AP Chemistry - VSEPR
Transcript of AP Chemistry - VSEPR
Chemical Bonding II:Molecular Geometry and Hybridization of Atomic
Orbitals
10.1
Valence shell electron pair repulsion (VSEPR) model:
Predict the geometry of the molecule from the electrostatic repulsions between the electron (bonding and nonbonding) pairs.
AB2 2 0
Class
# of atomsbonded to
central atom
# lonepairs on
central atomArrangement of electron pairs
MolecularGeometry
10.1
linear linear
B B
Cl ClBe
2 atoms bonded to central atom0 lone pairs on central atom 10.1
AB2 2 0 linear linear
Class
# of atomsbonded to
central atom
# lonepairs on
central atomArrangement of electron pairs
MolecularGeometry
VSEPR
AB3 3 0trigonal planar
trigonal planar
10.1
10.1
AB2 2 0 linear linear
Class
# of atomsbonded to
central atom
# lonepairs on
central atomArrangement of electron pairs
MolecularGeometry
VSEPR
AB3 3 0trigonal planar
trigonal planar
10.1
AB4 4 0 tetrahedral tetrahedral
10.1
AB2 2 0 linear linear
Class
# of atomsbonded to
central atom
# lonepairs on
central atomArrangement of electron pairs
MolecularGeometry
VSEPR
AB3 3 0trigonal planar
trigonal planar
10.1
AB4 4 0 tetrahedral tetrahedral
AB5 5 0trigonal
bipyramidaltrigonal
bipyramidal
10.1
AB2 2 0 linear linear
Class
# of atomsbonded to
central atom
# lonepairs on
central atomArrangement of electron pairs
MolecularGeometry
VSEPR
AB3 3 0trigonal planar
trigonal planar
10.1
AB4 4 0 tetrahedral tetrahedral
AB5 5 0trigonal
bipyramidaltrigonal
bipyramidal
AB6 6 0 octahedraloctahedral
10.1
10.1
bonding-pair vs. bondingpair repulsion
lone-pair vs. lone pairrepulsion
lone-pair vs. bondingpair repulsion> >
Class
# of atomsbonded to
central atom
# lonepairs on
central atomArrangement of electron pairs
MolecularGeometry
VSEPR
AB3 3 0trigonal planar
trigonal planar
AB2E 2 1trigonal planar
bent
10.1
Class
# of atomsbonded to
central atom
# lonepairs on
central atomArrangement of electron pairs
MolecularGeometry
VSEPR
AB3E 3 1
AB4 4 0 tetrahedral tetrahedral
tetrahedraltrigonal
pyramidal
10.1
Class
# of atomsbonded to
central atom
# lonepairs on
central atomArrangement of electron pairs
MolecularGeometry
VSEPR
AB4 4 0 tetrahedral tetrahedral
10.1
AB3E 3 1 tetrahedraltrigonal
pyramidal
AB2E2 2 2 tetrahedral bent
H
O
H
Class
# of atomsbonded to
central atom
# lonepairs on
central atomArrangement of electron pairs
MolecularGeometry
VSEPR
10.1
AB5 5 0trigonal
bipyramidaltrigonal
bipyramidal
AB4E 4 1trigonal
bipyramidalSee-Saw
(distorted tetrahedron)
Class
# of atomsbonded to
central atom
# lonepairs on
central atomArrangement of electron pairs
MolecularGeometry
VSEPR
10.1
AB5 5 0trigonal
bipyramidaltrigonal
bipyramidal
AB4E 4 1trigonal
bipyramidalSee-Saw
AB3E2 3 2trigonal
bipyramidalT-shaped
ClF
F
F
Class
# of atomsbonded to
central atom
# lonepairs on
central atomArrangement of electron pairs
MolecularGeometry
VSEPR
10.1
AB5 5 0trigonal
bipyramidaltrigonal
bipyramidal
AB4E 4 1trigonal
bipyramidalSee-Saw
AB3E2 3 2trigonal
bipyramidalT-shaped
AB2E3 2 3trigonal
bipyramidallinear
I
I
I
Class
# of atomsbonded to
central atom
# lonepairs on
central atomArrangement of electron pairs
MolecularGeometry
VSEPR
10.1
AB6 6 0 octahedraloctahedral
AB5E 5 1 octahedral square pyramidal
Br
F F
FF
F
Class
# of atomsbonded to
central atom
# lonepairs on
central atomArrangement of electron pairs
MolecularGeometry
VSEPR
10.1
AB6 6 0 octahedraloctahedral
AB5E 5 1 octahedral square pyramidal
AB4E2 4 2 octahedral square planar
Xe
F F
FF
10.1
Predicting Molecular Geometry1. Draw Lewis structure for molecule.
2. Count number of lone pairs on the central atom and number of atoms bonded to the central atom.
3. Use VSEPR to predict the geometry of the molecule.
What are the molecular geometries of SO2 and SF4?(In SF4, S uses an expanded octet of 10.)
AB2E bent
S
F
F
F F
AB4E
See-Saw(distorted
Tetrahedron)
10.1
SO
OS
OO
Parent shapes for EXn molecules (n = 2-5)
Formula n shape shapes of structures
EX2 2 linear
EX3 3 trigonal planar
EX4 4 tetrahedral
EX5 5 trigonal
bipyramidal
Parent shapes for EXn molecules (n = 6-8)
Formula n shape shapes of structures
EX6 6 octahedral
EX7 7 pentagonal
bipyramidal
EX8 8 square
antiprismatic
Final structures for VSEPR theory.
More final structures for VSEPR.
Dipole Moments and Polar Molecules
10.2
H F
electron richregion
electron poorregion
10.2
10.2
Which of the following molecules have a dipole moment?H2O, CO2, SO2, and CH4
O HH
dipole momentpolar molecule
SO
O
CO O
no dipole momentnonpolar molecule
dipole momentpolar molecule
C
H
H
HH
no dipole momentnonpolar molecule
10.2
Chemistry In Action: Microwave Ovens
Bond Dissociation Energy Bond Length
H2
F2
436.4 kJ/mole
150.6 kJ/mole
74 pm
142 pm
Valence bond theory – bonds are formed by sharing of e- from overlapping atomic orbitals.
Overlap Of
2 1s
2 2p
How does Lewis theory explain the bonds in H2 and F2?
Sharing of two electrons between the two atoms.
10.3
Stop here
Hybridization – mixing of two or more atomic orbitals to form a new set of hybrid orbitals.
1. Mix at least 2 nonequivalent atomic orbitals (e.g. s and p). Hybrid orbitals have very different shape from original atomic orbitals.
2. Number of hybrid orbitals is equal to number of pure atomic orbitals used in the hybridization process.
3. Covalent bonds are formed by:
a. Overlap of hybrid orbitals with atomic orbitals
b. Overlap of hybrid orbitals with other hybrid orbitals
10.4
10.4
Formation of sp2 Hybrid Orbitals
10.4
Formation of sp Hybrid Orbitals
10.4
# of Lone Pairs+
# of Bonded Atoms Hybridization Examples
2
3
4
5
6
sp
sp2
sp3
sp3d
sp3d2
BeCl2
BF3
CH4, NH3, H2O
PCl5
SF6
How do I predict the hybridization of the central atom?
Count the number of lone pairs AND the numberof atoms bonded to the central atom
10.4
10.4
Sigma () and Pi Bonds ()
Single bond 1 sigma bond
Double bond 1 sigma bond and 1 pi bond
Triple bond 1 sigma bond and 2 pi bonds
How many and bonds are in the acetic acid(vinegar) molecule CH3COOH?
C
H
H
CH
O
O H bonds = 6 + 1 = 7
bonds = 1
10.5
Sigma bond () – electron density between the 2 atomsPi bond () – electron density above and below plane of nuclei
of the bonding atoms 10.5
10.5
10.5
Molecular orbital theory – bonds are formed from interaction of atomic orbitals to form molecular orbitals.
O
O
No unpaired e-
Should be diamagnetic
Experiments show O2 is paramagnetic(has UNPAIRED e-)
10.6
MO Theory is NOT in the AP Chemistry Curriculum and will NOT be on the AP exam! This is just a quick overview!
Energy levels of bonding and antibonding molecular orbitals in hydrogen (H2).
A bonding molecular orbital has lower energy and greater stability than the atomic orbitals from which it was formed.
An antibonding molecular orbital has higher energy and lower stability than the atomic orbitals from which it was formed. 10.6
10.6
1. The number of molecular orbitals (MOs) formed is always equal to the number of atomic orbitals combined.
2. The more stable the bonding MO, the less stable the corresponding antibonding MO.
3. The filling of MOs proceeds from low to high energies.
4. Each MO can accommodate up to two electrons.
5. Use Hund’s rule when adding electrons to MOs of the same energy.
6. The number of electrons in the MOs is equal to the sum of all the electrons on the bonding atoms.
10.7
Molecular Orbital (MO) Configurations
bond order = 12
Number of electrons in bonding MOs
Number of electrons in antibonding MOs
( - )
10.7
bond order
½ 1 0½
Delocalized molecular orbitals are not confined between two adjacent bonding atoms, but actually extend over three or more atoms.
10.8
10.6