Kimia Umum (6)

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Kimia Umum (6)

  1. 1. Sesion#06Chemical Bonding<br />Irma<br />Jurusan Kimia<br />FakultasMatematikadanIlmuPengetehuanAlam<br />06/01/2011<br />1<br />© 2010 Universitas Negeri Jakarta | www.unj.ac.id |<br />
  2. 2. Chemical Bonding<br />Lewis<br />VSEPR shapes<br />AXE notation<br />Polarity<br />06/01/2011<br />© 2010 Universitas Negeri Jakarta | www.unj.ac.id |<br />2<br />
  3. 3. <ul><li>Mahasiswa dapat memahami konsep pembentukan ikatan kimia.</li></ul>Outline<br />06/01/2011<br />© 2010 Universitas Negeri Jakarta | www.unj.ac.id |<br />3<br />
  4. 4. Indikator<br />Menjelaskan Konsep Pembentukan ikatan kimia dan Peranan Elektron Valensi dalam Pembentukan Ikatan Kimia<br />Menjelaskan aturan Oktet dan struktur Lewis serta memberikan contohnya<br />Menjelaskan pengertian ikatan ion, kovalen, kovalen koordinat dan logam<br />Menjelaskan bentuk resonansi<br />Menjelaskan teori VSEPR <br />06/01/2011<br />© 2010 Universitas Negeri Jakarta | www.unj.ac.id |<br />4<br />
  5. 5. Valence Electrons<br />06/01/2011<br />© 2010 Universitas Negeri Jakarta | www.unj.ac.id |<br />5<br />1A<br />2A<br />3A<br />4A<br />5A<br />6A<br />7A<br />Number of valence electrons is equal to the Group number.<br />
  6. 6. The Octet Rule<br />The Octet Rule<br />All noble gases except He has an s2p6 configuration. <br />Octet rule: atoms tend to gain, lose, or share electrons until they are surrounded by 8 valence electrons (4 electron pairs).<br />Caution: there are many exceptions to the octet rule.<br />06/01/2011<br />© 2010 Universitas Negeri Jakarta | www.unj.ac.id |<br />6<br />
  7. 7. Exceptions to the Octet Rule<br />Central Atoms Having Less than an Octet<br />Relatively rare.<br />Molecules with less than an octet are typical for compounds of Groups 1A, 2A, and 3A.<br />Most typical example is BF3 (Boron triflouride).<br />Formal charges indicate that the Lewis structure with an incomplete octet is more important than the ones with double bonds.<br />06/01/2011<br />© 2010 Universitas Negeri Jakarta | www.unj.ac.id |<br />7<br />
  8. 8. BF3<br />Exceptions to the Octet Rule<br />06/01/2011<br />© 2010 Universitas Negeri Jakarta | www.unj.ac.id |<br />8<br />
  9. 9. Exceptions to the Octet Rule<br />Central Atoms Having More than an Octet<br /><ul><li>This is the largest class of exceptions.
  10. 10. Atoms from the 3rd period onwards can accommodate more than an octet.
  11. 11. Beyond the third period, the d-orbitals are low enough in energy to participate in bonding and accept the extra electron density.</li></ul>06/01/2011<br />© 2010 Universitas Negeri Jakarta | www.unj.ac.id |<br />9<br />
  12. 12. Drawing Lewis Structures<br />Follow Step by Step Method <br />Total all valence electrons. [Consider Charge]<br />Write symbols for the atoms and guess skeleton structure [ define a central atom ]. <br />Place a pair of electrons in each bond.<br />Complete octets of surrounding atoms. [ H = 2 only ] <br />Place leftover electrons in pairs on the central atom.<br />If there are not enough electrons to give the central atom an octet, look for multiple bonds by transferring electrons until each atom has eight electrons around it.<br />06/01/2011<br />© 2010 Universitas Negeri Jakarta | www.unj.ac.id |<br />10<br />
  13. 13. Lewis Symbols<br />06/01/2011<br />© 2010 Universitas Negeri Jakarta | www.unj.ac.id |<br />11<br />
  14. 14. 1. Decide on the central atom; never H.<br /> Central atom is atom of lowest affinity for electrons.<br /> In ammonia, N is central<br /> 2. Count valence electrons<br /> H = 1 and N = 5<br /> Total = (3 x 1) + 5 <br /> = 8 electrons or<br />Building a Dot Structure<br />06/01/2011<br />© 2010 Universitas Negeri Jakarta | www.unj.ac.id |<br />12<br />Ammonia, NH3<br />4 pairs<br />
  15. 15. ••<br />H<br />H<br />N<br />H<br />3. Form a sigma bond <br /> between the central atom <br /> and surrounding atoms.<br />4. Remaining electrons form <br /> LONE PAIRS to complete <br />octet as needed.<br /> 3 BOND PAIRS and 1 LONE PAIR.<br />Note that N has a share in 4 pairs (8 electrons), while <br />each H shares 1 pair.<br />Building a Dot Structure<br />06/01/2011<br />© 2010 Universitas Negeri Jakarta | www.unj.ac.id |<br />13<br />
  16. 16. Sulfite ion, SO32-<br />Step 1. Central atom = S<br />Step 2. Count valence electrons<br /> S = 6<br /> 3 x O = 3 x 6 = 18<br /> Negative charge = 2<br /> TOTAL = 6 + 18 + 2 = 26 e- <br /> or 13 pairs<br />Step 3. Form sigma bonds<br />10 pairs of electrons are left.<br />06/01/2011<br />© 2010 Universitas Negeri Jakarta | www.unj.ac.id |<br />14<br />
  17. 17. 06/01/2011<br />© 2010 Universitas Negeri Jakarta | www.unj.ac.id |<br />15<br />••<br />O<br />•<br />•<br />•<br />•<br />••<br />••<br />O<br />O<br />S<br />•<br />•<br />•<br />•<br />••<br />••<br />••<br />Sulfite ion, SO32- (2)<br />Remaining pairs become lone pairs, <br /> first on outside atoms<br /> then on central atom.<br />Each atom is surrounded by an octet of electrons.<br />NOTE - must add formal charges (O-, S+) for complete dot diagram<br />
  18. 18. Carbon Dioxide, CO2<br />1. Central atom = __C____<br />2. Valence electrons = _16_ or _8_ pairs<br />3. Form sigma bonds.<br />06/01/2011<br />© 2010 Universitas Negeri Jakarta | www.unj.ac.id |<br />16<br /> This leaves __6__ pairs.<br />4. Place lone pairs on outer atoms.<br />
  19. 19. Carbon Dioxide, CO2 (2)<br />4. Place lone pairs on outer atoms.<br />06/01/2011<br />© 2010 Universitas Negeri Jakarta | www.unj.ac.id |<br />17<br />5. To give C an octet, form DOUBLE BONDS <br />between C and O.<br />The second bonding pair forms a pi (p)bond.<br />
  20. 20. H2CO<br />SO3<br />Double and even triple bonds are commonly observed for C, N, P, O, and S<br />06/01/2011<br />© 2010 Universitas Negeri Jakarta | www.unj.ac.id |<br />18<br />C2F4<br />
  21. 21. Sulfur Dioxide, SO2<br />1. Central atom = S<br />2. Valence electrons = 6 + 2*6 = 18 electrons<br /> or 9 pairs<br />06/01/2011<br />© 2010 Universitas Negeri Jakarta | www.unj.ac.id |<br />19<br />3. Form pi () bond so that S has an octet <br /> — note that there are two ways of doing this.<br />
  22. 22. Sulfur Dioxide, SO2<br />06/01/2011<br />© 2010 Universitas Negeri Jakarta | www.unj.ac.id |<br />20<br />Equivalent structures called:<br />RESONANCE <br />STRUCTURES<br />The proper Lewis structure<br /> is a HYBRID of the two.<br />A BETTER representation of SO2<br />is made by forming 2 double bonds<br />Each atom has<br /> - OCTET<br /> - formal charge = 0<br />O = S = O<br />
  23. 23. Urea (NH2)2CO<br />06/01/2011<br />© 2010 Universitas Negeri Jakarta | www.unj.ac.id |<br />21<br />1. Number of valence electrons = 24 e-<br />2. Draw sigma bonds.<br />Leaves 24 - 14 = 10 e- pairs.<br />3. Complete C atom octet with double bond.<br />4. Place remaining electron pairs on oxygen<br />and nitrogen atoms.<br />
  24. 24. Sulfur Tetrafluoride, SF4<br />Central atom = S<br />Valence electrons = 6 + 4*7 = 34 e-<br /> or 17 pairs.<br />Form sigma bonds and distribute electron pairs.<br />06/01/2011<br />© 2010 Universitas Negeri Jakarta | www.unj.ac.id |<br />22<br />5 pairs around the S atom. A common occurrence outside the 2nd period. <br />
  25. 25. Formal Charge<br /><ul><li>Consider:
  26. 26. For C:
  27. 27. There are 4 valence electrons (from periodic table).
  28. 28. In the Lewis structure there are 2 nonbonding electrons and 3 from the triple bond. There are 5 electrons from the Lewis structure.
  29. 29. Formal charge: 4 - 5 = -1.</li></ul>Drawing Lewis Structures<br />06/01/2011<br />© 2010 Universitas Negeri Jakarta | www.unj.ac.id |<br />23<br />
  30. 30. Formal Charge<br /><ul><li>Consider:
  31. 31. For N:
  32. 32. There are 5 valence electrons.
  33. 33. In the Lewis structure there are 2 nonbonding electrons and 3 from the triple bond. There are 5 electrons from the Lewis structure.
  34. 34. Formal charge = 5 - 5 = 0.
  35. 35. We write:</li></ul>Drawing Lewis Structures<br />06/01/2011<br />© 2010 Universitas Negeri Jakarta | www.unj.ac.id |<br />24<br />
  36. 36. <ul><li>According to the Lewis model
  37. 37. an atom may lose or gain enough electrons to acquire a filled valence shell and become an ion. An ionic bond is the result of the force of attraction between a cation and an anion.
  38. 38. an atom may share electrons with one or more other atoms to acquire a filled valence shell. A covalentbond is the result of the force of attraction between two atoms that share one or more pairs of electrons.
  39. 39. Metallic bond: attractive force holding pure metals together.</li></ul>Chemical Bonds<br />06/01/2011<br />© 2010 Universitas Negeri Jakarta | www.unj.ac.id |<br />25<br />
  40. 40. Ionic Bonding<br />06/01/2011<br />© 2010 Universitas Negeri Jakarta | www.unj.ac.id |<br />26<br />
  41. 41. Ionic Bonding<br />Between atoms of metals and nonmetals with very different electronegativity<br />Bond formed by transfer of electrons<br />Produce charged ions all states. Conductors and have high melting point.<br />Examples; NaCl, CaCl2, K2O<br />06/01/2011<br />© 2010 Universitas Negeri Jakarta | www.unj.ac.id |<br />27<br />
  42. 42. 06/01/2011<br />© 2010 Universitas Negeri Jakarta | www.unj.ac.id |<br />28<br />
  43. 43. Electron from Na is transferred to Cl, this causes a charge imbalance in each atom. The Na becomes (Na+) and the Cl becomes (Cl-), charged particles or ions. <br />Ionic Bonding<br />06/01/2011<br />© 2010 Universitas Negeri Jakarta | www.unj.ac.id |<br />29<br />
  44. 44. Covalent Bonding<br />06/01/2011<br />© 2010 Universitas Negeri Jakarta | www.unj.ac.id |<br />30<br />
  45. 45. Covalent Bonding<br />A chemical bond in which 2 atoms share a single of electron to form one bond.<br />Two nonmetal atoms form a covalent bond because they have less energy after they bonded<br /> H+H H: H = HH = H2<br />hydrogen molecule<br />06/01/2011<br />© 2010 Universitas Negeri Jakarta | www.unj.ac.id |<br />31<br />
  46. 46. 06/01/2011<br />© 2010 Universitas Negeri Jakarta | www.unj.ac.id |<br />32<br />
  47. 47. Covalent Bonding<br />Between nonmetallic elements of similar electronegativity<br />Formed by sharing electron pairs<br />Stable non-ionizing particles, they are not conductors at any state<br />Examples; O2, CO2, C2H6, H2O, SiC<br />06/01/2011<br />© 2010 Universitas Negeri Jakarta | www.unj.ac.id |<br />33<br />
  48. 48. Covalent Bonds<br />06/01/2011<br />© 2010 Universitas Negeri Jakarta | www.unj.ac.id |<br />34<br />
  49. 49. Double Covalent Bonding<br />2 pairs of electrons are shared between 2 atoms<br />Example O2 <br />06/01/2011<br />© 2010 Universitas Negeri Jakarta | www.unj.ac.id |<br />35<br />     <br /> O  + O  O::O<br />    <br /> double bond<br />
  50. 50. Triple Covalent Bonding<br />3 pairs of electrons are shared between 2 atoms<br />Example N2<br />06/01/2011<br />© 2010 Universitas Negeri Jakarta | www.unj.ac.id |<br />36<br />     <br /> N  + N  N:::N<br /><br />triple bond<br />
  51. 51. Type of Covalent Bonding<br /><ul><li>Atoms and molecules have 3 dimensions
  52. 52. Shapes of molecules lead to additional properties of covalent compounds
  53. 53. Polar covalent Bonding
  54. 54. When electrons are not shared equally between two atoms
  55. 55. Bond that is certain % ionic
  56. 56. Nonpolar covalent Bonding
  57. 57. Electrons are shared equally
  58. 58. Diatomic atoms </li></ul>06/01/2011<br />© 2010 Universitas Negeri Jakarta | www.unj.ac.id |<br />37<br />
  59. 59. Nonpolar Covalent Bonding<br /><ul><li>Electrons are shared between atoms with the same electronegativity values.
  60. 60. Difference = 0
  61. 61. Examples: N2, Br2, O2</li></ul>06/01/2011<br />© 2010 Universitas Negeri Jakarta | www.unj.ac.id |<br />38<br />
  62. 62. Oxygen Atom<br />Oxygen Atom<br />Oxygen Molecule (O2)<br />Two atoms share one or more pairs of outer-shell electrons<br />06/01/2011<br />© 2010 Universitas Negeri Jakarta | www.unj.ac.id |<br />39<br />
  63. 63. Polar Covalent Bonding<br /><ul><li>Electrons are shared between different nonmetal atoms.
  64. 64. Examples: O-Cl, O-S, N-Cl, H2O</li></ul>06/01/2011<br />© 2010 Universitas Negeri Jakarta | www.unj.ac.id |<br />40<br />
  65. 65. Water is a polarmolecule because oxygen is more electronegative than hydrogen, and therefore electrons are pulled closer to oxygen.<br />06/01/2011<br />© 2010 Universitas Negeri Jakarta | www.unj.ac.id |<br />41<br />
  66. 66. Diatomic Elements<br />Elements that are naturally in molecules with 2 atoms each.<br />HONClBrIF (pneumonic)<br />Existing as diatomic molecule yields a stable octet<br />Gases that exist as diatomic molecules are H2, F2, N2, O2, Cl2, Br2, I2<br />Examples Fluorine & Bromine<br />06/01/2011<br />© 2010 Universitas Negeri Jakarta | www.unj.ac.id |<br />42<br />
  67. 67. Chemical Bonds<br />06/01/2011<br />© 2010 Universitas Negeri Jakarta | www.unj.ac.id |<br />43<br />
  68. 68. 06/01/2011<br />© 2010 Universitas Negeri Jakarta | www.unj.ac.id |<br />44<br />
  69. 69. Strengths of Covalent Bonds<br />06/01/2011<br />© 2010 Universitas Negeri Jakarta | www.unj.ac.id |<br />45<br />
  70. 70. <ul><li>Bond in which only one atom donates electrons to form the bond
  71. 71. Sometimes an arrow is used to designate the coordinate covalent bond</li></ul>Coordinate Covalent Bonds<br />06/01/2011<br />© 2010 Universitas Negeri Jakarta | www.unj.ac.id |<br />46<br />
  72. 72. Coordinate Covalent Bonds<br />06/01/2011<br />© 2010 Universitas Negeri Jakarta | www.unj.ac.id |<br />47<br />
  73. 73. Metallic Bond<br />Formed between atoms of metallic elements<br />Bond found in metals, holds metal atoms together very strongly<br />Electron cloud around atoms <br />Good conductors at all states, lustrous, very high melting points<br />Examples; Na, Fe, Al, Au, Co<br />06/01/2011<br />© 2010 Universitas Negeri Jakarta | www.unj.ac.id |<br />48<br />
  74. 74. Ionic Bond, A Sea of Electron<br />06/01/2011<br />© 2010 Universitas Negeri Jakarta | www.unj.ac.id |<br />49<br />
  75. 75. Metals Form Alloys<br />06/01/2011<br />© 2010 Universitas Negeri Jakarta | www.unj.ac.id |<br />50<br /><ul><li>Metals do not combine with metals.
  76. 76. They form Alloys which is a solution of a metal in a metal.
  77. 77. Examples are steel, brass, bronze and pewter.</li></li></ul><li>Electronegativity<br /><ul><li>Electronegativity: The ability of one atoms in a molecule to attract electrons to itself.
  78. 78. Pauling set electronegativities on a scale from 0.7 (Cs) to 4.0 (F).
  79. 79. Electronegativity increases
  80. 80. across a period and
  81. 81. down a group.</li></ul>Electronegativity<br />06/01/2011<br />© 2010 Universitas Negeri Jakarta | www.unj.ac.id |<br />51<br />
  82. 82. Electronegativities of Elements<br />06/01/2011<br />© 2010 Universitas Negeri Jakarta | www.unj.ac.id |<br />52<br />
  83. 83. <ul><li>To decide whether a bond is covalent or ionic find the difference in electronegativities</li></ul>< 2.0 covalent and<br />> 2.0 ionic<br />Covalent or Ionic?<br />06/01/2011<br />© 2010 Universitas Negeri Jakarta | www.unj.ac.id |<br />53<br />
  84. 84. Electronegativity and Bond Polarity<br /><ul><li>There is no sharp distinction between bonding types.
  85. 85. The positive end (or pole) in a polar bond is represented + and the negative pole -.</li></ul>Bond Polarity and Electronegativity<br />06/01/2011<br />© 2010 Universitas Negeri Jakarta | www.unj.ac.id |<br />54<br />
  86. 86. Resonance Structures<br />06/01/2011<br />© 2010 Universitas Negeri Jakarta | www.unj.ac.id |<br />55<br />
  87. 87. 06/01/2011<br />© 2010 Universitas Negeri Jakarta | www.unj.ac.id |<br />56<br />
  88. 88. Molecular Shape and Molecular Polarity<br />06/01/2011<br />© 2010 Universitas Negeri Jakarta | www.unj.ac.id |<br />57<br />
  89. 89. Molecular Shape and Molecular Polarity<br />06/01/2011<br />© 2010 Universitas Negeri Jakarta | www.unj.ac.id |<br />58<br />
  90. 90. Covalent Bonding and Orbital Overlap<br />Lewis structures and VSEPR do not explain why a bond forms.<br />How do we account for shape in terms of quantum mechanics? <br />What are the orbitals that are involved in bonding?<br />We use Valence Bond Theory:<br />Bonds form when orbitals on atoms overlap.<br />There are two electrons of opposite spin in the orbital overlap.<br />06/01/2011<br />© 2010 Universitas Negeri Jakarta | www.unj.ac.id |<br />59<br />
  91. 91. Covalent Bonding and Orbital Overlap<br />06/01/2011<br />© 2010 Universitas Negeri Jakarta | www.unj.ac.id |<br />60<br />
  92. 92. 06/01/2011<br />© 2010 Universitas Negeri Jakarta | www.unj.ac.id |<br />61<br />
  93. 93. 06/01/2011<br />© 2010 Universitas Negeri Jakarta | www.unj.ac.id |<br />62<br />
  94. 94. <ul><li>To determine the electron pair geometry:
  95. 95. draw the Lewis structure,
  96. 96. count the total number of electron pairs around the central atom,
  97. 97. arrange the electron pairs in one of the above geometries to minimize e--e- repulsion, and count multiple bonds as one bonding pair.</li></ul>VSEPR Model <br />06/01/2011<br />© 2010 Universitas Negeri Jakarta | www.unj.ac.id |<br />63<br />
  98. 98. There are five fundamental geometries for molecular shape:<br />Molecular Shapes: VSEPR<br />06/01/2011<br />© 2010 Universitas Negeri Jakarta | www.unj.ac.id |<br />64<br />
  99. 99. Summary of VSEPR Molecular Shapes<br />06/01/2011<br />© 2010 Universitas Negeri Jakarta | www.unj.ac.id |<br />65<br />
  100. 100. The Effect of Nonbonding Electrons<br /><ul><li>By experiment, the H-X-H bond angle decreases on moving from C to N to O:
  101. 101. Since electrons in a bond are attracted by two nuclei, they do not repel as much as lone pairs.
  102. 102. Therefore, the bond angle decreases as the number of lone pairs increases</li></ul>VSEPR Model<br />06/01/2011<br />© 2010 Universitas Negeri Jakarta | www.unj.ac.id |<br />66<br />
  103. 103. Shapes of Larger Molecules<br /><ul><li>In acetic acid, CH3COOH, there are three central atoms.</li></ul>VSEPR Model<br />06/01/2011<br />© 2010 Universitas Negeri Jakarta | www.unj.ac.id |<br />67<br />
  104. 104. VSEPR Model<br />06/01/2011<br />© 2010 Universitas Negeri Jakarta | www.unj.ac.id |<br />68<br />
  105. 105. 06/01/2011<br />© 2010 Universitas Negeri Jakarta | www.unj.ac.id |<br />69<br />
  106. 106. 06/01/2011<br />© 2010 Universitas Negeri Jakarta | www.unj.ac.id |<br />70<br />
  107. 107. Thank You<br />06/01/2011<br />© 2010 Universitas Negeri Jakarta | www.unj.ac.id |<br />71<br />

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