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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

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.
Damian
yes that's correct
Professor
I think
Professor
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
if virus is killing to make ARTIFICIAL DNA OF GRAPHENE FOR KILLED THE VIRUS .THIS IS OUR ASSUMPTION
Anam
analytical skills graphene is prepared to kill any type viruses .
Anam
Any one who tell me about Preparation and application of Nanomaterial for drug Delivery
Hafiz
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
hi
Loga
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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