11-1
CB IV
Molecular Geometry
(VSEPR)
x e– Arrangement
x Atom Arrangement
11-2
VSEPR Model
(valence shell electron pair repulsion)
simple model to predict 3D shape
“e– groups” want to be as far apart as possible
(same as baloon arrangements)
due to same charge repulsion
Ref
10: 7 - 8
valence e–’s occur as “e– pairs”:
x non-bonding pairs (lone pairs)
x “bonding pairs” (= single, double, triple bonds)
x odd e– = “1 pair”
Prob
10: in-text: 10, 11
end: 53 -63 odds
various terminology
“e– pair” = effective pair = e– group
HMWK 6 & 7
VSEPR Principle:
# of e– groups predicts shape
Adv Rdg 10: pp. 403 - 406
11-4
11-10
11-11
11-12
11-13
11-14
11-15
11-16
11-17
11-18
11-19
1.) O3;
Lewis :
11-20
Practice ..
Selected Practice
O
O
O
O
AX2E type for central O
O
O
4.) XeF2;
Lewis :
F
Xe F
e dots omitted on F atoms
F
for central O: electron arrangement: trigonal planar
atom arangement: bent
2.) NH3; Lewis :
H
N
N
H
H
H
F
F
P
F
F
5.) BrF5; Lewis :
F
F
Br
F
F
F
e dots omitted on F atoms
AX4E type for central Br
F
F
AX5 type for central P
F
for central Xe: electron arrangement: trigonal bipyramidal
atom arangement: linear
Note: lone pairs occupy more spacious equatorial positions
for central N: electron arrangement: tetrahedral
atom arangement: trigonal pyramidal
3.) PF5; Lewis :
Xe
H
H
AX3E type for central N
AX2E3 type for central Xe
F
F
P
F
F
Br
F
F
F
F
F
for central P: electron arrangement: trigonal bipyramidal
atom arangement: trigonal bipyramidal
for central Br: electron arrangement: octahedral
atom arangement: square pyramidal