1. Molecular Polarity
Boiling point = 100 ˚C
Boiling point = -161 ˚C
Why do water and methane differ so much in their boiling points?
Why do ionic compounds dissolve in water?

2. Why do CuCl2, acetic acid, and ethanol dissolve in water?

3. COVALENT BOND (MOLECULES)
FLOW CHART
COVALENT BOND (MOLECULES)
ALL NONMETALS
POLAR
NONPOLAR

4. Polar Molecules
POLAR Molecule have a positive and negative end called POLES
Polar molecules HAVE UNEQUAL SHARING
NONpolar molecules are EQUAL SHARING OF VALENCE ELECTRONS

5. Bond Polarity
Due to the bond polarity, the H—Cl bond energy is GREATER than expected for a “pure” covalent bond.
BOND ENERGY
“pure” bond 339 kJ/mol calc’d
real bond 432 kJ/mol measured
Difference = 92 kJ. This difference is proportional to the difference in ELECTRONEGATIVITY, .

6. Electronegativity, 
 is a measure of the ability of an atom in a molecule to attract electrons to itself.
Concept proposed by
Linus Pauling

7. Some Electronegativity Values for Group A Elements

8. Electronegativity and Bond Types

9. Comparing Nonpolar and Polar Covalent Bonds

10. Bond Polarity
Cl has slight negative charge (-d) H has slight positive charge (+ d)
HCl is POLAR because it has a positive end and a negative end.
Cl has a greater share in bonding electrons than does H.

11. Molecular Polarity
The magnitude of the dipole is given in Debye units.
Named for Peter Debye ( ). Rec’d 1936 Nobel prize for dipole moments.

12. Why are some molecules polar but others are not?
Dipole Moments
Why are some molecules polar but others are not?

13. Molecules—such as HCl and H2O— can be POLAR (or dipolar).
Molecular Polarity
Molecules—such as HCl and H2O— can be POLAR (or dipolar).
They have a DIPOLE MOMENT. The polar HCl molecule will turn to align with an electric field.
Figure 9.15

14. Polar Covalent Bonds share electrons unequally between nonmetal atoms
has an electronegativity difference
range of 0.5 to 1.9
Examples:
Atoms Dipole Type of Bond
Moment
OCl = Polar covalent
ClC = Polar covalent
OS = Polar covalent

15. Bond Polarity Which bond is more polar (or DIPOLAR)? O—H O—F 
OH is more polar than OF

16. Nonpolar Covalent Bonds
equal sharing of electrons between nonmetal
has an electronegativity difference of 0.0 to 0.4
Called dipole moment
Examples:
Atoms Dipole Type of Bond Moment
NN = Nonpolar covalent
ClBr = Nonpolar covalent
HSi = Nonpolar covalent

17. Ionic Bonds electron transfer between metal and nonmetal
has a large electronegativity difference (>2 or more)
Examples:
Atoms Electronegativity Type of Bond
Difference
ClK – 0.8 = Ionic
NNa – = Ionic
SCs 2.5 – 0.7 = Ionic

18. Predicting Bond Types

19. Learning Check
Use electronegativity differences to classify each of the following bonds as nonpolar covalent (NP), polar covalent (P), or ionic (I):
A. K and N
B. N and O
C. Cl and Cl
D. H and Cl
Metal / Non (I)
0.5 (P)
(NP)
(P)

20. F has maximum .
Atom with lowest  is the center atom in most molecules.
Relative values of  determine BOND POLARITY
Electronegativity, 
See Figure 9.9

21. Consequences of H2O Polarity
Microwave oven
Consequences of H2O Polarity

22. Molecules will be polar if
Molecular Polarity
Molecules will be polar if
a) bonds are polar
AND
the molecule is NOT
“symmetric”

23. Nonpolar Molecules A nonpolar molecule
may contain identical atoms (nonpolar bonds)
may have a symmetrical arrangement of polar bonds that cancel dipoles

24. If Symmetric = nonpolar
All below are NOT polar
If Symmetric = nonpolar

25. Determining Molecular Polarity
The polarity of a molecule is determined from its
shape
polarity of the bonds
dipole addition / cancellation

26. Polar Molecules contains polar bonds
has a separation of positive and negative charge called a dipole indicated by a dipole arrow
has dipoles that do not cancel

27. Polar or Nonpolar?
Compare CO2 and H2O.
Which one is polar?

28. CO2 is NOT polar even though the CO bonds are polar.
Carbon Dioxide
CO2 is NOT polar even though the CO bonds are polar.
symmetrical.
+1.5
-0.75

29. Consider AB3 molecules:
Polar or Nonpolar?
Consider AB3 molecules:
BF3, Cl2CO, and NH3.

30. Molecular Polarity, BF3 B atom is positive and F atoms are negative.
B—F bonds in BF3 are polar.
But molecule is symmetrical and NOT polar

31. Molecular Polarity, HBF2
H & F atoms are more electronegative than B.
B—F and B—H bonds both are polar.
NOT symmetrical
= POLAR

32. Methane is symmetrical
Is Methane, CH4, Polar?
Methane is symmetrical
and is NOT polar.

33. Is CH3F Polar?
C—F bond is very polar.
NOT symmetrical
= POLAR.

34. Substituted Ethylene POLAR.
C—F bonds are MUCH more polar than C—H bonds.
(HYDROCARON = NON)
both C—F bonds are on same side of molecule = ASYMMETRIC
POLAR.

35. Substituted Ethylene NOT POLAR.
C—F bonds are MUCH more polar than C—H bonds.
HOWEVER both C—F bonds are on opposite ends so molecule is symmetric
NOT POLAR.

36. Identify each of the following as (P) polar or (NP) nonpolar:
A. PBr3
B. HBr
C. Br2
D. SiBr4
(P); dipoles don’t cancel;
(P) one polar bond (dipole);
(NP) element; nonpolar bond;
(NP) symmetric; dipoles cancel