# 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.

where we get a research paper on Nano chemistry....?
nanopartical of organic/inorganic / physical chemistry , pdf / thesis / review
Ali
what are the products of Nano chemistry?
There are lots of products of nano chemistry... Like nano coatings.....carbon fiber.. And lots of others..
learn
Even nanotechnology is pretty much all about chemistry... Its the chemistry on quantum or atomic level
learn
da
no nanotechnology is also a part of physics and maths it requires angle formulas and some pressure regarding concepts
Bhagvanji
hey
Giriraj
Preparation and Applications of Nanomaterial for Drug Delivery
revolt
da
Application of nanotechnology in medicine
what is variations in raman spectra for nanomaterials
I only see partial conversation and what's the question here!
what about nanotechnology for water purification
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
Nasa has use it in the 60's, copper as water purification in the moon travel.
Alexandre
nanocopper obvius
Alexandre
what is the stm
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?
what is a peer
What is meant by 'nano scale'?
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 ?
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?
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
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