Transcript 3-D Shapes of Molecules

Shapes of Molecules
• Determined by number of valence electrons of
the central atom
• 3-D shape a result of bonded pairs and lone
pairs of electrons
• Use VSEPR theory (valence-shell-electron-pair
repulsion
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Using the VSEPR Model
1. Draw the electron-dot structure
2. Identify the central atom
3. Count the total number of electron pairs
around central atom
4. Predict the electron shape
5. Predict the shape of the molecule using the
bonding atoms
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Shapes of Molecules
Number of electron pairs
(= negative charge clouds)
Number of bonded atoms
Angle
2
Name of shape
linear
2
180°
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BeCl2
Be
2 valence electrons
..
:
Cl
..
:
Be
..
..
:
Cl
..
Be
:
Cl
:
..
..
Cl : linear, 180°
..
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More Electron Pairs
Electron Angle
Pairs
3
120°
3
120°
Bonded
Atoms
3
Name of
Shape
trigonal planar
2
angular
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Electron Shape with 3 Pairs
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BF3
B has 3 valence electrons
F
120°
trigonal
planar
B
F
F
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SO2
S has 2 bonded atoms , 1 lone pair (electron cloud)
120°, angular
.. .. ..
:O:: S:O:
..
S
O
O
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More Electron Pairs
Electron Angle
Pairs
4
109°
Bonded
Atoms
4
Name of
Shape
tetrahedral
4
109°
3
pyramidal
4
109°
2
bent, angular
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Tetrahedral CH4
4 electron Pairs, 4 bonded atoms, 109°
H
H
C
H
C
H
H
H
H
H
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NH3 Pyramidal
N has 4 electron pairs, 3 bonded H atoms
Shape is called pyramidal
H
..
: N
..
H
..
: H
N
H
H
H
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H2O Bent or Angular
O has 4 electron pairs, 2 bonded H atoms
Shape is called bent or angular, 109°
..
: O : H
..
H
O
H
H
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Learning Check
Determine the molecular geometry of each of the
following:
A. CCl4
1) tetrahedral
2) pyramidal
3) angular
B. SO3
1) trigonal planar
2) pyramidal
3) angular
C. PCl3
1) trigonal planar 2) pyramidal
3) angular
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Solution
Determine the molecular geometry of each of the
following:
A. CCl4
1) tetrahedral
B. SO3
1) trigonal planar
C. PCl3
2) pyramidal
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