the result of interaction between the quadrupole moments of two aromatic rings, rationalising the ...
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Alkane, alkene, alkyne boiling point comparison
Which of the following has higher boiling points? Alkanes, alkenes, or alkynes? And why?
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Reason for the formation of azeotropes
Why is it that some liquid mixtures (that exhibit positive/negative deviation from Raoult's law) form azeotropic mixtures at certain compositions? What is the physical reason behind this; are there ...
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What's the relationship between Van der Waals forces and hydrophobic interactions?
A question on a past exam for a course I'm studying for asks:
What's the relation between Van der Waals forces and hydrophobic
interactions?
From what I understand, Van der Waals forces are ...
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Can a long polymer chain interact with itself via van der Waals forces?
It is known that van der Waals interaction is an intermolecular forces. So is it possible that a long polymer chain interacting with itself via non-bonded interactions (such as van der Waals forces / ...
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Pressure vs volume plot for real gas and ideal gas
Background
Recently I have been studying about the states of matter and came to the topic of ideal gases and real gases, and the laws related to them. While studying it from my textbook, I saw the ...
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How does intramolecular hydrogen bonding cause the molecules to be separated from each other?
I learnt about intramolecular hydrogen bonding today, which occurs between molecules such as ortho-nitrophenol. What I was told is that in case of intramolecular bonding, the molecules separate from ...
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How to read TINKER's force field parameters
I'm going to parameterize AMBER force field for the simulation of some small molecules. I have found the parameter sets provided by TINKER at here.
I'm stuck here because I couldn't find any ...
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High Viscosity of Noble Gases
Why are the viscosities of noble gases higher than almost all other gases? This seems counter-intuitive since they have much weaker inter-molecular interactions and lower boiling points.
Gas ...
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Why is the boiling point of heavy water higher than normal water?
In class, we learned that London forces become stronger as relative molecular mass increases. Not just in organic chemistry but in things like the halogens.
However, as I understand, the London forces ...
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Van der Waals nonspecific interaction definition
Every definition I see of Van der Waals interactions claim that they are short-range, nonspecific interactions between two chemical species. What does "nonspecific" mean in this context?
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Arrange these compounds: CO2, CH3OH, RbF, CH3Br in order of increasing boiling points
Arrange these compounds: $\ce{CO2}$, $\ce{CH3OH}$, $\ce{RbF}$, $\ce{CH3Br}$ in order of increasing boiling points.
I think I should consider the forces between them, that is:
$\ce{CO2}$: dispersion ...
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At what frequency does a non-polar molecule acquire a dipole able to participate in London Dispersion forces?
London Dispersion forces are forces between non-polar non-ionic molecules that the random fluctuation of their electrons makes them temporarily dipoles.
What is the frequency that this occurs?
Every ...
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How DFT-D3 incorporates coordination number (CN) into C6
I'm reading Grimme's DFT-D3 paper
but really puzzled by how the $\mathrm{CN}$ is considered in the calculation of $C_\mathrm{6}$ coefficients. (Stefan Grimme, Jens Antony, Stephan Ehrlich, and Helge ...
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Why is a ketone not capable of hydrogen bonding among themselves?
The ketone has one oxygen atom in it and there are two lone pairs hanging out, both of which make it seemingly capable of hydrogen bonding. But in reality it is not.
Did some research and found this ...
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Why does tetrachloromethane have a higher boiling point than trichloromethane?
London dispersion forces (LDF) are present in all molecules, whether polar or non-polar. Molecules also exhibiting dipole-dipole interactions (in addition to the LDF) must have stronger forces of ...
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Why do higher-mass isotopes have higher melting and boiling points than lower-mass isotopes?
Different isotopes of the same element have the same number of electrons, so the nature of bonding between different isotopes of the same element should be the same, yet their melting points and ...
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Why do single, double and triple bonds repel each other equal amounts?
I'm here to share with you something that totally confuses me, as I can't see the logic behind it, and my teacher doesn't know either.
Let's take a set of bonds that's trigonal pyramidal, with a lone ...
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What is the underlying chemistry behind the triboelectric effect?
I remember briefly studying the triboelectric effect in Physics but as I now approach the domain of Chemistry, I'd like to know what processes are involved (at the molecular level) when the the ...