# 0.6 Molecular geometry and electron domain theory  (Page 4/6)

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As an example of a molecule with an atom with less than an octet of valence shell electrons, we consider borontrichloride, $B{\mathrm{Cl}}_{3}$ . The geometry of $B{\mathrm{Cl}}_{3}$ is also given in : it is trigonal planar , with all four atoms lying in the same plane, and all Cl-B-Cl bond angles equal to 120°. The three Clatoms form an equilateral triangle. The Boron atom has only three pairs of valence shell electrons in $B{\mathrm{Cl}}_{3}$ . In applying Electron Domain theory to understand this geometry, wemust place three points on the surface of a sphere with maximum distance between points. We find that the three points form anequilateral triangle in a plane with the center of the sphere, so Electron Domain is again in accord with the observedgeometry.

We conclude from these predictions and observations that the Electron Domain model is a reasonablyaccurate way to understand molecular geometries, even in molecules which violate the octet rule.

## Observation 2: molecules with double or triple bonds

In each of the molecules considered up to this point, the electron pairs are either in single bonds or in lonepairs. In current form, the Electron Domain model does not account for the observed geometry of ${C}_{2}{H}_{4}$ , in which each H-C-H bond angle is 116.6° and each H-C-C bondangle is 121.7° and all six atoms lie in the same plane. Each carbon atom in this molecule is surrounded by four pairs ofelectrons, all of which are involved in bonding, i.e. there are no lone pairs. However, the arrangement of these electron pairs, and thus the bonded atoms,about each carbon is not even approximately tetrahedral. Rather, the H-C-H and H-C-C bond angles are much closer to 120°, theangle which would be expected if three electron pairs were separated in the optimal arrangement, as just discussed for $B{\mathrm{Cl}}_{3}$ .

This observed geometry can be understood by re-examining the Lewis structure. Recall that, although there arefour electron pairs about each carbon atom, two of these pairs form a double bond between the carbon atoms. It is tempting to assumethat these four electron pairs are forced apart to form a tetrahedron as in previous molecules. However, if this were thiscase, the two pairs involved in the double bond would be separated by an angle of 109.5° which would make it impossible forboth pairs to be localized between the carbon atoms. To preserve the double bond, we must assume that the two electron pairs in thedouble bond remain in the same vicinity. Given this assumption, separating the three independent groups of electron pairs about a carbon atom produces an expectation that all three pairs should liein the same plane as the carbon atom, separated by 120° angles. This agrees very closely with the observed bond angles. Weconclude that the our model can be extended to understanding the geometries of molecules with double (or triple) bonds by treatingthe multiple bond as two electron pairs confined to a single domain . It is for this reason that we refer to the model as Electron Domain theory.

Applied in this form, Electron Domain theory can help us understand the linear geometry of $C{O}_{2}$ . Again, there are four electron pairs in the valence shell of thecarbon atom, but these are grouped into only two domains of two electron pairs each, corresponding to the two C=O double bonds.Minimizing the repulsion between these two domains forces the oxygen atoms to directly opposite sides of the carbon, producing alinear molecule. Similar reasoning using Electron Domain theory as applied to triple bonds correctly predicts that acetylene, $HCCH$ , is a linear molecule. If the electron pairs in the triple bond aretreated as a single domain, then each carbon atom has only two domains each. Forcing these domains to opposite sides from oneanother accurately predicts 180° H-C-C bond angles.

Is there any normative that regulates the use of silver nanoparticles?
what king of growth are you checking .?
Renato
What fields keep nano created devices from performing or assimulating ? Magnetic fields ? Are do they assimilate ?
why we need to study biomolecules, molecular biology in nanotechnology?
?
Kyle
yes I'm doing my masters in nanotechnology, we are being studying all these domains as well..
why?
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?
research.net
kanaga
sciencedirect big data base
Ernesto
Introduction about quantum dots in nanotechnology
what does nano mean?
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?
absolutely yes
Daniel
how to know photocatalytic properties of tio2 nanoparticles...what to do now
it is a goid question and i want to know the answer as well
Maciej
Abigail
for teaching engĺish at school how nano technology help us
Anassong
Do somebody tell me a best nano engineering book for beginners?
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
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
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?
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 ?
for screen printed electrodes ?
SUYASH
What is lattice structure?
of graphene you mean?
Ebrahim
or in general
Ebrahim
in general
s.
Graphene has a hexagonal structure
tahir
On having this app for quite a bit time, Haven't realised there's a chat room in it.
Cied
what is biological synthesis of nanoparticles
how did you get the value of 2000N.What calculations are needed to arrive at it
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