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??? _______________________________ 2 LRSVDS CH110 Hyrbrid Orbitals 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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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???
_______________________________
2!LRSVDS! CH110 Hyrbrid Orbitals!
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?!
3!LRSVDS! CH110 Hyrbrid Orbitals!
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. !
4!LRSVDS! CH110 Hyrbrid Orbitals!
Which molecules are
polar?!
5!LRSVDS! CH110 Hyrbrid Orbitals!
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)