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Our understanding of the bonding between atoms in molecules tells us a great deal about the structures and properties of molecules. We can use the valence shell model of atoms and the Lewis model of bonding to explain and even predict what types of molecules will be stable, like CH 4 , and which are not expected to exist, like CH 5 . This is very powerful and quite beautiful. It means that the enormous number of known substances generally fit a fairly simple set of rules that describes their molecules. Without these rules, we would be lost trying to understand the properties of the more than 50 million different substances that chemists have identified. With these rules, though, we cannot only understand the properties of each molecule but even predict the properties of other molecules even if they have never been created before.

Chemistry, though, is about changes in matter. How do substances react with one another? If a molecule is stable under ordinary conditions, why does it become unstable when the temperature is raised or other molecules are added to the flask? We are interested in chemical reactions, but we are also interested in some physical changes which take place in matter. What happens when a substance changes from solid to liquid or liquid to gas? Why do some substances do this so readily?

Answering these questions often requires us to understand how the properties of individual molecules create the properties we see in large quantities of a substance. This seems like a very challenging problem. It is hard enough to think of the structure of one molecule and try to visualize how its structure creates properties such as dipole moments or intermolecular forces. It seems much harder to imagine thinking of a mole of these molecules all interacting with each other at the same time.

We need a way to relate macroscopic properties to molecular properties. As simple examples, let’s compare the substances water, carbon dioxide, and nitrogen. Each of these is composed of molecules with just a few atoms, and all of the atoms have rather small masses, so the molecules all have low molecular weights. These three molecules have very similar molecular properties; however, the physical properties of these three substances are very different. Carbon dioxide and nitrogen are gases at room temperature, but water is a liquid up to 100 °C. We can only get nitrogen to condense by cooling it to -196 °C. This means that the boiling temperatures of water and nitrogen are different by almost 300 °C. Water is a liquid over a rather large temperature range, freezing at 0 °C and boiling at 100 °C. Nitrogen is very different – it is only a liquid between -210 °C and -196 °C. Carbon dioxide is even more interesting. At normal atmospheric pressure, carbon dioxide gas cannot be condensed into a liquid at all, no matter how cold we make it. If we keep cooling carbon dioxide gas to -60 °C, it converts directly to solid “dry ice.” We cannot melt dry ice either. Warming dry ice above -60 °C does not produce any liquid, but instead the solid “sublimes,” meaning that it converts directly into gas.

Questions & Answers

anyone know any internet site where one can find nanotechnology papers?
Damian Reply
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.
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
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
characteristics of micro business
for teaching engĺish at school how nano technology help us
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
what is fullerene does it is used to make bukky balls
Devang Reply
are you nano engineer ?
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.
what is the actual application of fullerenes nowadays?
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.
what is the Synthesis, properties,and applications of carbon nano chemistry
Abhijith Reply
Mostly, they use nano carbon for electronics and for materials to be strengthened.
is Bucky paper clear?
carbon nanotubes has various application in fuel cells membrane, current research on cancer drug,and in electronics MEMS and NEMS etc
so some one know about replacing silicon atom with phosphorous in semiconductors device?
s. Reply
Yeah, it is a pain to say the least. You basically have to heat the substarte up to around 1000 degrees celcius then pass phosphene gas over top of it, which is explosive and toxic by the way, under very low pressure.
Do you know which machine is used to that process?
how to fabricate graphene ink ?
for screen printed electrodes ?
What is lattice structure?
s. Reply
of graphene you mean?
or in general
in general
Graphene has a hexagonal structure
On having this app for quite a bit time, Haven't realised there's a chat room in it.
what is biological synthesis of nanoparticles
Sanket Reply
what's the easiest and fastest way to the synthesize AgNP?
Damian Reply
types of nano material
abeetha Reply
I start with an easy one. carbon nanotubes woven into a long filament like a string
many many of nanotubes
what is the k.e before it land
what is the function of carbon nanotubes?
I'm interested in nanotube
what is nanomaterials​ and their applications of sensors.
Ramkumar Reply
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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