<< Chapter < Page Chapter >> Page >

As an example of a molecule with an atom with less than an octet of valence shell electrons, we consider borontrichloride, B Cl 3 . The geometry of B 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 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 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, H C C H , 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.

Questions & Answers

how do they get the third part x = (32)5/4
kinnecy Reply
can someone help me with some logarithmic and exponential equations.
Jeffrey Reply
sure. what is your question?
okay, so you have 6 raised to the power of 2. what is that part of your answer
I don't understand what the A with approx sign and the boxed x mean
it think it's written 20/(X-6)^2 so it's 20 divided by X-6 squared
I'm not sure why it wrote it the other way
I got X =-6
ok. so take the square root of both sides, now you have plus or minus the square root of 20= x-6
oops. ignore that.
so you not have an equal sign anywhere in the original equation?
Commplementary angles
Idrissa Reply
im all ears I need to learn
right! what he said ⤴⤴⤴
what is a good calculator for all algebra; would a Casio fx 260 work with all algebra equations? please name the cheapest, thanks.
Kevin Reply
a perfect square v²+2v+_
Dearan Reply
kkk nice
Abdirahman Reply
algebra 2 Inequalities:If equation 2 = 0 it is an open set?
Kim Reply
or infinite solutions?
The answer is neither. The function, 2 = 0 cannot exist. Hence, the function is undefined.
Embra Reply
if |A| not equal to 0 and order of A is n prove that adj (adj A = |A|
Nancy Reply
rolling four fair dice and getting an even number an all four dice
ramon Reply
Kristine 2*2*2=8
Bridget Reply
Differences Between Laspeyres and Paasche Indices
Emedobi Reply
No. 7x -4y is simplified from 4x + (3y + 3x) -7y
Mary Reply
is it 3×y ?
Joan Reply
J, combine like terms 7x-4y
Bridget Reply
how do you translate this in Algebraic Expressions
linda Reply
Need to simplify the expresin. 3/7 (x+y)-1/7 (x-1)=
Crystal Reply
. After 3 months on a diet, Lisa had lost 12% of her original weight. She lost 21 pounds. What was Lisa's original weight?
Chris Reply
what's the easiest and fastest way to the synthesize AgNP?
Damian Reply
types of nano material
abeetha Reply
I start with an easy one. carbon nanotubes woven into a long filament like a string
many many of nanotubes
what is the k.e before it land
what is the function of carbon nanotubes?
what is nanomaterials​ and their applications of sensors.
Ramkumar Reply
what is nano technology
Sravani Reply
what is system testing?
preparation of nanomaterial
Victor Reply
Yes, Nanotechnology has a very fast field of applications and their is always something new to do with it...
Himanshu Reply
good afternoon madam
what is system testing
what is the application of nanotechnology?
In this morden time nanotechnology used in many field . 1-Electronics-manufacturad IC ,RAM,MRAM,solar panel etc 2-Helth and Medical-Nanomedicine,Drug Dilivery for cancer treatment etc 3- Atomobile -MEMS, Coating on car etc. and may other field for details you can check at Google
anybody can imagine what will be happen after 100 years from now in nano tech world
after 100 year this will be not nanotechnology maybe this technology name will be change . maybe aftet 100 year . we work on electron lable practically about its properties and behaviour by the different instruments
name doesn't matter , whatever it will be change... I'm taking about effect on circumstances of the microscopic world
how hard could it be to apply nanotechnology against viral infections such HIV or Ebola?
silver nanoparticles could handle the job?
not now but maybe in future only AgNP maybe any other nanomaterials
can nanotechnology change the direction of the face of the world
Prasenjit Reply
At high concentrations (>0.01 M), the relation between absorptivity coefficient and absorbance is no longer linear. This is due to the electrostatic interactions between the quantum dots in close proximity. If the concentration of the solution is high, another effect that is seen is the scattering of light from the large number of quantum dots. This assumption only works at low concentrations of the analyte. Presence of stray light.
Ali Reply
the Beer law works very well for dilute solutions but fails for very high concentrations. why?
bamidele Reply
how did you get the value of 2000N.What calculations are needed to arrive at it
Smarajit Reply
Privacy Information Security Software Version 1.1a
Got questions? Join the online conversation and get instant answers!
QuizOver.com Reply

Get the best Algebra and trigonometry course in your pocket!

Source:  OpenStax, Concept development studies in chemistry. OpenStax CNX. Dec 06, 2007 Download for free at http://cnx.org/content/col10264/1.5
Google Play and the Google Play logo are trademarks of Google Inc.

Notification Switch

Would you like to follow the 'Concept development studies in chemistry' conversation and receive update notifications?