<< Chapter < Page Chapter >> Page >

Figure 3

Figure 3 is an example of a complete phase diagram. This diagram shows for each temperature and pressure which phase or phases are present at equilibrium. Figure 3 is for water, but each substance has its own unique phase diagram, similar in appearance.

Observation 3: boiling points and intermolecular forces

Earlier in this study, we determined that the boiling point of a liquid is the temperature at which the vapor pressure of the liquid equals the pressure applied externally, e.g. by the atmosphere or by a piston trapping the liquid and gas in a cylinder. When the applied pressure is 1 atm, we refer to this as the “normal boiling point.” If we compare the normal boiling points of two liquids, the liquid with the higher normal boiling point clearly requires a higher temperature to reach a vapor pressure of 1 atm. From our work on dynamic equilibrium, we know that this higher temperature is required to provide sufficient kinetic energy for the molecules in the liquid to overcome stronger attractions between the molecules. Overcoming these attractions is necessary for a molecule to “escape” the liquid and join the vapor phase.

This line of reasoning means that, when we compare the normal boiling points of two liquids, we are also indirectly comparing the strengths of the intermolecular attractions in those two liquids. The liquid with a higher boiling point has stronger intermolecular attractions.

What determines the strength of these attractions? To find out, we can analyze experimental data for the boiling points of many liquids and look at the properties of the corresponding molecules. A useful set of compounds to look at are the covalent compounds formed by combining hydrogen with each of the elements in the “main group,” Groups IV to VII. For example, in the first row of the periodic table, these include CH 4 , NH 3 , H 2 O, and HF. Table 1 gives the experimentally observed normal boiling points of the sixteen hydrides from Groups IV to VII in the first four rows of the periodic table.

Boiling Point (˚C)
CH4 -164
NH3 -33
H2O 100
HF 20
SiH4 -111.8
PH3 -87.7
H2S -60.7
HCl -85
GeH4 -88.5
AsH3 -55
H2Se -41.5
HBr -67
SnH4 -52
SbH3 -17.1
H2Te -2.2
HI -35

At first glance, the values of the boiling points seem to be all over the place. Any patterns that might exist are not obvious. But there are patterns if we look at the data long enough, and those patterns can reveal to us what determines the intermolecular attractions. First, we can see that, for the compounds in each row of the periodic table, the compound with the lowest boiling point is from Group IV: CH 4 , SiH 4 , GeH 4 , and SnH 4 . Note that these are not the lowest four boiling points in Table 1. Rather, for each period, they are lowest boiling points of the compounds in each period. Notice also that the boiling points increase as we move down the table in Group IV, so that the heavier mass molecules have higher boiling points. This is easiest to see if we put them together on a chart in Figure 4.

These two observations suggest that we might find patterns if we put all of the sixteen hydrides on a chart together, sorted by the period each are in. The result is shown in Figure 5, which is just Figure 4 expanded to show all four groups in the data set of Table 1. With this chart, we see that the two patterns we described for Group IV work for Groups V to VII, but we also see three dramatic exceptions to those patterns in H 2 O, NH 3 , and HF.

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
Privacy Information Security Software Version 1.1a
Got questions? Join the online conversation and get instant answers!
Jobilize.com Reply

Get the best Algebra and trigonometry course in your pocket!

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
Google Play and the Google Play logo are trademarks of Google Inc.

Notification Switch

Would you like to follow the 'Concept development studies in chemistry 2013' conversation and receive update notifications?