1. Unit 7 Chemical Bonds
Ball-and-stick model
2. Covalent Bonding

2. Bonds are… Ionic bonds – transfer of electrons
Forces that hold atoms together and make them function as a unit. Two types:
Ionic bonds – transfer of electrons
Covalent bonds – sharing of electrons.

3. Covalent Bonds
Two electrons shared together have the strength to hold two atoms together in a bond.

4. Molecules Many elements found in nature are in the form of molecules:
a neutral group of atoms joined together by covalent bonds.
For example, air contains oxygen molecules, consisting of two oxygen atoms joined covalently
Called a “diatomic molecule” (O2)

5. How does H2 form?
They share the electrons, and this is called a “covalent bond”, and involves only NONMETALS! + +

6. Covalent bonds Nonmetals hold on to their valence electrons.
They can’t give away electrons to bond.
But still want noble gas configuration.
Get it by sharing valence electrons with each other = covalent bonding
By sharing, both atoms get to count the electrons toward a noble gas configuration.

7. # electrons 1 8 2 3 4 5 6 7

8. Covalent bonding
Fluorine has seven valence electrons (but would like to have 8) F

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

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

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

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

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

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

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

16. 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

17. 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

18. Molecular Compounds
Compounds that are bonded covalently (like in water, or carbon dioxide) are called molecular compounds
Molecular compounds tend to have relatively lower melting and boiling points than ionic compounds – this is not as strong a bond as ionic

19. Molecular Compounds Tend to be gases or liquids at room temperature
Ionic compounds were solids
A molecular compound has a molecular formula:
Shows how many atoms of each element a molecule contains

20. Molecular Compounds The formula for water is written as H2O
# of atoms Oxygen ( O )
# of atoms Hydrogen ( H )

21. - Page 215
These are some of the different ways to represent ammonia:
3. The ball and stick model is the BEST, because it shows a 3-dimensional arrangement.
1. The molecular formula shows how many atoms of each element are present
2. The structural formula ALSO shows the arrangement of these atoms!

23. Ionic and covalent bonding animation

24. H O Water Each hydrogen has 1 valence electron
- Each hydrogen wants 1 more
The oxygen has 6 valence electrons
- The oxygen wants 2 more
They share to make each other complete H O

25. H O Water Put the pieces together The first hydrogen is happy
The oxygen still needs one more H O

26. H O H Water So, a second hydrogen attaches
Every atom has full energy levels
Note the two “unshared” pairs of electrons H O H

27. Multiple Bonds
Sometimes atoms share more than one pair of valence electrons.
A double bond is when atoms share two pairs of electrons (4 total)
A triple bond is when atoms share three pairs of electrons (6 total)

28. Dot diagram for Carbon dioxide
CO2 - Carbon is central atom ( more metallic )
Carbon has 4 valence electrons
Wants 4 more
Oxygen has 6 valence electrons
Wants 2 more C O

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

30. Carbon dioxide
Attaching the second oxygen leaves both of the oxygen 1 short, and the carbon 2 short O C O

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

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

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

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

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

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

37. 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

38. 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

39. 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

40. 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

41. N H Example NH3, which is ammonia
N – central atom; has 5 valence electrons, wants 8
H - has 1 (x3) valence electrons, wants 2 (x3)
NH3 has 5+3 = 8
NH3 wants 8+6 = 14
(14-8)/2= 3 bonds
4 atoms with 3 bonds N H

42. H H N H Examples Draw in the bonds; start with singles
All 8 electrons are accounted for
Everything is full – done with this one. H H N H

43. Example: HCN HCN: C is central atom
N - has 5 valence electrons, wants 8
C - has 4 valence electrons, wants 8
H - has 1 valence electron, wants 2
HCN has = 10
HCN wants = 18
(18-10)/2= 4 bonds
3 atoms with 4 bonds – this will require multiple bonds - not to H however

44. H C N HCN Put single bond between each atom Need to add 2 more bonds
Must go between C and N (Hydrogen is full) H C N

45. H C N HCN Put in single bonds Needs 2 more bonds
Must go between C and N, not the H
Uses 8 electrons – need 2 more to equal the 10 it has H C N

46. H C N HCN Put in single bonds Need 2 more bonds
Must go between C and N
Uses 8 electrons - 2 more to add
Must go on the N to fill its octet H C N

47. Another way of indicating bonds
Often use a line to indicate a bond
Called a structural formula
Each line is 2 valence electrons H O H H O H =

48. Other Structural Examples
H C N H
C O H

50. HOLT BOOK ACTIVITIES Definition: Covalent Bond (p 186 )
Figure 5 ( p 186 )
Chapter 6 Review: 8,9 ( p 210 )
Understanding Concepts 1,2 ( p 212 )