Know: mean the molecule as - Chemistry Coursescourses.chem.psu.edu/chem110/spring/VanDerSluys/17-18...
Transcript of Know: mean the molecule as - Chemistry Coursescourses.chem.psu.edu/chem110/spring/VanDerSluys/17-18...
1!LRSVDS! CH110 Hyrbrid Orbitals!
Chapter 9 part 2: Polarity in Molecules,
Valence Bond Theory!
Read: ! !BLB 9.3–5!
HW: ! !BLB 9.33, 35, 38 !
! !Packet 9:8-11!
Know: !
bond angles and geometry!
polarity of molecules!
Which Skill Check Test Bonus Deadline is Approaching?? __________________________________
When is EXAM 2???
_______________________________
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Polarity in Molecules!
•" Just because a
molecule possesses
polar bonds does not
mean the molecule as
a whole will be polar.!
Dipole Moment (µ)
•" How can we determine the overall dipole moment for the molecule?!
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Dipole Moment!For a diatomic molecule: µ = Q r
| r | units = debye (D) •!!!• = 3.33 x10-30 C-m +Q -Q
For two charges (+1 and -1) separated by 1 Å
µ = 4.79 D per Å
Where Q = 1.6 x10-19 C = charge of an electron
For a polyatomic molecule: µ depends on:
1.
2. !
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Which molecules are
polar?!
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Dipole Trends in H-X!
HX bondlength Å
µ(exp)D
µ(ionic)D
!EN % ionic
HF 0.92 1.82 4.41 1.9 41%
HCl 1.27 1.08 6.08 0.9 18%
HBr 1.41 0.82 6.75 0.7 12%
HI 1.61 0.44 7.71 0.4 6%
If the H-X bond were ionic, µ(ionic) = Q r
If the H-Cl bond were ionic (r = 1.27 Å ) µ = 4.79 D /Å x 1.27 Å = 6.08 D
However, experimental data show: µ = 1.08 D
Compare the two values: µ(exp) /µ(ionic) x 100 = 1.08/6.08 x 100 = 18%
The bond is only 18% ionic (82% covalent; polar covalent)
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Oxidation Numbers, Formal
Charges, and Partial Charges!
+1 -1 0 0 +" !" H-Cl H-Cl H-Cl " = 0.18
oxidation formal partial charges numbers charges (experimental)
Dipole moment (µ) Measures:
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Polarity of Molecules!
A molecule is polar if there is a NET charge separation between two "ends"
of the molecule: molecule has a negative "end" and a positive "end".
Requirements to have a net dipole: 1."
2.
_________________________________
To determine the polarity of a molecule that has more than 2 atoms:
1."
2."
3."
4." !
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Examples!
CO2 O=C=O electronegativity: C = 2.5 O = 3.5
EPG: MG: bond dipoles? Net dipole moment? _________________________________
CF4
electronegativity: C = 2.5 F = 4.0
EPG: MG:
Bond dipoles? Net dipole moment?!
F
CF
F
F
9!LRSVDS! CH110 Hyrbrid Orbitals!
Examples!
H2O electronegativity: H = 2.1 O = 3.5
EPG: MG: bond dipoles? Net dipole moment? _________________________________
CH3Cl
electronegativity: H = 2.1 C = 2.5 Cl = 3.0
EPG: MG:
Bond dipoles? Net dipole moment?
OH
H
C
Cl
H
HH
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Examples!
NH3
electronegativity: H = 2.1 N = 3.0
EPG: MG: Net dipole moment?
NH
HH
NF
FF
NH3 vs. NF3
µ"= 1.47 D µ = 0.24 D
[electronegativity: H = 2.1 N = 3.0 F = 4.0]
lone-pairs also have small dipoles partial cancellation of bond dipoles in NF3
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Chapter 9 part 3: Valence Bond Theory!
Read: ! !BLB 9.4–6!
HW: ! !BLB 9:43, 47 !
! !Packet 9:13 !
! !!
Know: !
molecular orbitals!
orbital hybridization!
VBT!
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How are bonds made?
Lewis structures: location and number of bonding and lone-pair electrons
VSEPR: spatial distribution of electrons, shape of molecule
How have we described electron distribution in atoms?
What is the electron distribution in molecules?
Molecular Orbitals
Two models:
Valence Bond Theory
Valence orbitals on one atom overlap
with valence orbitals on another atom: this overlap is a covalent bond.
Molecular Orbital Theory a better model that uses wave theory, BUT not
covered in Chem 110 ! [studied in Chem 112 and
organic chemistry] !
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Overlap and Bonding!
•" Covalent bonds formed through the
sharing of electrons by adjacent
atoms.!
•" Only occurs when orbitals on the
two atoms overlap.!
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Overlap and Bonding!
Two forces operating: •" increased overlap of atomic orbitals
(better sharing) brings atoms together
• closer distance between nuclei increases positive-positive charge repulsion
balance of forces ! bond length (0.74 Å for H2)!
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How can atomic orbitals
overlap to form observed
geometries?!
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Bonding in CH4 Carbon ground-state configuration:
Using only open (unpaired) subshell electrons:
Expect:"CH2" molecule 90o bond angles.
What if we “Promote” 2 electrons?
If all subshell electrons participated in bonding, this "CH4" molecule would have:
1. 2. 3. 4.
However, "" Real molecule is tetrahedral "" 109.5o bond angles, "" all bonds are equal length and strength
H
C H
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Bonding Orbitals in Be!
•" Consider beryllium:!
–" No singly-occupied
orbitals!
–" Can’t form Bonds?!
•" Absorb Energy!–" Now form 2 bonds?!
–" Bonds equal?!
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Hybrid Orbitals!•" Mixing the s and p orbitals yields two
degenerate orbitals that are hybrids of the two orbitals.!
–" These sp hybrid orbitals have ____ lobes like a p orbital.!
–" One of the lobes is larger and more rounded as is the s orbital.!
!The sp orbitals are higher in energy than the 1s orbital but lower than the 2p.!
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Hybrid Orbitals on Be!
•" These two degenerate sp orbitals would align themselves 180° from each other.!
•" This is consistent with the observed geometry of beryllium compounds: linear.!
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Hybrid orbitals on B!
Using a similar model for boron leads
to… !
…________ degenerate sp2 orbitals.!
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Hybrid Orbitals on C!
With carbon we get…!
…_____ degenerate sp3 orbitals.!
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Naming Hybrid Orbitals !
NOTE: 1. start with four atomic orbitals
s px py pz
2. end up with four hybrid orbitals
4 sp3
# orbitals name of orbital
Each hybrid orbital is composed of:
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Hybrid Orbitals Using d Orbitals!
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Hybrid Orbitals!
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Deduce the Hybridization from
Molecular Shape!
NH H
H
N
H
H
H
Formula !Structure ! Hybridization!
OH
H
O
H
H
B
F
F
F
F
BF
F