1 / 51

Chapter 8 “Covalent Bonding”

Chapter 8 “Covalent Bonding”. Ball-and-stick model. Section 8.1 Molecular Compounds. OBJECTIVES: Distinguish between the melting points and boiling points of molecular compounds and ionic compounds. Section 8.1 Molecular Compounds. OBJECTIVES:

toan
Download Presentation

Chapter 8 “Covalent Bonding”

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript


  1. Chapter 8“Covalent Bonding” Ball-and-stick model

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

  5. Covalent Bonds • The word covalent is a combination of the prefix co- (from Latin com, meaning “with” or “together”), and the verb valere, meaning “to be strong”. • Two electrons shared together have the strength to hold two atoms together in a bond.

  6. 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)

  7. + + + + How does H2 form? • The nuclei repel each other, since they both have a positive charge (like charges repel). (diatomic hydrogen molecule)

  8. + + 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!

  9. 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.

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

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

  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…

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

  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

  19. 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 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

  21. Molecular Compounds • Thus, 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

  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: • Describehow 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: • Describe how oxygen atoms are bonded in ozone.

  28. 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

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

  30. 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

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

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

  33. 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

  34. 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

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

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

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

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

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

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

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

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

  43. 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

  44. 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

  45. 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

  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. 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

  48. 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

  49. Resonance in Ozone Note the different location of the double bond Neitherstructure is correct, it is actually a hybrid of the two. To show it, draw all varieties possible, and join them with a double-headed arrow.

More Related