Attention Pay to CAPA HOMEWORK Due DATES
Next test 21 October Chapt 6,7,8
1
Electronegativity
A measure of how strongly the atoms attract electrons in a bond. The bigger the electronegativity difference the more polar the bond.
Cl2
HCl
NaCl
3
Electronegativity and bond type
4
HF
H F Electroneg ativities 2.1 24 1 4.0 4 3
1.9
Difference = 1.9
very polar bond
Compare HF to HCl, HI
HCl
Electronegativities Difference = 0.9
H 2.1
0.9
Cl 3.0
a moderately polar bond
HI
Electronegativities
5
H
0.4
I
2.124 1 2.5 4 3
Difference = 0.4 slightly polar bond
Percent Ionic Character
6
Bond Polarity and Dipole Moment
Isnt a whole charge -just a partial charge + partially positive means partially negative
DEFINE DIPOLE MOMENT
+
d
= xd
H
Cl
The Cl pulls harder on the electrons The electrons spend more time near the Cl
Polar Molecules
Do Polar Bonds Always Lead to Polar Molecules ?
Polar Bonds Have Charge separation in the bond Polar Molecules are Molecules with a positive and a negative end. This Requires things to be true The molecule must contain polar bonds (This can be determined from differences in electronegativity.) Molecular Symmetry can not cancel out the effects of the polar bonds. Must determine molecular geometry to see if this is true.
two
Dipole Moments
Molecules whose centers of positive and negative charge do not coincide, have an asymmetric charge distribution, and are polar.
These molecules have a dipole moment.
The dipole moment has the symbol . is the product of the distance,d, separating charges of equal magnitude and opposite sign, and the magnitude of the charge, q.
10
Are The Following Molecules Polar?
HF CO2 H2O NH3 CCl4
YES NO YES YES NO
Since All Bonds IN These Molecules Are Polar, Polarity Of Molecule Carries Information On Molecular GeometrySymmetry of the Shape
H2O A Very Important Polar Molecule
12
O -----------H Hydrogen Bond Energy Between H2O Molecules 3 - 30 kJ/mol
OH Molecular Covalent Bond Energy in H2O 493 kJ/mol
13
BOILING POINTS- HYDRIDES Strong Hydrogen Bonding Raises Boiling Point of H2O to 100 C
14
HYDROGEN BONDING AND YOUR GENES
As the DNA strands unwind and separate, new complementary strands are produced by the hydrogen bonding of free DNA nucleotides with those on each parent strand. As the new nucleotides line up opposite each parent strand by hydrogen bonding, enzymes called DNA polymerases join the nucleotides by way of phosphodiester links. 15
DNA THE DOUBLE HELIX
A Chip Off the Old Block.
She Has Her Mothers Eyes.
A Spitting Image. Splitting Image.
16
Representations of Molecules
Lewis structures show the number and type of bonds between atoms in a molecule.
All atoms are drawn in the same plane (the paper). Do not usually show the shape of the molecule
17
Representations of Molecules
Lewis structures show the number and type of bonds between atoms in a molecule.
All atoms are drawn in the same plane (the paper). Do not usually show the shape of the molecule
18
VSEPR
Valence Shell Electron Pair Repulsion. Valence shell - outside electrons. Electron Pair repulsion - electron pairs try to get as far away from each other as possible. Predicts three dimensional geometry of molecules, including angles of bonds.
VSEPR
The Valence-Shell Electron-Pair Repulsion Model (VSEPR) Can be used to predict the shape of an ABn molecule when A is a main group element.
ABn
where A = central atom, main group element B = outer atoms n = # of outer atoms
Examples: CO2, H2O, BF3, NH3, CCl4
C
20
VSEPR
VSEPR counts the number of electron domains around the central atom where electrons are likely to be found and uses this number to predict the shape. Electron domains: regions around the central atom where electrons are likely to be found. Two types of electron domains are considered:
bonding pairs of electrons nonbonding (lone) pairs of electrons
21
VSEPR
Electron domains are regions of high electron density Like Charges Repel Each Other- Therefore According to VSEPR, the best arrangement of a given number of electron domains is the one that minimizes repulsions between them. By considering the arrangement that minimizes repulsions between electron domains, we can determine the electron domain geometry - The arrangement of electron domains around the central atom
22
23
24
25
Electron Domain Geometries
You must know You these! must be able to draw these!
26
VSEPR
IMPORTANT!
Molecular geometry is a consequence of electrondomain geometry. BUT --The electron domain geometry is NOT NECESSARILY What We Identify as the shape or molecular geometry of the molecule. BECAUSE The Molecular Geometry is the arrangement of the atoms in space
27
VSEPR
In order to determine the electron domain geometry:
draw the Lewis structure count the total # of electron domains
multiple bonds = 1 electron domain
determine the electron-domain geometry
C
Bonding pairs 28
Four Domains of electrons: Here all electron pairs are shared between two atoms Called Bonding Pairs
4 atoms bonded
Four Bonding Pair Domains Basic shape is tetrahedral, a pyramid with a triangular base. C at center of pyramid Four Total Domains
H C H
Bond Angle 109.5
All four bond angles the same
H
H
VSEPR
Nonbonding (lone) pairs of electrons: electron pairs that are unshared Nonbonding Ammonia Or lonepair
N
3 bonding pairs
30
Three Bonding Pair Domains
Four Total Domains
3 bonded - 1 lone pair
Still basic tetrahedral but no atom bonded to the lone electron pair. Shape is called trigonal pyramidal. N is at apex
H N H H H
N H
H
107.3
2 bonded - 2 lone pairs
Still basic tetrahedral but 2 lone pairs. Shape is called bent
H O H
O H
H
104.5
2 atoms no lone pair on central atom 180
O C O
With three atoms the farthest they can get apart is 180. Shape is linear.
3 atoms no lone pair
Three Bonding Pair Domains Three Total Domains
The farthest the electron pair can be apart is 120. Shape is flat and called trigonal planar.
H
120
C H O
35
VSEPR
Example: Predict the electron domain geometry of IF5. total 42 Valence Electrons
Lewis structure:
F F F I F F
# electron domains: 6
36
VSEPR
Electron domain geometry = octahedral F F F I F F
Molecular geometry = square pyramidal
37
VSEPR
Example: Predict the electron domain geometry of XeF4. total 36 Valence Electrons
Lewis structure:
# electron domains: 6
F-Xe-F F
F
38
VSEPR
Electron domain geometry = octahedral
F I F
F F
Molecular geometry = square planar
39
A Series Based on Octahedral Electron Domain Geometry
40
A Series Based on Trigonal- Bipyramidal Electron Domain Geometry
41
42
VALENCE BOND THEORY Hybrid Orbitals
Combines bonding with geometry
Hybridization
The mixing of several atomic orbitals to form the same total number of hybrid orbitals. the hybrid orbitals that form are identical.
sp
Hybridization
1 s and 1 p orbitals mix to form 2 sp orbitals leaving 2 p orbitals.
sp2 Hybridization
1 s and 2 p orbitals mix to form 3 sp2 orbitals leaving 1 p orbital.
sp3 Hybridization
1 s and 3 p orbitals mix to form 4 sp3 orbitals.
Valence Bond Theory
Two sp hybrid orbitals are formed when one s and one p orbital are hybridized.
NUCLEUS
end up with two lobes 180 apart. Leaves two p orbitals at right angles
45
Linear
Formation of Three sp2 Hybrids
end up with three lobes 120 apart. Leaves one p orbital at right angles
46
triangular planar
Formation of Four sp3 Hybrids
end up with three lobes 109.5 apart. Leaves no p orbitals
tetrahedral
47
Geometry and Hybrids - Summary
linear triangular planar tetrahedral triangular bipyramidal octahedral
48
sp sp2 sp3 sp3d sp3d2
sp hybridization
Leaves two p orbitals at right angles
Allows For Two types of Bonds
Sigma bonds ( bond) from overlap of orbitals along line between atoms Pi bond ( bond) from overlap between adjacent p orbitals above and below atoms
N2
N N
One Sigma Bond and Two Pi Bonds
sp2 hybridization
120
3 sp2 hybrids Three of these in a plane pointing at 120 with respect to each other Leaves one p orbital perpendicular to plane
52
Consider C2H4 (ethylene)
H H C C
H H
The overlap of sp2 orbitals in the plane makes a bond between carbon atoms
sp2 sp2
C
sp2
sp2
sp2
C
sp2
bond
53
C2H4(ethylene) Continued- Add Hydrogen Atoms
H
sp2 sp2
H
C
sp2
sp2
sp2
C
sp2
H
H
Hydrogen atoms make sigma bonds with other sp2 orbitals
54
Where is the P orbital?
Recall the P orbital Perpendicular
The C2H4 Molecule
56
One Sigma And One Pi Bond
Sigma Bond Pi Bond
57
The C2H2 Molecule
58
CO2
CARBON
O C O
Oxygen
C makes two and two O makes one and one
Valence Bond Theory
Hybrid Orbital Set sp sp2 sp3 sp3d sp3d2
60
Electron Domain Geometry linear trigonal planar tetrahedral trigonal bipyramidal octahedral