1. Sharing of Electron Pairs Non-metal with Non-metal Atoms
Covalent Bonding
Sharing of Electron Pairs
Non-metal with Non-metal Atoms

2. Covalent Bonding Like ionic bonds, covalent bonds are +/- attractions.
Closed-shell considerations often explain the patterns of bonding, i.e., the formulas -- just as for ionic systems

3. H2 H e- H e-
Neutral atoms
Push ‘em together...

4. H2 e- H H : H The pair of shared electrons Equivalent to:
Positive nuclei
Negative shared electrons

5. H C 6C
2e-
4e- 1H
1e-
Equivalent to: C H·
Outer e- only shown

6. H C H· C H· H· H·
Outer e- only shown

7. :H H + C : : H H: C H 2 e- at each H 8 e- at carbon
Positive nuclei H
2 e- at each H : H: :H C :
Negative electrons H
8 e- at carbon
all atoms closed shell
Outer e- only shown

8. H N N : H· H· H·
Outer e- only shown

9. :H H + N : : H: N H 2 e- at each H 8 e- at nitrogen
all atoms closed shell
Outer e- only shown

10. H O
O : : H· H·
Outer e- only shown

11. : H + O : : H: O H 2 e- at each H 8 e- at oxygen
all atoms closed shell
Outer e- only shown

12. H F
: F : : H·
Outer e- only shown

13. : : H + F : : F H 8 e- at fluorine all atoms closed shell 2 e- at H
Outer e- only shown

14. Patterns for Major Elements
CH4 C = 4 bonds; all electrons shared
NH3 N = 3 bonds; one lone pair
H2O O = 2 bonds; two lone pairs
HF F = 1 bond; three lone pairs

15. 4 Bonds
All e- shared
Carbon, group IV
3 Bonds
1 Lone Pair
Nitrogen, Group V
2 Bonds
2 Lone Pairs
Oxygen, Group VI
1 Bond
3 Lone pairs
Fluorine, Group VII

16. Other Compounds Have Same Pattern
C = 4 bonds; Cl (like F) = 1 bond
P (like N = 3 bonds; Br (like F) = 1 bond

17. More Similarities: S (like Oxygen) = 2 bonds, 2 lone pairs
C = 4 bonds; O = 2 bonds, 2 lone pairs

18. Multiple Bonds Atoms may share more than one pair of electrons
a DOUBLE BOND forms when atoms share two pairs of electrons (4 e-)
a TRIPLE BOND forms when atoms share three pairs of electrons (6 e-)
Total number of bonds per atom unchanged

19. Multiple Bonds C2H4 Valence e- = 12 H2CO Valence e- = 12
4 Bonds, each carbon
H2CO Valence e- = 12
Two bonds at oxygen

20. Multiple Bonds Total valence e- = 16 (Oxygen = 6 e-, each;
Carbon = 4 e-. Four bonds/C; 2 bonds oxygen
Total valence e- = 10 (H=1, C=4, N=5)
Bonds: C=4, N=3, H=1
Total valence e- = 18 (O=6, Cl = 7, P = 5)
Bonds: Cl=1, P=3, O=2

21. Predicting Dot Diagrams
How Do We Proceed?
Determine total number of valence electrons
Based on usual bond nos., identify reasonable layout for atoms
Place bonding electrons between atoms to make usual no. of bonds
Place remaining electrons as lone pairs around atoms still lacking an octet

22. Total number of Valence e-
Sum of group numbers for atoms of representative elements
Eg., C = 4e- N = 5e- O = 6e- H = 1e-
CCl4 = 4e- + (4 x 7e-) = 32e-
SO2 = 6e- + (2 x 6e-) = 18e-
N2H4 = (2 x 5e-) + (4 x 1e-) = 14e-
C3H8 = (3 x 4e-) + (8 x 1e-) = 20e-

23. Based on Covalence (Usual Bonds) Nos.
Reasonable Layouts
Based on Covalence (Usual Bonds) Nos.
H2S -- 1 Bond each H; 2 Bonds for S
H-H=S Incorrect - One H has 3 bonds
H-S-H Correct - All atoms with usual bond numbers (H=1; S=2)
PCl3
Cl=P-Cl-Cl Incorrect - One Cl has two bonds
Cl-P-Cl Correct -- (Cl=1; P=3) | Cl

24. Practice
OF2

25. Layout:
O-F-F

26. Layout:
O-F-F Incorrect -- One F with two bonds; O only one bond

27. Layout:
O=F-F

28. Layout:
O=F-F Incorrect -- One F with three bonds; (O does have two bonds)

29. Layout:
F-O-F

30. Layout:
F-O-F Correct -- F = 1 bond, each; O = 2 bonds)

31. Practice
Place bonding electrons for connected atoms

32. Practice
Place bonding electrons for connected atoms

33. Practice
Add lone pairs for atoms needing “octet”

34. Practice
Add lone pairs for atoms needing “octet”

35. Practice
Similarly, add lone pairs for fluorines:

36. Practice Check Results! Correct total e- (O = 6; F = 7, ea) = 20e-
Usual bond nos. (O=2; F=1, ea)
Closed shell (octets) O=8; F=8 each

37. Now You Do One:
CH2Cl2

38. Total e- C = 4 e- H = 1e-, each, 2 total Cl = 7e-, each = 14 more
Grand total = 20e-

39. Layout:
H-H-C-Cl-Cl

40. Layout:
H-H-C-Cl-Cl Incorrect

41. Layout:
H-C-Cl-Cl-H Incorrect

42. Layout:
H-H-Cl=C=Cl Incorrect

43. Layout: C H Cl
Correct!

45. Check Results:
Total e-
Usual no. Bonds
Closed Shells

46. And Another
OCS

47. C = 4e- O = 6e- S = 6e- Total = 16e-
Number e-
C = 4e-
O = 6e-
S = 6e-
Total = 16e-

48. Layout?
O C S or
C S O
S O C ??

49. 2 Bonds for O; 4 Bonds for C; 2 Bonds for S
Layout
O=C=S
2 Bonds for O; 4 Bonds for C; 2 Bonds for S

50. Great!