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It turns out that other measurements and calculations reveal that, when present, hydrogen bonding attractions are approximately ten times stronger than dipole-dipole attractions or dispersion forces, for comparably sized molecules. Thus, hydrogen bonding dominates intermolecular attractions for those molecules which are capable of hydrogen bonding.

Of course, these conclusions are based on the set of data in Table 1 and Figure 5. These sixteen molecules are all somewhat comparable, consisting of no more than 5 atoms, and no more than one atom other than hydrogen. The boiling points of other molecules can reveal other trends in the strengths of intermolecular attractions. We will take one example to illustrate this. Let’s compare the normal boiling point of H 2 O, 100 ºC, to that of octane (C 8 H 18 ), which is 125 ºC. Octane is symmetric, has no dipole moment, and has no N, O, or F atoms that could hydrogen bond. Therefore, octane molecules attract each other entirely through dispersion forces. And yet, the strength of the attractions between octane molecules is greater than that between water molecules. This reveals that the magnitude of the dispersion force can be dominant in comparing molecules of very different sizes. Dispersion forces can dominate both dipole-dipole interactions in polar molecules, and even hydrogen bonding forces.

Therefore, in attempting to predict which of two molecules might have the stronger intermolecular forces, it is important first to consider first whether the molecules are of comparable sizes or of very different sizes. Provided that the molecules are of comparable size, the dispersion forces should not be too very different. In this case, polar molecules will have stronger intermolecular forces than non-polar molecules, and molecules which exhibit hydrogen bonding will have even stronger intermolecular forces.

Review and discussion questions

  1. In the phase diagram for water in Figure 1, start at the point where T = 60 ºC and P = 400 torr. Slowly increase the temperature with constant pressure until T = 100 ºC. State what happens physically to the water during this heating process.
  2. In the phase diagram for water in Figure 1, start at the point where T = 60 ºC and P = 400 torr. Slowly lower the pressure at constant temperature until P = 80 torr. State what happens physically to the water during this process.
  3. Explain why Figure 1 is both a graph of the boiling point of liquid water as a function of applied pressure and a graph of the vapor pressure of liquid water as a function of temperature.
  4. Using arguments from the Kinetic Molecular Theory and the concept of dynamic equilibrium, explain why, at a given applied pressure, there can be one and only one temperature, the boiling point, at which a specific liquid and its vapor can be in equilibrium.
  5. Using dynamic equilibrium arguments, explain why a substance with weaker intermolecular forces has a greater vapor pressure than one with stronger intermolecular forces.
  6. The vapor pressure of phenol is 400 torr at about 160 ºC, whereas the vapor pressure of dimethyl ether is 400 torr at about -40 ºC. Which of these substances has the greater intermolecular attractions? Which substance has the higher boiling point? Explain the difference in the intermolecular attractions in terms of molecular structure.
  7. In Table 4 and Figure 5, the boiling point of stannane (SnH 4 ) is -52 ºC and the boiling point of phosphine (PH 3 ) is -87.7 ºC. SnH 4 is non-polar and PH 3 is polar. Explain why the boiling point of SnH 4 is nevertheless higher than the boiling point of PH 3 .
  8. Figure 5 shows that the boiling points of the hydrides in the first period are all unexpectedly high, except for methane (CH 4 ). Explain why CH 4 is an exception to this trend.

Questions & Answers

where we get a research paper on Nano chemistry....?
Maira Reply
what are the products of Nano chemistry?
Maira Reply
There are lots of products of nano chemistry... Like nano coatings.....carbon fiber.. And lots of others..
Even nanotechnology is pretty much all about chemistry... Its the chemistry on quantum or atomic level
no nanotechnology is also a part of physics and maths it requires angle formulas and some pressure regarding concepts
Preparation and Applications of Nanomaterial for Drug Delivery
Hafiz Reply
Application of nanotechnology in medicine
what is variations in raman spectra for nanomaterials
Jyoti Reply
I only see partial conversation and what's the question here!
Crow Reply
what about nanotechnology for water purification
RAW Reply
please someone correct me if I'm wrong but I think one can use nanoparticles, specially silver nanoparticles for water treatment.
yes that's correct
I think
Nasa has use it in the 60's, copper as water purification in the moon travel.
nanocopper obvius
what is the stm
Brian Reply
is there industrial application of fullrenes. What is the method to prepare fullrene on large scale.?
industrial application...? mmm I think on the medical side as drug carrier, but you should go deeper on your research, I may be wrong
How we are making nano material?
what is a peer
What is meant by 'nano scale'?
What is STMs full form?
scanning tunneling microscope
how nano science is used for hydrophobicity
Do u think that Graphene and Fullrene fiber can be used to make Air Plane body structure the lightest and strongest. Rafiq
what is differents between GO and RGO?
what is simplest way to understand the applications of nano robots used to detect the cancer affected cell of human body.? How this robot is carried to required site of body cell.? what will be the carrier material and how can be detected that correct delivery of drug is done Rafiq
analytical skills graphene is prepared to kill any type viruses .
Any one who tell me about Preparation and application of Nanomaterial for drug Delivery
what is Nano technology ?
Bob Reply
write examples of Nano molecule?
The nanotechnology is as new science, to scale nanometric
nanotechnology is the study, desing, synthesis, manipulation and application of materials and functional systems through control of matter at nanoscale
Is there any normative that regulates the use of silver nanoparticles?
Damian Reply
what king of growth are you checking .?
What fields keep nano created devices from performing or assimulating ? Magnetic fields ? Are do they assimilate ?
Stoney Reply
why we need to study biomolecules, molecular biology in nanotechnology?
Adin Reply
yes I'm doing my masters in nanotechnology, we are being studying all these domains as well..
what school?
biomolecules are e building blocks of every organics and inorganic materials.
how did you get the value of 2000N.What calculations are needed to arrive at it
Smarajit Reply
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Source:  OpenStax, Concept development studies in chemistry 2013. OpenStax CNX. Oct 07, 2013 Download for free at http://legacy.cnx.org/content/col11579/1.1
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