1. Polarity in Covalent Bonds
Bonding Movie

2. Polar Bond Polar means poles uneven distribution of electrons
Polar bond: one end of bond has more electrons than other end

3. Nonpolar Bond Nonpolar = No poles even distribution of electrons
electron cloud same on one end of bond as other end

4. H2 is symmetric: Both ends the same; electron cloud football-shaped
HCl is asymmetric: electron cloud
lopsided; Cl side more electrons than H side

5. Which bond(s) are polar? Which are nonpolar?
Polar: LiH & HF Nonpolar: H2
Red: e- rich
Blue: e- poor

6. How can predict if BOND is polar or not?
Compare electronegativity values of two atoms in bond

7. Electronegativity
Ability of atom to attract electrons in bond
Found in Table S!

8. Electronegativities of the Elements

9. Bond Polarity
more electronegative atom pulls bonding e- more strongly & gets more than fair share of electron cloud
leads to separation of charge
electron-rich side is partially negative (-)
electron-poor side is partially positive (+)

10. Delta notation

11. BOND Polarity A B EA - EB  
Depends on electronegativity difference between two atoms in bond
A B
EA - EB
 
- care only about size of difference, not sign
- bigger the difference, the more polar the bond

12. Calculate electronegativity difference for each of these bonds
2.1 – 4
1.9
LiH : H2 : HF:
2.1 – 1.0
1.1
2.1 – 2.1

13. Bond Polarity
What can say about polarity of bond where atom A is same as atom B?
If both atoms are same element:
electronegativity difference = 0
therefore will be non-polar

14. Electronegativity Difference
ionic
> 1.7
polar covalent
>0.5 to 1.7
nonpolar covalent
0.0 to 0.5
Type of
Bond
Difference in Electronegativities

15. Electronegativity & Bond Type

16. Review Which of following bonds is most polar? A) O2 B) HCl
C) NH in NH3
D) HBr
3.4 – 3.4 = 0
2.1 – 3.2 = -1.1 = 1.1
3.0 – 2.1 = 0.9
3.0 – 2.1 = 0.9
Answer =(B) HCl

17. Review Which substance contains bond with greatest ionic character?
A) KCl
B) HCl
C) Cl2
D) CCl4
0.8 – 3.2 = -2.4 = 2.4
2.1 – 3.2 = -1.1 = 1.1
3.2 – 3.2 = 0
2.6 – 3.2 = -0.6 = 0.6
Answer = (A) KCl

18. Summary Nonpolar covalent bonds form: Polar covalent bonds form:
between atoms having equal or close electronegativity values:
Polar covalent bonds form:
between atoms with electronegativity difference >0.5 to 1.7

19. Predict the Polarity Nonpolar N2 HF HCl Polar O2 Cl2 Polar HI HBr

20. MOLECULE Polarity Diatomic molecules: molecular polarity is same as
bond polarity

21. MOLECULE Polarity (3+ elements)
Depends on 2 factors
1. Type bonds in molecule
2. Arrangement of bonds or shape of molecule
Think SYMMETRY!!

22. For larger molecules:
look at kind & arrangement of bonds to determine overall polarity of molecule

23. Polarity of Molecules
molecule may contain polar bonds, but not be polar!
depends on geometry of molecule
If molecule is symmetric:
“pull” of one polar bond is offset by “pull” of another polar bond
tug-of-war that no one can win!

24. Symmetric Molecules
Contain at least two mirror planes of symmetry

25. Symmetric vs. Asymmetric
CO2 is nonpolar: electron cloud is symmetric
H2O is polar: electron cloud lop-sided (asymmetrical)

26. Polarity of CO2?
Draw arrow along each bond pointing to more electronegative atom
If arrows cancel out, molecule is NONPOLAR

27. Polarity of H2O?
green arrows do NOT cancel out
- water is polar!

28. structural formula can be used to predict Molecular Polarity!H
H  C  H  

29. Symmetry of Larger Molecules
CF4 is symmetric so is nonpolar

30. Ethane = C2H6
Ethene = C2H4
Ethyne = C2H2
These molecules are symmetric - electron cloud is same on both ends: they are nonpolar