What is Intermolecular forces: Definition and 39 Discussions

Intermolecular forces (IMF) (or secondary forces) are the forces which mediate interaction between molecules, including forces of attraction
or repulsion which act between atoms and other types of neighboring particles, e.g. atoms or ions. Intermolecular forces are weak relative to intramolecular forces – the forces which hold a molecule together. For example, the covalent bond, involving sharing electron pairs between atoms, is much stronger than the forces present between neighboring molecules. Both sets of forces are essential parts of force fields frequently used in molecular mechanics.
The investigation of intermolecular forces starts from macroscopic observations which indicate the existence and action of forces at a molecular level. These observations include non-ideal-gas thermodynamic behavior reflected by virial coefficients, vapor pressure, viscosity, superficial tension, and absorption data.
The first reference to the nature of microscopic forces is found in Alexis Clairaut's work Théorie de la figure de la Terre, published in Paris in 1743. Other scientists who have contributed to the investigation of microscopic forces include: Laplace, Gauss, Maxwell and Boltzmann.
Attractive intermolecular forces are categorized into the following types:

Hydrogen bonding
Ionic bonding
Ion–induced dipole forces
Ion–dipole forces
van der Waals forces – Keesom force, Debye force, and London dispersion forceInformation on intermolecular forces is obtained by macroscopic measurements of properties like viscosity, pressure, volume, temperature (PVT) data. The link to microscopic aspects is given by virial coefficients and Lennard-Jones potentials.

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  1. I

    Chemistry Intermolecular forces between NO particles

    The answer is dipole-dipole and London dispersion forces, but I only chose London dispersion forces. How would you determine whether there is a large or small electronegativity difference between N and O? And therefore how would you determine whether the N-O bond is polar covalent or non polar...
  2. jacobtwilliams001

    Intermolecular forces and Transport phenomena

    I am able to find and understand T from kinetic theory, but I do not understand how to use pressure gradient per unit of area and per unit pressure gradient.
  3. Amaterasu21

    B Why don't solids always stick together?

    Hi all, Something I've been wondering - why don't two solid surfaces always stick together when touching each other? As far as I'm aware there are five basic types of solids: Atomic solids: Frozen noble gases containing single atoms held together by London dispersion forces. Molecular...
  4. P

    Chemistry Do ionic compounds have intermolecular forces?

    Homework Statement Do ionic compounds such as NaCl and K2O have intermolecular forces? 2. The attempt at a solution I got stuck conceptually. NaCl and K2O are ionic compounds. Their basic unit is formula units. They are not molecular compounds. Ionic compounds are held together by...
  5. W

    B My Third Post: Change of Intermolecular Distance?

    Hello, Let us imagine a rod resting on a frictionless horizontal surface such that the rod is made up of 2 identical molecules. Let these molecules be named A and B from left to right. If we pull A to the left and B to the right with forces of equal magnitude, the rod must remain at equilibrium...
  6. W

    My First Post: A Contradiction in Simple Free Fall?

    Hello, Let us imagine a solid in a free fall on planet Earth and let us neglect the effect of air resistance on the motion of the solid. According to Newton's Second Law of Motion, since the only force being applied on the solid is its Weight, then its acceleration must be its Weight divided by...
  7. I

    Are chemical messages between proteins intermolecular forces

    This question might be a stretch, but I was just reading about inter- and intra-molecular forces. And I found that "Intermolecular forces (IMFs) are forces of attraction or repulsion which act between neighboring particles (atoms, molecules, or ions)"...
  8. UMath1

    Why Don't Intermolecular Forces Play a Significant Role in CO2 Molecules?

    I understand that due to the geometry of the CO2 molecule it ends up have no net dipole moment. But why doesn't the central carbon atom experience intermolecular forces from the oxygen atoms of other CO2 molecules. What I mean is why can't CO2 form an arrangement where the dipole forces still...
  9. S

    Intermolecular forces and boiling point

    I've come to understand that intermolecular forces cause the boiling point of hydrochloric acid solutions below 20% to be higher than the boiling point of water. I also understand that dissolving hcl in water is an exothermic reaction. But, what about those intermolecular forces. I assume they...
  10. C

    Chemistry Great books on intermolecular forces (physics + chemistry)

    So i want to understand how concepts like van der waals, electronegavity and covalent bonds were discovered, measured and derived back in the days. I'm looking for a good book to explain this. So far I've looked at a book by Jacob.Intermolecular and Surface Forces, Revised Third Edition -...
  11. P

    Intermolecular forces and temperature

    When the temperature of a fixed volume of gas increases (higher average kinetic energy), the effect of intermolecular forces becomes less prominent. That's very intuitive, but how can I understand this in terms of force, velocity, momentum and so on?
  12. B

    Energies of interaction between molecules

    Homework Statement Estimate the energies of interaction at 25 °C between (i) two hydrogen molecules and (ii) two nitrogen molecules, if each pair is separated by 0.3 nm. Explain fully and clearly your reasoning and any assumptions you make in your answer. State the source of the values of any...
  13. J

    What type of intermolecular forces are exhibited in BF3?

    Hi! Boron trifluoride is a nonpolar molecule due to its high symmetry even though the covalent bonds within the molecule are polar. As a result, the only type of intermolecular forces in BF3 would be the London dispersion forces. I understand that these forces are exhibited by nonpolar...
  14. G

    Effects of Intermolecular Forces?

    For a van der Waals gas, there are London dispersion forces causing the gas particles to be attracted to each other while the law of excluded volume provides repulsive forces. How do each of these characteristics effect the pressure, volume, and temperature of the gas? I assumed that for the...
  15. D

    Chemistry Why does Hexane have higher intermolecular force than Propylamine?

    < Moderator Note -- thread moved to Homework Help forums > Shouldn't Propylamine (C3H7NH2) be able to form hydrogen bonds with alike molecules? Hexane (c6h14) doesn't seem to have hydrogen bonding capability.
  16. A

    Why does hydrogen is taken specially in intermolecular forces?

    Though there are other atoms with less electronegativity which can form effective attraction forces,why hydrogen is taken as a speacial case?
  17. S

    Temperature changes and degrees of freedom and intermolecular forces

    Hi I have a couple of questions relating to these topic hope you guys can help :) Comparing ethanol and water, ethanol has weaker intermolecular forces than water. However, it has a greater specific heat capacity by kJ/mol.K than water. Meaning more energy would have to be absorbed per mole of...
  18. K

    What is happning with phase changes and intermolecular forces

    When a substance undergoes a phase change from a solid to a liquid the substance can absorb heat energy without undergoing a temperature change. But I also read that when a substance melts, the atoms absorb energy and thereby vibrate faster, overcoming the intermolecular forces. Temperature is...
  19. Telemachus

    Determination of intermolecular forces using surface tension

    Hi there. I have found the surface tension for liquid etanol on a given problem. Then the problem says: supposing that the coordination number for etanol is 12, what value does the intermolecular interaction energy has? I have ##\gamma=21,26355\frac{dyna}{cm}##, gamma is the surface tension that...
  20. B

    Freezing point depression in terms of intermolecular forces

    Sorry if this is an obvious question...I understand how the justification via the pressure v temp graph works, but I'm not quite understanding freezing point depression in terms of intermolecular forces and temperature. I was taught that due to attractive IMF between solute and solvent particles...
  21. MacLaddy

    Chemistry Intermolecular Forces question

    Homework Statement The question asks to list all the intermolecular forces operating in each of the two liquids. H_2O CH_3OHHomework Equations N/A The Attempt at a Solution I'm mostly getting confused about the London Dispersion Force with water, and London Dispersion Force and...
  22. stevmg

    Name of intermolecular forces of gases

    For a non-ideal gas expanding in a vacuum, the kinetic energy of each of the molecules does NOT remain consant as the gravitational effect of the other molecules would "slow down" these velocities by deceleration. What are those forces referred to? Are they "Newton" forces or what? I can't...
  23. R

    Chemistry Intermolecular forces

    If I have to explain why instantaneous dipole-induced dipole attraction can be greater than permanent dipole- permanent dipole attraction, should I write : 1) It's because for larger molecules, they have higher polarizability, and therefore, so as the instantaneous dipole induced dipole...
  24. K

    Chemistry Determining Intermolecular Forces - Ionic Crystals and Network Solids?

    Homework Statement This is the worksheet: http://webcache.googleusercontent.com/search?q=cache:9jyqtuswY1AJ:www.chemmybear.com/groves/apch13_imfans.doc+ap+chem+pasadena+imf%27s&cd=1&hl=en&ct=clnk&gl=us&client=firefox-a Homework Equations None, as far as I know The Attempt at a...
  25. L

    Chemistry Boiling Points and Intermolecular Forces

    I am given question with a number of compounds such as He, Ne, Cl2, (CH3)2CO, O2, O3 I have to arrange it in increasing/decreasing order of their boiling points. It is related to intermolecular forces i.e London forces, dipole-dipole interactions and also deals with the concepts of...
  26. C

    Chemistry General Chemistry - Intermolecular Forces

    1. Predict which two interactions are stronger than the other two. Check all that apply. [ ] Forces on the picture (a). [ ] Forces on the picture (b). [ ] Forces on the picture (c). [ ] Forces on the picture (d). http://i41.tinypic.com/3wwug.jpg 2. Which member of the following...
  27. K

    After a ligand bonds to a receptor through intermolecular forces

    After a ligand bonds to a receptor through intermolecular forces, how is it unbound and what happens to it after it is?
  28. S

    Chemistry  6 Types of Intermolecular Forces Explained

    Homework Statement I know that there are three types of Intermolecular forces but while searching on the internet I found that there are six intermolecular forces i.e. Dipole-Dipole Interaction, Hydrogen bond, London Dispersion, Ion-Dipole Interaction, Dipole-Induced Dipole Interaction and...
  29. A

    Question about intermolecular forces in gases

    Hi, my question is this. Is a gas with a positive intermolecular potential like a gravity potential in a pendulum? By this I mean if you compress and the expand the gas the force goes from max potential to a minimum ,creating molecular acceleration in the process and then reverses the...
  30. M

    Chemistry  Butane vs Pentane: Which is Liquid & Why?

    Homework Statement There are two compounds, butane and pentane. one is a liquid at at room temp and the other is gas. which is a liquid and why? Homework Equations The Attempt at a Solution I'm guessing that its pentane. For a gas to liquify, it should have a have a higher melting...
  31. M

    Chemistry Intermolecular Forces: Dipole-Dipole, London Dispersion, H Bonding

    what is the strongest intermolecular force, dipole-dipole, london dispersion, or hydrogen bonding. also, how do you know if a molecule is dipole-dipole, london dispersion, or dydrogen?
  32. L

    Chemistry Intermolecular Forces between hexane and iodine

    I am really confused in my advanced chemistry class. We are currently doing intermolecular and intramolecular forces. For example, a book problem that has me frustrated is : "What is the strongest interaction between hexane and iodine?" What's the difference between "dipole-dipole" and...
  33. P

    Capillary forces, intermolecular forces and surface tension questions

    I tried posting a similar question before, however, I've found the 1 reply is actually wrong. Hopefully with better illustrations, someone will know. The situation in the picture is a drop of water entering a capillary tube. It is located here...
  34. K

    Chemistry General Chemistry - Solutions & Intermolecular Forces (HW Help)

    Hi, I need some help with my homework. I have three questions which I'm not quite sure which answer it is, though I give it my best try. If anyone can help, it'll be much appreciated. Thanks in advance... Question One: Which of the following substances will have hydrogen bonds between...
  35. C

    Intermolecular forces > trends in London Dispersion Forces

    My chemistry textbook states the following: "In general, larger molecules tend to have greater polarizabilities because they have a greater number of electrons and their electrons are farther from the nuclei. The strength of the dispersion forces, therefore, tends to increase with increasing...
  36. F

    Chemistry Chemistry-Physical Changes and Intermolecular Forces

    Hi everyone. I have recently just started studying chemistry for my Junior year in High School. So you could say that I am a newbie at this. :smile: I have small knowledge on the relationship between Intermolecular Forces and Physical changes. (Example: Boiling Point.) So if the IMF of a...
  37. M

    Chemistry Comparing Boiling Pts of Bromine & Iodine Monochloride - Intermolecular Forces

    I have been trying to get my head around this question, but do not understand it. Consider the two isoelectronic substances, bromine (Br2) and Iodine monochloride (ICl). Based upon your knowledge of intermolecular forces, explain the difference in their boilings pts. (Bromine: 59 degrees C...
  38. N

    Intermolecular forces problems

    Why the boiling point of HBr will smaller than the Cl2 ? Since the relative molecular mass of HBr is bigger than Cl2 , so the temporary dipole induced dipole forces should be bigger . Thus , the boiling point of HBr should be bigger .
  39. P

    What are the Strongest Intermolecular Forces in these Compounds?

    For the compounds I to VII pick the letter that corresponds to the correct interactions between particles of that particular compound. If more than one type of interaction exists for a compound, pick the letter that corresponds to the strongest interaction. a) Ion-Ion b)...