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

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The concept that lone pair electrons produce a greater repulsive effect than do bonded pairs can be used tounderstand other interesting molecular geometries. Sulfur tetrafluoride, $S{F}_{4}$ , is a particularly interesting example, shown in .

Note that two of the fluorines form close to a straight line with the central sulfur atom, but the other two areapproximately perpendicular to the first two and at an angle of 101.5° to each other. Viewed sideways, this structurelooks something like a seesaw.

To account for this structure, we first prepare a Lewis structure. We find that each fluorine atom issingly bonded to the sulfur atom, and that there is a lone pair of electrons on the sulfur. Thus, with five electron pairs around thecentral atom, we expect the electrons to arrange themselves in a trigonal bipyramid, similar to the arrangement in $P{\mathrm{Cl}}_{5}$ in . In this case, however, the fluorine atoms and the lone pair could be arranged in twodifferent ways with two different resultant molecular structures. The lone pair can either go on the axis of the trigonalbipyramid ( i.e. “above” the sulfur) or on the equator of the bipyramid ( i.e. “beside” the sulfur).

The actual molecular structure in shows clearly that the lone pair goes on the equatorial position. This can be understood if weassume that the lone pair produces a greater repulsive effect than do the bonded pairs. With this assumption, we can deduce that thelone pair should be placed in the trigonal bipyramidal arrangement as far as possible from the bonded pairs. The equatorial positiondoes a better job of this, since only two bonding pairs of electrons are at approximately 90° angles from thelone pair in this position. By contrast, a lone pair in the axial position is approximately 90° away from three bondingpairs. Therefore, our Electron Domain model assumptions are consistent with the observed geometry of $S{F}_{4}$ . Note that these assumptions also correctly predict the observeddistortions away from the 180° and 120° angles which would be predicted by a trigonalbipyramidal arrangement of the five electron pairs.

## Review and discussion questions

Using a styrofoam or rubber ball, prove to yourself that a tetrahedral arrangement provides the maximumseparation of four points on the surface of the ball. Repeat this argument to find the expected arrangements for two, three, five,and six points on the surface of the ball.

Explain why arranging points on the surface of a sphere can be considered equivalent to arranging electron pairsabout a central atom.

The valence shell electron pairs about the central atom in each of the molecules ${H}_{2}O$ , $N{H}_{3}$ , and $C{H}_{4}$ are arranged approximately in a tetrahedron. However, only $C{H}_{4}$ is considered a tetrahedral molecule. Explain why these statements arenot inconsistent.

Explain how a comparison of the geometries of ${H}_{2}O$ and $C{H}_{4}$ leads to a conclusion that lone pair electrons produce a greaterrepulsive effect than do bonded pairs of electrons. Give a physical reason why this might be expected.

Explain why the octet of electrons about each carbon atom in ethene, ${C}_{2}{H}_{4}$ , are not arranged even approximately in a tetrahedron.

Assess the accuracy of the following reasoning and conclusions:

A trigonal bipyramid forms when there are five electron domains. If one ED is a lone pair, then the lone pairtakes an equatorial position and the molecule has a seesaw geometry. If two EDs are lone pairs, we have to decide among thefollowing options: both axial, both equatorial, or one axial and one equatorial. By placing both lone pairs in the axial positions,the lone pairs are as far apart as possible, so the trigonal planar structure is favored.

Assess the accuracy of the following reasoning and conclusions:

The Cl-X-Cl bond angles in the two molecules are identical, because the bond angle is determined by the repulsion ofthe two Cl atoms, which is identical in the two molecules.

#### 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
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
Sanket 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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