1. Part 1:Lewis Dot Diagrams and Structures
Lesson 4 – Lewis Diagrams and Molecular Geometry
Part 1:Lewis Dot Diagrams and Structures

2. Review of Chemical Bonds
There are 3 forms of bonding:
_________—complete transfer of 1 or more electrons from one atom to another (one loses, the other gains) forming oppositely charged ions that attract one another
_________—some valence electrons shared between atoms
_________ – holds atoms of a metal together

3. The type of bond can usually be calculated by finding the difference in electronegativity of the two atoms that are going together.

4. Electronegativity Difference
If the difference in electronegativities is between:
≥ 2.0: Ionic
0.>0.4 to < 2.0: Polar Covalent
0.0 to 0.4: Non-Polar Covalent
Example: NaCl
Na = 0.8, Cl = 3.0
Difference is 2.2, so
this is an ionic bond!

5. Review of Valence Electrons
Remember from the electron arrangement that valence electrons are the electrons in the OUTERMOST energy level.
B is 1s2 2s2 2p1; so the outer energy level is 2, and there are 2+1 = 3 electrons in level 2. These are the valence electrons!
Br is [Ar] 4s2 3d10 4p5 How many valence electrons are present?

6. Lewis Dot Diagrams
A way of keeping track of valence electrons in ionic compounds.
How to write them?
Write the symbol.
Put one dot for each valence electron
Don’t pair up until they have to (Hund’s rule) X

7. The Lewis Dot diagram for Nitrogen
Nitrogen has 5 valence electrons.
First we write the symbol. N
Then add 1 electron at a time to each side.
Until they are forced to pair up.

8. Ca Lewis Dots For Cations
Metals will have few valence electrons (usually 3 or less) Ca

9. Ca Lewis Dots For Cations Metals will have few valence electrons
These will come off Ca

10. Ca2+ Lewis Dots For Cations Pseudo-noble gas configuration
Metals will have few valence electrons
These will come off
Forming positive ions
Ca2+
Pseudo-noble gas configuration

11. P P3- Lewis Dots For Anions
Nonmetals will have many valence electrons (usually 5 or more)
They will gain electrons to fill outer shell. P
P3-

12. Ionic Bonding
Anions and cations are held together by opposite charges.
The bond is formed through the transfer of electrons.
Electrons are transferred to achieve noble gas configuration (octet rule).

13. Lewis Dot Diagrams Ionic BondingNa Cl

14. Lewis Dot Diagrams Ionic Bonding
Na+
Cl-

15. Lewis Dot Diagrams Ionic Bonding
All the electrons must be accounted for! Ca P

16. Lewis Dot Diagrams-Ionic BondingCa P

17. Lewis Dot Diagrams Ionic Bonding
Ca2+ P

18. Lewis Dot Diagrams Ionic Bonding
Ca2+ P Ca

19. Lewis Dot Diagrams Ionic Bonding
Ca2+
P 3- Ca

20. Lewis Dot Diagrams Ionic Bonding
Ca2+
P 3- Ca P

21. Lewis Dot Diagrams Ionic Bonding
Ca2+
P 3-
Ca2+ P

22. Lewis Dot Diagrams Ionic BondingCa
Ca2+
P 3-
Ca2+ P

23. Lewis Dot Diagram Ionic BondingCa
Ca2+
P 3-
Ca2+ P

24. Ionic Bonding
Ca2+
Ca2+
P 3-
Ca2+
P 3-

25. Lewis Dot Diagram Ionic Bonding
= Ca3P2
Formula Unit

26. Lewis Structures –Covalent Bonding

27. Covalent bonds Nonmetals hold on to their valence electrons.
Still want noble gas configuration.
By sharing, both atoms get to count the electrons toward a noble gas configuration.

28. Covalent bonding
Fluorine has seven valence electrons F

29. F F Covalent bonding Fluorine has seven valence electrons
A second atom also has seven F F

30. F F Covalent bonding Fluorine has seven valence electrons
A second atom also has seven
By sharing electrons… F F

31. F F Covalent bonding Fluorine has seven valence electrons
A second atom also has seven
By sharing electrons… F F

32. F F Covalent bonding Fluorine has seven valence electrons
A second atom also has seven
By sharing electrons… F F

33. F F Covalent bonding Fluorine has seven valence electrons
A second atom also has seven
By sharing electrons… F F

34. F F Covalent bonding Fluorine has seven valence electrons
A second atom also has seven
By sharing electrons… F F

35. F F Covalent bonding Fluorine has seven valence electrons
A second atom also has seven
By sharing electrons…
…both end with full orbitals F F

36. F F Covalent bonding Fluorine has seven valence electrons
A second atom also has seven
By sharing electrons…
…both end with full orbitals F F
8 Valence electrons

37. Drawing Lewis Structures
Find total # of valence e-.
Arrange atoms - singular atom is usually in the middle.
Form bonds between atoms (2 e-).
Distribute remaining e- to give each atom an octet
If there aren’t enough e- to go around, form double or triple bonds.

38. H O Water Each hydrogen has 1 valence Electron (Total of 2e)
Each hydrogen wants 1 more
The oxygen has 6 valence electrons
The oxygen wants 2 more
They share to make each other happy H O

39. H O Water Put the pieces together (8 e to distribute).
The first hydrogen is happy
The oxygen still wants one more H O

40. H O H Water The second hydrogen attaches
Every atom has full energy levels
Remember to check count. H O H

41. Drawing Lewis Structures
CF4
1 C × 4e- = 4e-
4 F × 7e- = 28e-
32e- F
F C F
- 8e-
24e-

42. Drawing Lewis Structures
BeCl2
1 Be × 2e- = 2e-
2 Cl × 7e- = 14e-
16e-
Cl Be Cl
- 4e-
12e-

43. Multiple Bonds
Sometimes atoms share more than one pair of valence electrons.
A double bond is when atoms share two pairs (4 total) of electrons
A triple bond is when atoms share three pairs (6 total) of electrons
Know which elements are diatomic (Oxygen?)

44. C O Carbon dioxide CO2 - Carbon is central atom ( more metallic )
Carbon has 4 valence electrons
Oxygen has 6 valence electrons (total of 12e)
16e must be distributed. C O

45. Carbon dioxide
Attaching 1 oxygen leaves the oxygen 1 short, and the carbon 3 short C O

46. Carbon dioxide
Attaching the second oxygen leaves both oxygen 1 short and the carbon 2 short
IF the central atom is not surrounded by 4 electron pairs, it does not have an octet. You must convert one or more of the lone pairs on the terminal atoms to a double or triple bonds. O C O

47. Carbon dioxide
The only solution is to share more O C O

48. Carbon dioxide
The only solution is to share more O C O

49. Carbon dioxide
The only solution is to share more O C O

50. Carbon dioxide
The only solution is to share more O C O

51. Carbon dioxide
The only solution is to share more O C O

52. Carbon dioxide
The only solution is to share more O C O

53. O C O Carbon dioxide The only solution is to share more
Requires two double bonds
Each atom can count all the electrons in the bond O C O

54. O C O Carbon dioxide 8 valence electrons
The only solution is to share more
Requires two double bonds
Each atom can count all the electrons in the bond
Count e’s
8 valence electrons O C O

55. O C O Carbon dioxide The only solution is to share more
Requires two double bonds
Each atom can count all the electrons in the bond
8 valence electrons O C O