Chapter 8

1. Chapter 8 Covalent bonding

2. I. Octet Rule • What is the Octet Rule? • The octet rule states that atoms lose gain or share electrons in to acquire a full set of 8 valence electrons Create a drawing of Mg and Cl, Al and Cl

3. II. Covalent Bonds A Chemical Bond occurs when electron are shared. A molecules are formed from the overlap of orbitals and sharing of electrons Hydrogen and Hydrogen

4. Covalent bonds a. Nonmetals hold onto their valence electrons. b. They can’t give away electrons to bond. Still want noble gas configuration. c. Get it by sharing valence electrons with each other. d. By sharing both atoms get to count the electrons toward noble gas configuration.

5. Its all in the distance • Too far no bond • Too close electrons repel • Just right and a molecule is born A molecules are formed from the overlap of orbitals and sharing of electrons

6. Covalent clip

7. III. Molecule • A. a covalently bonded compound. • 1. Tend to occur between non metals that are close together on the periodic table. • a. diatomic molecules – occur naturally in nature a. this is a more stable arrangement. H H F F Br Br Cl Cl N N

9. I. Single Covalent Bond A. A sharing of two valence electrons. 1.Only nonmetals and Hydrogen. 2.Different from an ionic bond because they actually form molecules. 3. Two specific atoms are joined.

10. + + How does H2 form? • The nuclei repel

11. When Atoms Combine to make Molecules Fig 8-1 Atoms contain both positive and negative charges. When they come Together they arrange themselves so that the attractive forges of opposite Charges is greater than the repulsive forces of like charges

12. + + How does H2 form? • The nuclei repel • But they are attracted to electrons • They share the electrons

13. How to show how they formed • It’s like a jigsaw puzzle. • I have to tell you what the final formula is. • You put the pieces together to end up with the right formula. • For example- show how water is formed with covalent bonds.

14. 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 happy

15. O Water • Put the pieces together • The first hydrogen is happy • The oxygen still wants one more H

16. O Water • The second hydrogen attaches • Every atom has full energy levels H H

17. use acetate sheets to work on page 244 1-5 to create lewis structures • Use a square of acetate to show each atom (use vis a vis pens only) • Show the overlap of orbitals • Draw the outcome in your notebook-use structural formula (line to represent pair) • Circle the shared pairs

18. Lewis structure • 1. PH3 • 2. H2S • 3. HCl • 4. CCl4 • 5. SiH4

19. Lewis structure • Use molecular model kit to build • 1. PH3 • 2. H2S • 3. HCl • 4. CCl4

20. Covalent Bond Formation • Covalent bond forms by overlap of orbitals. • Two types of bonds • Sigma bond: all single bonds are sigma bonds • Pi bond: in multiple bonds: the first one is sigma, all other bonds are pi. There are • Single bonds • Multiple bonds (double and triple only)

21. Sigma bonds from overlap of orbitals along the axis connecting the nuclei between the atoms Pi bond (p bond): perpendicular overlap of p-orbitals above and below the axis connecting the atoms Two types of Bonds

22. Sigma bond: s-s Orbital Overlap

23. Pg 247- # 12 a-e

24. III. Multiple Bonds A. Sometimes atoms share more than one pair of valence electrons. B. A double bond is when atoms share two pair (4) of electrons. C. A triple bond is when atoms share three pair (6) of electrons.

25. O Carbon dioxide • CO2- Carbon is central atom( I have to tell you) • Carbon has 4 valence electrons • Wants 4 more • Oxygen has 6 valence electrons • Wants 2 more C

26. O Carbon dioxide • Attaching 1 oxygen leaves the oxygen 1 short and the carbon 3 short C

27. O O Carbon dioxide • Attaching the second oxygen leaves both oxygen 1 short and the carbon 2 short C

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

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

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

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

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

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

34. Carbon dioxide • The only solution is to share more • Requires two double bonds • Each atom gets to count all the atoms in the bond O C O

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

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

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

38. How to draw them • Add up all the valence electrons. • Count up the total number of electrons to make all atoms complete octet rule. • Subtract. • Divide by 2 • Tells you how many bonds - draw them. • Fill in the rest of the valence electrons to fill atoms up.

39. Examples • NH3 • N - has 5 valence electrons wants 8 • H - has 1 valence electrons wants 2 • NH3 has 5+3(1) = 8 • NH3 wants 8+3(2) = 14 • (14-8)/2= 3 bonds • 4 atoms with 3 bonds N H

40. Examples • Draw in the bonds • All 8 electrons are accounted for • Everything is full H H N H

41. Examples • HCN C is central atom • N - has 5 valence electrons wants 8 • C - has 4 valence electrons wants 8 • H - has 1 valence electrons wants 2 • HCNhas 5+4+1 = 10 • HCNwants 8+8+2 = 18 • (18-10)/2= 4 bonds • 3 atoms with 4 bonds -will require multiple bonds - not to H

42. HCN • Put in single bonds • Need 2 more bonds • Must go between C and N H C N

43. HCN • Put in single bonds • Need 2 more bonds • Must go between C and N • Uses 8 electrons - 2 more to add H C N

44. 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 N to fill octet H C N

45. 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 =

46. Structural Examples • C has 8 electrons because each line is 2 electrons • Ditto for N • Ditto for C here • Ditto for O H C N H C O H

47. Build the molecules using the molecular model kit. • HCN • H2O • NH3 • CH4 • C2H2 • PH3 • H2S • http://www.youtube.com/watch?v=NYFE5uslaNo

48. http://www.youtube.com/watch?v=NYFE5uslaNo

49. IV. Bond strength A. bond strength is the energy needed to break a covalent bond • Bond length and atom size help determine bond strength a. The shorter the bond length The greater the bond strength i. single bond – longest length ii. Double bond – medium length iii triple bond – shortest length WHICH HAS THE GREATEST BOND STRENGTH?

50. B. Energy is needed to create and break a covalent bond. 1.Energy is released when a covalent bond forms 2. Bond dissociation energy- is needed to break a bond a. always a positive number i. It takes 159KJ/mol to break F2 Would it take more or less to break N2 - why?