<< Chapter < Page Chapter >> Page >


We begin by assuming the central postulates of the Atomic-Molecular Theory . These are:

  • the elements are comprised of identical atoms
  • all atoms of a single element have the same characteristic mass
  • the number and masses of these atoms do not change during a chemical transformation
  • compounds consist of identical molecules formed of atoms combined in simple whole number ratios
. We also assume a knowledge of theobserved natural laws on which this theory is based: the Law of Conservation of Mass , the Law of Definite Proportions , and the Law of Multiple Proportions .


We have concluded that atoms combine in simple ratios to form molecules. However, we don't know what thoseratios are. In other words, we have not yet determined any molecular formulae. In the second table of Concept Development Study #1 , wefound that the mass ratios for nitrogen oxide compounds were consistent with many different molecular formulae. A glance back atthe nitrogen oxide data shows that the oxide B could be N O , N O 2 , N 2 O , or any other simple ratio.

Each of these formulae correspond to different possible relative atomic weights for nitrogen and oxygen. Sinceoxide B has oxygen to nitrogen ratio 1.14 : 1, then the relative masses of oxygen to nitrogen could be 1.14:1 or 2.28:1 or 0.57:1 ormany other simple possibilities. If we knew the relative masses of oxygen and nitrogen atoms, we could determine the molecular formulaof oxide B. On the other hand, if we knew the molecular formula of oxide B, we could determine the relative masses of oxygen andnitrogen atoms. If we solve one problem, we solve both. Our problem then is that we need a simple way to "count" atoms, atleast in relative numbers.

Observation 1: volume relationships in chemical reactions

Although mass is conserved, most chemical and physical properties are not conserved during a reaction. Volume isone of those properties which is not conserved, particularly when the reaction involves gases as reactants or products. For example,hydrogen and oxygen react explosively to form water vapor. If we take 1 liter of oxygen gas and 2 liters of hydrogen gas, by carefulanalysis we could find that the reaction of these two volumes is complete, with no left over hydrogen and oxygen, and that 2 litersof water vapor are formed. Note that the total volume is not conserved: 3 liters of oxygen and hydrogen become 2 liters of watervapor. (All of the volumes are measured at the same temperature and pressure.)

More notable is the fact that the ratios of the volumes involved are simple whole number ratios: 1 liter ofoxygen : 2 liters of hydrogen : 2 liters of water. This result proves to be general for reactions involving gases. For example, 1liter of nitrogen gas reacts with 3 liters of hydrogen gas to form 2 liters of ammonia gas. 1 liter of hydrogen gas combines with 1liter of chlorine gas to form 2 liters of hydrogen chloride gas. These observations can be generalized into the Law of Combining Volumes .

Law of combining volumes

When gases combine during a chemical reaction at a fixed pressure and temperature, the ratiosof their volumes are simple whole number ratios.

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
Privacy Information Security Software Version 1.1a
Berger describes sociologists as concerned with
Mueller Reply
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, General chemistry i. OpenStax CNX. Jul 18, 2007 Download for free at http://cnx.org/content/col10263/1.3
Google Play and the Google Play logo are trademarks of Google Inc.

Notification Switch

Would you like to follow the 'General chemistry i' conversation and receive update notifications?