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Molecular Geometry
How can molecular shapes be predicred using rhe VSEPR rheory?
whv?
'Vhen you^ draw^ a^ Lewis^ structure for^ a^ molecule^ on paper, you^ are making a rwo-dimensional representa-
tion of the atoms. In realiry however, molecules (^) are nor fat-they are three-dimensional. The rrui shape
of a molecule is important because it determines many physical and chemical properties for the substance
In this activity you will learn how to predicr molecular shapes.
Model I (^) - Lewis Structures
Hrco
3 elecrron domains (3 (^) bonding, 0 nonbonding)
3-D Molecular^ Shape
o I\ (^) "-
,d. )
,,"
ri -o
BeF, 2 electron domains (2 (^) bonding, 0 nonbonding)
1s6'
o
CH, 4 electron domains (4 (^) bonding, 0 nonbonding)
o r \oq.:
4'i* o
NH 3 4 electron domains (3 bonding, (^1) nonbonding)
't6.
odij" loa. (^0) H,O 4 electron domains (2 (^) bonding, 2 nonbonding) {t'd' taq.B (-, E-J
Le*n St""ctrer aj I Hr(o
(H,l
. .-.,,_. ....,.H...... .. .....
-5T*----- ..-
i4."NlJ.-
'' (^) -
t]-
H
5+o
H -^
b;(01- --^ -'."H'.... -^ -.^ ."'.'
I I ',1 'l
tor tat .or€t4.
Lone pair (^) = (^) "
co 2 2 electron domains (2 (^) bonding, 0 nonbonding)
I \XJ
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Molecular Geometrv
l. Name the rype of structures shown in (^) the left-hand column of Model 1.
tec*tis Sr'lvnsfi.&t'es
- Examine (^) the drawings in Model 1.
a. V4tat does a solid line between two (^) element symbols represent in rhe drawings (^) of the molecules?
€sv-rc ,. 1fi/'hat^ subatomic particles (protons, (^) neutrons or electrons) make up these (^) solid lines?
eJdrrcpts c tWhat^ does (^) a pair ofdots represent in the drawing ofthe molecules?
Y^'on bordlnl ClcCfrov"tS
. \J, /. What.subaromic particld (protons, (^) neutrons or electrons) makes up each dot? glec$rorrs
- In^ rhe^ English^ language,^ what does the word^ "domain"^ mean? (Your^ group must come to consen- sus on rhis question.)
- \X&ich molecules in Model t have four electron domains? Circle or highlighr the four electron
domains in rhe Lewis strucrure for each molecule that you identified.
3u9,t
- \fhich^ molecules in Model I have two electron domains? Circle or highlight the two electron
domains in the Lewis structure for each molecule rhat you idenrified.
(^) Z,b
- V4rich molecule in Model t has three electron domains? Circle or highlighr the rhree electron
domains in the Lewis srrucrure for the molecule that vou identi6ed.
I
- t^ /hen^ determining the number of electron (^) domains in a Lewis structure, which of the following
should you count? Find evidence from Model 1 ro support your answers.
@nond, on^ the center^ atom^ @I-on. pairs^ on^ the^ cenrer^ arom
Total numbe r of atoms in the molecule
{-on.
c p"in on peripheral atoms ind.ivec*lq becahse^ il a€€ecls fu rru,.nbe,t (^) ef bov'rds
\X/hen determining the number ofelectron domains in a Lewis structure, do you count
double
bonds as one domain or nvo domains? Find evidence ro supporr your answer from Model 1.
ol"r€- donno.irr
+to ov'l{r1 kras^ 2a"on"ejnf o.vrc(^ r't-
ha.t 2 tLo*{att tronds
2
8
POGIL'"' Activities for High School Chemistry
m,.'rs
14. Often we draw Lewis strucrures with 90" bond angles. Do any of rhe molecular shapes in
Model t have (^) 90" bond angles?
15. Are the bond angles in the three-dimensional molecules generally larger or smaller than those
shown in the Lewis structures drawn on notebook paper?
laNqev'
-t
- \X/hy is it possible to get larger angles (^) separating electron domains in three-dimensions versus rwo-dimensions? p;"il;'"e.1^4 ep.es-^ f ^&on t^ I^ beh''"A (^) tfue (^) pa4'ev- I
Identifr the three molecules shown in Model 1 that have four electron domains each.
a. \hat happens (^) to the size ofthe bond angle(s) in a molecule as the number (^) oflone pairs on the central atom increases?
4 L{^5 h&ore [ow-C (^) p..irs '-]? Evlns-{'{"t u&tn- Jr rrv
- Discuss in your group some possible explanations for rhe (^) trend in parr a. Your presenter
should be ready to present to rhe class one or rwo ofyour hyporheses for full class discussion
.lohe (^) patrs {a"k<. ",t,
€sto* (^) S.P"es
To b4^ o.ICI\€^ +a eou,or"t^ fue^ bnd{^ c-nd^ nonbotd,r'n#.-----"-t
I
@
- (^) A student does not "waste" his time drawing a Lewis structure before (^) determining the shape of
PF.. The srudent thinks that the shape of PF, must be trigonal planar because there are three
fluorine atoms bonded to the cenrral phosphorus atom.
a. (^) Draw rhe Lewis structure for PF^.
5t3{.T).3b
!- F
D. (^) 'Vas the s
t'$tr
a'ent\ answer for the shape oFa PF, molecule correct? Explain
Vhy is it (^) important to draw the Lewis srructure for a molecule before idenrifring (^) the shape of the molecule?
F $ f:
tu
c
POGIL'' Activities for High School (^) Chemistry
19. Complete the following chart:
@
Molecule Lewis Structure 3-D Drawing
Name of
3-D Shape
Bond Angle
H 2 S (^) H.B. H ,"b#'.'
) (^) berr* (^) ls"{.8'
PH 1 H. -P -$"f I
H
:"
;E
iaa F:
uo
, CI
"tvlqors-l
PlYenrua^t
[0q'
CCI, ,et^ -d.-eil' I l:
r)
I
o*dt"o
t{$rd.he-'t (^) lrr0 E'
CS c- fr-€ b s--^ "r 6r=6=O^ hreo"r^
aeA
I S{,}
Molecular Geomerry 5
