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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

what is the stm
Brian Reply
is there industrial application of fullrenes. What is the method to prepare fullrene on large scale.?
Rafiq
industrial application...? mmm I think on the medical side as drug carrier, but you should go deeper on your research, I may be wrong
Damian
How we are making nano material?
LITNING Reply
what is a peer
LITNING Reply
What is meant by 'nano scale'?
LITNING Reply
What is STMs full form?
LITNING
scanning tunneling microscope
Sahil
how nano science is used for hydrophobicity
Santosh
Do u think that Graphene and Fullrene fiber can be used to make Air Plane body structure the lightest and strongest. Rafiq
Rafiq
what is differents between GO and RGO?
Mahi
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
Rafiq
what is Nano technology ?
Bob Reply
write examples of Nano molecule?
Bob
The nanotechnology is as new science, to scale nanometric
brayan
nanotechnology is the study, desing, synthesis, manipulation and application of materials and functional systems through control of matter at nanoscale
Damian
Is there any normative that regulates the use of silver nanoparticles?
Damian Reply
what king of growth are you checking .?
Renato
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
?
Kyle
yes I'm doing my masters in nanotechnology, we are being studying all these domains as well..
Adin
why?
Adin
what school?
Kyle
biomolecules are e building blocks of every organics and inorganic materials.
Joe
anyone know any internet site where one can find nanotechnology papers?
Damian Reply
research.net
kanaga
sciencedirect big data base
Ernesto
Introduction about quantum dots in nanotechnology
Praveena Reply
what does nano mean?
Anassong Reply
nano basically means 10^(-9). nanometer is a unit to measure length.
Bharti
do you think it's worthwhile in the long term to study the effects and possibilities of nanotechnology on viral treatment?
Damian Reply
absolutely yes
Daniel
how to know photocatalytic properties of tio2 nanoparticles...what to do now
Akash Reply
it is a goid question and i want to know the answer as well
Maciej
characteristics of micro business
Abigail
for teaching engĺish at school how nano technology help us
Anassong
How can I make nanorobot?
Lily
Do somebody tell me a best nano engineering book for beginners?
s. Reply
there is no specific books for beginners but there is book called principle of nanotechnology
NANO
how can I make nanorobot?
Lily
what is fullerene does it is used to make bukky balls
Devang Reply
are you nano engineer ?
s.
fullerene is a bucky ball aka Carbon 60 molecule. It was name by the architect Fuller. He design the geodesic dome. it resembles a soccer ball.
Tarell
what is the actual application of fullerenes nowadays?
Damian
That is a great question Damian. best way to answer that question is to Google it. there are hundreds of applications for buck minister fullerenes, from medical to aerospace. you can also find plenty of research papers that will give you great detail on the potential applications of fullerenes.
Tarell
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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