Chemical bonding chapter 6


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Chapter 6: Chemical Bonding, Modern Chemistry. This is a working presentation of the notes for this chapter. Meaning that we may or may not cover all of the material here.

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Chemical bonding chapter 6

  1. 1. Chapter 6 – ModernCHEMICAL BONDING Chemistry S.Martinez
  2. 2. CHEMICAL BONDING In a chemical bond between atoms, their valence electrons are redistributed in ways that make the atoms more stable. The way that atoms are redistributed determines the type of bonding.11/19/2010 S.Martinez 2
  3. 3. T YPES OF CHEMICAL BONDING1. Ionic Bonding – chemical bonding that results from the electrical attraction between large numbers of cations (+, metals) and anions ( -, nonmetals).2. Covalent Bonding – results from the sharing of electron pairs between two atoms.11/19/2010 S.Martinez 3
  4. 4. 11/19/2010 S.Martinez 4
  5. 5. IONIC OR COVALENT??? Electronegativity is a measure of an atom’s ability to attract electrons. By calculating the dif ference in the bonded elements’ electronegativity, the type of bond can be determined(ionic or covalent)….generally bonds are not 100% ionic or covalent but a mixture.11/19/2010 S.Martinez 5
  6. 6. COVALENT OR IONIC???Type of Bond Difference in Percentage electronegati of ionic vities characterNonpolar- 0 to 0.3 0 to 5%covalentbondsPolar- 0.3 to 1.7 5 to 50%covalentbondsIonic bonds 1.7 to 3.3 50 to 100% 11/19/2010 S.Martinez 6
  7. 7. 11/19/2010 S.Martinez 7
  8. 8. T YPES OF COVALENT BONDING1. Nonpolar Covalent – a covalent bond in which the bonding electrons are shared equally by the bonded atoms, resulting in a balanced distribution of electrical charge.2. Polar Covalent – is a covalent bond in which the bonded atoms have an unequal attraction for the shared electrons…..uneven distribution of charge.11/19/2010 S.Martinez 8
  9. 9.  Example: When Hydrogen and Chlorine combine the dif ference in their electronegativites is 3.0 – 2.1 = 0.9, indicating a polar covalent bond. The electrons in this bond are closer to the more electronegative chlorine atom that to the hydrogen atom. The chlorine end of the bond has a partial negative charge, indicated by the symbol δ - . The hydrogen end has a partial positive charge, δ + .11/19/2010 S.Martinez 9
  10. 10. PRACTICE PROBLEMS See periodic table on page 151 for values of electronegativity. Classify the following bonds as either ionic, nonpolar covalent, or polar covalent.Chlorine & CalciumChlorine & OxygenChlorine & Bromine11/19/2010 S.Martinez 10
  11. 11. Bonding Between Electronegativity Bond type More-negativeChlorine and…. difference atomCalcium 3.0 – 1.0 = 2.0 Ionic ChlorineOxygen 3.5 -3.0 = 0.5 Polar-covalent OxygenBromine 3.0 – 2.8 = 0.2 Nonpolar-covalent Chlorine11/19/2010 S.Martinez 11
  12. 12. CHAPTER 6 SECTION 1 Page 163, 1 – 4 Answer the questions in your composition book. Do not write the questions unless you feel that it is necessary.11/19/2010 S.Martinez 12
  13. 13. COVALENT BONDING Chapter 6 AND MOLECULAR Section 2 COMPOUNDS11/19/2010 S.Martinez 13
  14. 14. COVALENT BONDING & MOLECULAR COMPOUNDSMany chemical compounds are composed of molecules.Molecule – is a neutral group of atoms that are held together by covalent bonds….are capable of existing on its own. Example: Oxygen (O 2), water (H 2O), sugar (C 12H22O11)11/19/2010 S.Martinez 14
  15. 15. Molecular compound – is a chemical compound whose simplest units are molecules.Chemical formulas give the composition of a compound11/19/2010 S.Martinez 15
  16. 16. Chemical formulas also indicate the relative numbers of atoms of each kind in a chemical compound by using atomic symbols and numerical subscripts….the chem. formula of a molecular compound is called a molecular formula.11/19/2010 S.Martinez 16
  17. 17. A molecular formula show the types and numbers of atoms combined in a single molecule of a molecular compound.A diatomic molecules is a molecule containing only two atoms..ex: O 2, N 2, Cl 2, I 2, Br 2, F 2, H 211/19/2010 S.Martinez 17
  18. 18. FORMATION OF COVALENT BONDSMost atoms are at a lower potential energy when they are bonded to other atoms than they are at as independent particles….this is what makes them more stable.11/19/2010 S.Martinez 18
  19. 19. There are three different types of forces at work when atoms come together. (electron-electron, proton-proton, & electron-proton).A bond length is the distance between two bonded atoms at their minimum potential energy….this occurs at a distance when the forces of attraction = the forces of repulsion.11/19/2010 S.Martinez 19
  20. 20. 10#p/u/22/z3F7LjTvdX011/19/2010 S.Martinez 20
  21. 21.  Bond energy is the energy required to break a chemical bond and form neutral isolated atoms…this is the same amount of energy that is released as atoms change from isolated individual atoms to part of a molecule.11/19/2010 S.Martinez 21
  22. 22. Bond Bond length Bond Energy Bond Bond length Bond Energy (pm) (kJ/mol) (pm) (kj/mol) TABLE 6-1, PAGE 168H-H 74 436 C-C 154 346F-F 141 159 C-N 147 305Cl-Cl 199 243 C-O 143 358Br-Br 228 193 C-H 109 418I-I 267 151 C-Cl 177 327H-F 92 569 C-Br 194 285H-Cl 127 432 N-N 145 163H-Br 141 366 N-H 101 386H-I 161 299 O-H 96 459 11/19/2010 S.Martinez 22
  23. 23.  Bond lengths and energies vary with the type of atoms that have combined…and can vary with the same type of atoms bonding together. Bond length will decrease as bond energy or strength increases.11/19/2010 S.Martinez 23
  24. 24. THE OCTET RULEChemical compounds tend to form so that each atom, by gaining, losing, or sharing electrons, has an octet of electrons in its highest occupied energy level. (this rule applies to both ionic and covalent compounds)11/19/2010 S.Martinez 24
  25. 25. Noble-gas atoms exist independently in nature….because of their electron configurations. This stability is a result of their outermost s and p orbitals being completely filled with 8 electrons….their octet is full.11/19/2010 S.Martinez 25
  26. 26. Other main-group elements (s and p block elements) are able to obtain a stable configuration through the use of the octet rule.11/19/2010 S.Martinez 26
  27. 27. 11/19/2010 S.Martinez 27
  28. 28. EXCEPTIONS TO THE OCTET RULE Hydrogen forms bonds in which it is only surrounded by two electrons. Boron, has just three valence electrons, so it tends to form bonds in which it is only surrounded by 6 electrons. Example: BF 311/19/2010 S.Martinez 28
  29. 29. ELECTRON-DOT NOTATION Shows the electron-configuration notation in which only the valence electrons of an atom of a particular element are shown, indicated by dots placed around the element’s symbol.11/19/2010 S.Martinez 29
  30. 30. LEWIS STRUCTURES Uses dashes to show covalent bonds between atoms and uses dots to show the remaining valence or the unshared pairs of electrons.11/19/2010 S.Martinez 30
  31. 31. STRUCTURAL FORMULA Indicates the kind, number, arrangement, and bonds but not the unshared pairs of the atoms in a molecule.11/19/2010 S.Martinez 31
  32. 32. Draw the Lewis structure of iodomethane, CH 3I11/19/2010 S.Martinez 32
  33. 33. Draw the Lewis structure of ammonia, NH 311/19/2010 S.Martinez 33
  34. 34. Draw the Lewis structure for hydrogen sulfide, H 2S11/19/2010 S.Martinez 34
  35. 35. Draw the Lewis structure for methanal (aka formaldehyde), CH 2O11/19/2010 S.Martinez 35
  36. 36.  PCl5C6H10Cl2OH11/19/2010 S.Martinez 36
  37. 37. BOND LENGTHS AND ENERGIES FOR SINGLE AND MULTIPLE BONDSBond Bond Bond Bond Bond Bond Length (pm) Energy Length (pm) Energy (kJ/mol) (kJ/mol)C-C 154 346 C-O 143 358C=C 134 612 C=O 120 732C C 120 835 C O 113 107211/19/2010 S.Martinez 37
  38. 38. RESONANCE Refers to bonding in molecules that cannot be correctly represented by a single Lewis structure…..the true structure lies somewhere between the two resonance structures. A double arrow is used indicate a molecule’s resonance structure. O=O-O O-O=O11/19/2010 S.Martinez 38
  39. 39. IONIC BONDS AND Chapter 6 Section 3 COMPOUNDS11/19/2010 S.Martinez 39
  40. 40. IONIC BONDING & IONIC COMPOUNDSMost of the rocks & minerals in the Earth’s crust are composed of positive & negative ions held together by bonds.Ionic compound – composed of positive and negative ions that are combined so that the numbers of positive and negative charges are equal…generally crystals.11/19/2010 S.Martinez 40
  41. 41. Chem. Formula for an ion represents the simplest ratio of the combined ions that gives electrical neutrality.Formula unit shows the simplest collection of atoms from which an ionic compound’s formula can be established.11/19/2010 S.Martinez 41
  42. 42. Example: Rock Salt, sodium chloride, NaCl is composed of Na + & Cl -Example: calcium fluoride(the liquid form is used to melt ice on highways or in the use of oxygen sensitive applications such as the making of metal alloys), CaF 2 is composed of Ca 2+ & F-11/19/2010 S.Martinez 42
  43. 43. ELECTRON-DOT NOTATION….Can be used to demonstrate the changes that occur in ionic bonding.11/19/2010 S.Martinez 43
  44. 44. CHARACTERISTICS OF IONIC BONDING Since nature favors arrangements where PE is @ a min. ionic crystals are arranged in a crystal lattice.11/19/2010 S.Martinez 44
  45. 45. FORCES AT ACT IN THE CRYSTAL LATTICE Forces of attraction Forces of repulsion = = oppositely charged between like ions & those charged ions & between the nuclei those between & electrons of electrons of adjacent ions. adjacent ions.11/19/2010 S.Martinez 45
  46. 46. IONIC VS. MOLECULARIonic:  Molten state can conduct since ions arethe forces that hold free to move. it together are very  Some ionic compounds strong. do not dissolve in water because the attractionHigher melting & of water cannot boiling pts. Also, do overcome the attraction not vaporize @ room between ions. temp.  Solid state ions cannot move so they do not  Hard but brittle due to conduct. a large build-up of repulsion when a shift11/19/2010 S.Martinez 46 occurs.
  47. 47. Molecular – covalent bonds are also strong but not in comparison to ionic. Melt at lower temperatures or are gases @ room temp.11/19/2010 S.Martinez 47
  48. 48. POLYATOMIC IONS Is a charged group Examples: of covalently Ammonium bonded NH 4+, Nitrate NO 3- atoms…can be , Sulfate SO 42- & represented by Phosphate PO 42- Lewis structures11/19/2010 S.Martinez 48
  49. 49. Chapter 6 METALLIC BONDING Section 411/19/2010 S.Martinez 49
  50. 50. METALLIC BONDING Explains why they This is due to the are such excellent highly mobile conductors of heat & valence electrons of electricity in the the atoms that make solid state compared up a metal. to molten ionic compounds.11/19/2010 S.Martinez 50
  51. 51. This mobility is not possible in molecular or ionic compounds since they are localized or bound to individual ions that are held in place.11/19/2010 S.Martinez 51
  52. 52. The vacancy that is These electrons are observed in s-block considered to be and d-block metals delocalized, allows for an overlap meaning they do not of the vacant belong to an orbitals that in turn individual atom. allows the outer These mobile electrons to roam. electrons are referred to as a sea of electrons.11/19/2010 S.Martinez 52
  53. 53. 11/19/2010 S.Martinez 53
  54. 54. This freedom Also, since metallic accounts for  bonding is the same electrical & thermal in all directions this conductivity. accounts for why Metals can absorb metals are both wide range of light malleable frequencies (Flame (hammered into thin Test) responsible for sheets) or ductile shiny appearance. (drawn into a wire).11/19/2010 S.Martinez 54
  55. 55. METALLIC BOND STRENGTH Varies with nuclear The amt of  (heat) charge and the # of required to vaporize electrons in the the metal is a metal’s electron sea. measure of the This is reflected in strength of the the heat of bonds that hold the vaporization of a metal together. metal.11/19/2010 S.Martinez 55
  56. 56. TABLE 6-4 HEATS OF VAPORIZATION OF SOME METALS (KJ/MOL)Period Element Element ElementSecond Li – 147 Be – 297Third Na – 97 Mg – 128 Al – 294Fourth K – 77 Ca – 155 Sc – 333Fifth Rb – 76 Sr – 137 Y – 365Sixth Cs – 64 Ba – 140 La - 40211/19/2010 S.Martinez 56
  57. 57. MOLECULAR GEOMETRY VSEPR Theory (valence-shell, electron-pair repulsion) states that the repulsion between the sets of valence -level electrons surrounding an atom causes these sets to be oriented as far apart as possible.11/19/2010 S.Martinez 57
  58. 58. VESPR MODEL11/19/2010 S.Martinez 58
  59. 59. VESPR MODEL11/19/2010 S.Martinez 59
  60. 60.  Hybridization is the mixing of two or more atomic orbitals of similar energies on the same atom to produce new orbitals of equal energies. Example: Methane CH 4 1s 2 2s 2 2p 2 (see board)11/19/2010 S.Martinez 60
  61. 61. GEOMETRY OF HYBRID ORBITALS11/19/2010 S.Martinez 61
  62. 62. VESPR AND MOLECULAR GEOMETRY11/19/2010 S.Martinez 62
  63. 63. VESPR AND MOLECULAR GEOMETRY11/19/2010 S.Martinez 63
  64. 64. PREDICT THE MOLECULAR GEOMETRY FOR THE FOLLOWING: HI CBr 4 AlBr 3 CH 2 Cl 2 NH 3 H 2O PCl 5 SF 611/19/2010 S.Martinez 64
  65. 65.  Intermolecular Forces – are the forces of attraction between molecules… The stronger the forces are the higher the boiling point will be..11/19/2010 S.Martinez 65
  66. 66. 11/19/2010 S.Martinez 66
  67. 67. PREDICTING POLARIT Y11/19/2010 S.Martinez 67
  68. 68. PREDICTING POLARIT Y11/19/2010 S.Martinez 68
  69. 69. MOLECULAR POLARIT Y11/19/2010 S.Martinez 69