Chapter 8 “Covalent Bonding”

1. Chapter 8“Covalent Bonding”

2. Section 8.1Molecular Compounds • OBJECTIVES: • Distinguish between the melting points and boiling points of molecular compounds and ionic compounds.

3. Section 8.1Molecular Compounds • OBJECTIVES: • Describe the information provided by a molecular formula.

4. Bonds • Forces that hold groups of atoms together and make them function as a unit: • Ionic bonds – transfer of electrons (gained or lost) • Covalent bonds – sharing of electrons. The resulting particle is called a “molecule”.

5. 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”

6. + + How does H2 form? • The nuclei repel each other, since they both have a positive charge, and like charges repel.

7. + + How does H2 form? • But, the nuclei are attracted to the electrons • They share the electrons, and this is called a “covalent bond”, and involves only NONMETALS!

8. Covalent bonds • Nonmetals hold on to their valence electrons. • They can’t give away electrons to bond. • 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.

9. F Covalent bonding • Fluorine has seven valence electrons

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

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

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

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

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

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

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

17. 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. 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

20. Molecular Compounds • Compounds that are bonded covalently (like water and carbon dioxide) are called molecular compounds • Molecular compounds tend to have relatively lower melting and boiling points than ionic compounds.

21. Molecular Compounds • Thus, molecular compounds tend to be gases or liquids at room temperature • Ionic compounds were solids • A molecular compound consists of a molecular formula: • Shows how many atoms of each element a molecule contains

22. Molecular Compounds • The formula for water is written as H2O • The subscript 2 behind hydrogen means there are 2 atoms of hydrogen; if there is only one atom, the subscript 1 is omitted • Molecular formulas do not tell any information about the structure (the arrangement of the various atoms).

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

24. Section 8.2The Nature of Covalent Bonding • OBJECTIVES: • Describe how electrons are shared to form covalent bonds, and identify exceptions to the octet rule.

25. Section 8.2The Nature of Covalent Bonding • OBJECTIVES: • Demonstrate how electron dot structures represent shared electrons.

26. Section 8.2The Nature of Covalent Bonding • OBJECTIVES: • Describe how atoms form double or triple covalent bonds.

27. Section 8.2The Nature of Covalent Bonding • OBJECTIVES: • Distinguish between a covalent bond and a coordinate covalent bond, and describe how the strength of a covalent bond is related to its bond dissociation energy.

28. Section 8.2The Nature of Covalent Bonding • OBJECTIVES: • Describe how oxygen atoms are bonded in ozone.

29. A Single Covalent Bond is... • A sharing of two valence electrons. • Only nonmetals and hydrogen. • Different from an ionic bond because they actually form molecules. • Two specific atoms are joined. • In an ionic solid, you can’t tell which atom the electrons moved from or to

30. Sodium Chloride Crystal Lattice • Ionic compounds organize in a characteristic crystal lattice of alternating positive and negative ions.

31. How to show the formation… • It’s like a jigsaw puzzle. • You put the pieces together to end up with the right formula. • Carbon is a special example - can it really share 4 electrons: 1s22s22p2? • Yes, due to electron promotion! • Another example: lets show how water is formed with covalent bonds, by using an electron dot diagram

32. 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

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

34. O Water • A second hydrogen attaches • Every atom has full energy levels Note the two “unshared” pairs of electrons H H

35. Multiple Bonds • Sometimes atoms share more thanone 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) • Table 8.1, p.222 - Know these 7 elements as diatomic: Br2 I2 N2 Cl2 H2 O2 F2 What’s the deal with the oxygen dot diagram?

36. O 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

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

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

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

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

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

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

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

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

45. 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

46. 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

47. 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

48. 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

49. How to draw them? • Use the handout guidelines: • Add up all the valence electrons. • Count up the total number of electrons to make all atoms happy. • Subtract; then Divide by 2 • Tells you how many bonds to draw • Fill in the rest of the valence electrons to fill atoms up.

50. 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