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Tetrahedral structure of methane

The dotted lines illustrate that the hydrogens form a tetrahedron about the carbon atom.
The same tetrahedron is formed by placing four points on a sphere as far apart from one another as possible.

We conclude that molecular geometry is determined by minimizing the mutual repulsion of the valence shellelectron pairs. As such, this model of molecular geometry is often referred to as the valence shell electron pair repulsion (VSEPR) theory . For reasons that will become clear, extension of this model impliesthat a better name is the Electron Domain (ED) Theory .

This model also accounts, at least approximately, for the bond angles of H 2 O and N H 3 . These molecules are clearly not tetrahedral, like C H 4 , since neither contains the requisite five atoms to form thetetrahedron. However, each molecule does contain a central atom surrounded by four pairs of valence shell electrons. We expect fromour Electron Domain model that those four pairs should be arrayed in a tetrahedron, without regard to whether they are bonding orlone-pair electrons. Then attaching the hydrogens (two for oxygen, three for nitrogen) produces a prediction of bond angles of109.5°, very close indeed to the observed angles of 104.5° in H 2 O and 107° in N H 3 .

Note, however, that we do not describe the geometries of H 2 O and N H 3 as "tetrahedral," since the atoms of the molecules do not form tetrahedrons, even if the valence shell electron pairs do. (It isworth noting that these angles are not exactly equal to 109.5°, as in methane. These deviations will be discussed later .)

We have developed the Electron Domain model to this point only for geometries of molecules with four pairs ofvalence shell electrons. However, there are a great variety of molecules in which atoms from Period 3 and beyond can have morethan an octet of valence electrons. We consider two such molecules illustrated in .

More molecular structures

First, P Cl 5 is a stable gaseous compound in which the five chlorine atoms are each bonded to the phosphorous atom. Experiments reveal that thegeometry of P Cl 5 is that of a trigonal bipyramid : three of the chlorine atoms form an equilateral triangle with the P atom in the center, and theother two chlorine atoms are on top of and below the P atom. Thus there must be 10 valence shell electrons around the phosphorousatom. Hence, phosphorous exhibits what is called an expanded valence in P Cl 5 . Applying our Electron Domain model, we expect the five valenceshell electron pairs to spread out optimally to minimize their repulsions. The required geometry can again be found by trying toplace five points on the surface of a sphere with maximum distances amongst these points. A little experimentation reveals that thiscan be achieved by placing the five points to form a trigonal bipyramid. Hence, Electron Domain theory accounts for the geometryof P Cl 5 .

Second, S F 6 is a fairly unreactive gaseous compound in which all six fluorineatoms are bonded to the central sulfur atom. Again, it is clear that the octet rule is violated by the sulfur atom, which musttherefore have an expanded valence. The observed geometry of S F 6 , as shown in , is highly symmetric: all bond lengths are identical and all bond angles are90°. The F atoms form an octahedron about the central S atom: four of the F atoms form a square with the S atom at the center, and the othertwo F atoms are above and below the S atom. To apply our Electron Domain model to understand this geometry, we must place six points,representing the six electron pairs about the central S atom, on the surface ofa sphere with maximum distances between the points. The requisite geometry is found, in fact, to be that of anoctahedron, in agreement with the observed geometry.

Questions & Answers

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
what does nano mean?
Anassong Reply
nano basically means 10^(-9). nanometer is a unit to measure length.
Bharti
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
Daniel
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
Maciej
characteristics of micro business
Abigail
for teaching engĺish at school how nano technology help us
Anassong
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
NANO
what is fullerene does it is used to make bukky balls
Devang Reply
are you nano engineer ?
s.
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.
Tarell
what is the actual application of fullerenes nowadays?
Damian
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.
Tarell
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.
Virgil
is Bucky paper clear?
CYNTHIA
carbon nanotubes has various application in fuel cells membrane, current research on cancer drug,and in electronics MEMS and NEMS etc
NANO
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.
Harper
Do you know which machine is used to that process?
s.
how to fabricate graphene ink ?
SUYASH Reply
for screen printed electrodes ?
SUYASH
What is lattice structure?
s. Reply
of graphene you mean?
Ebrahim
or in general
Ebrahim
in general
s.
Graphene has a hexagonal structure
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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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