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

2. Learning Goals By the end of this lesson you will be able to:
Be able to define covalent bond
Be able to react 2 non-metals to create covalent bond
Use the octet rule to for stable covalent molecules.

3. Covalent Bonds
Bond formed by a shared pair of electrons between 2 non-metal atoms
Gives atom an octet of electrons
Shared pair of electrons – bonding pair
Other electrons not involved in bonding – nonbonding pairs (a.k.a. lone pairs)
Covalent bonds can be either
1) non-polar covalent
2) polar covalent (to be discussed later)

9. Covalent Bonds example
Chlorine does not occur in nature as an isolated atom Cl Cl Cl
Bonding Pair Cl Cl
Lone Pair
Chlorine atoms share electrons to get full shell

10. Cl Cl Review of Octet rule 8 7 8 7 1 6 1 6 2 5 5 2 3 4 3 4
Octet rule - most covalently bonded atoms represented in a Lewis structure have 8 electrons in their valence shells. 8 7 8 7 Cl Cl 1 6 1 6 2 5 5 2 3 4 3 4

12. H H H2 F2 F I2 Br2 I Cl2 Br Cl Diatomic Molecules Fluorine Bromine
Hydrogen Halogens H H H2 F F2 Br
Br2
Fluorine
Bromine Cl I I2
Cl2
Chlorine
Iodine

13. Dash Notation for Covalent bonds
Since the dots for electrons get crowded, dashes can be used to represent a covalent bond H H H2 H H

14. 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

15. Multiple Covalent bonds
Only 7 electrons does
Not meet Octet Rule!
Need to share
Another pair of
electrons O O
Sharing One Pair of electrons
One Covalent Bond O O O O
A Double Bond can be represented by a double line
Sharing Two Pairs of electrons
Two Covalent Bonds
A Double Bond

16. Multiple Covalent bonds
Nitrogen N N
Sharing Three Pairs of electrons
Three Covalent Bonds
A Triple Bond N N
A Triple Bond can be represented by a Triple line

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

18. 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

19. Naming Covalent Compounds
Common Names
Water H2O
Ammonia NH3
Methane CH4 O H N H C H

20. 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

21. 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

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

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

24. 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

25. 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-

26. 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

27. Practice
OF2

28. Layout:
O-F-F

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

30. Layout:
O=F-F

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

32. Layout:
F-O-F

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

34. Practice
Place bonding electrons for connected atoms

35. Practice
Place bonding electrons for connected atoms

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

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

38. Practice
Similarly, add lone pairs for fluorines:

39. 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

40. Now You Do One:
Now You Do One:
CH2CL2

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

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

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

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

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

46. Layout: C H Cl
Correct!

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

49. And Another
OCS

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

51. Layout?
O C S or
C S O
S O C ??

52. 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

53. Great!