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Not all triatomic molecules are bent, however. As a common example, C O 2 is a linear molecule. Larger polyatomics can have a variety of shapes, as illustrated in . Ammonia, N H 3 , is a pyramid-shaped molecule, with the hydrogens in an equilateraltriangle, the nitrogen above the plane of this triangle, and a H-N-H angle equal to 107°. The geometry of C H 4 is that of a tetrahedron, with all H-C-H angles equal to 109.5°. (See also .) Ethane, C 2 H 6 , has a geometry related to that of methane. The two carbons arebonded together, and each is bonded to three hydrogens. Each H-C-H angle is 109.5° and each H-C-C angle is109.5°. By contrast, in ethene, C 2 H 4 , each H-C-H bond angle is 116.6° and each H-C-C bond angle is121.7°. All six atoms of ethene lie in the same plane. Thus, ethene and ethane have very different geometries, despite thesimilarities in their molecular formulae.

Molecular structures

We begin our analysis of these geometries by noting that, in the molecules listed above which do not contain double or triple bonds ( H 2 O , N H 3 , C H 4 and C 2 H 6 ), the bond angles are very similar, each equal to or very close tothe tetrahedral angle 109.5°. To account for the observed angle, we begin with our valence shell electron pair sharing model,and we note that, in the Lewis structures of these molecules, the central atom in each bond angle of these molecules contains four pairsof valence shell electrons. For methane and ethane, these four electron pairs are all shared with adjacent bonded atoms, whereasin

ammonia or water, one or two (respectively) of the electron pairs are not shared with any other atom. Theseunshared electron pairs are called lone pairs . Notice that, in the two molecules with no lone pairs, all bond angles are exactly equal to the tetrahedral angle, whereas the bond angles are only close in the molecules with lonepairs

One way to understand this result is based on the mutual repulsion of the negative charges on the valence shellelectrons. Although the two electrons in each bonding pair must remain relatively close together in order to form the bond,different pairs of electrons should arrange themselves in such a way that the distances between the pairs are as large as possible.Focusing for the moment on methane, the four pairs of electrons must be equivalent to one another, since the four C-H bonds areequivalent, so we can assume that the electron pairs are all the same distance from the central carbon atom. How can we positionfour electron pairs at a fixed distance from the central atom but as far apart from one another as possible? A little reflectionreveals that this question is equivalent to asking how to place four points on the surface of a sphere spread out from each otheras far apart as possible. A bit of experimentation reveals that these four points must sit at the corners of a tetrahedron, anequilateral triangular pyramid, as may be seen in . If the carbon atom is at the center of this tetrahedron and the four electron pairs at placed atthe corners, then the hydrogen atoms also form a tetrahedron about the carbon. This is, as illustrated in , the correct geometry of a methane molecule. The angle formed by any two corners of a tetrahedron andthe central atom is 109.5°, exactly in agreement with the observed angle in methane. This model also works well in predictingthe bond angles in ethane.

Questions & Answers

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.
anyone know any internet site where one can find nanotechnology papers?
Damian Reply
sciencedirect big data base
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.
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. OpenStax CNX. Dec 06, 2007 Download for free at http://cnx.org/content/col10264/1.5
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