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Bonding Theory II

Bonding Theory II. BONDS INNNNN SPAAAAAAACE! The behavior of molecules is based on the structure of its bonding. Bonding Theory II. Lewis Dot Diagrams: Valence electrons arranged to show how each atom fills its outer shell. Bonding Theory II. Lewis Dot Diagrams.

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Bonding Theory II

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  1. Bonding Theory II • BONDS INNNNN SPAAAAAAACE! • The behavior of molecules is based on the structure of its bonding.

  2. Bonding Theory II • Lewis Dot Diagrams: • Valence electrons arranged to show how each atom fills its outer shell.

  3. Bonding Theory II • Lewis Dot Diagrams. • For all atoms that form covalent bonds, except hydrogen, 8 electrons represents a full outer level.

  4. Bonding Theory II • Lewis Dot Diagrams. • Shared pairs - 2 electrons shared in bonding. • Unshared pairs - 2 electrons not involved in bonding.

  5. Lewis Diagrams • Process: 1. Add up all the valence e-. 2. Connect the atoms and subtract 2 e- for each bond. 3. Fill in e- pairs to complete the octets.

  6. Lewis Diagrams • Process: 4. If you run out of e-, then use multiple bonds (double or triple bonds). 5. If you have too many e-, then expand the octet.

  7. Bonding Theory II • Ex. p. 323. • 1a.) H2Te • 1c.) NI3 • 1d.) CBr4

  8. Electron Pair Repulsion • Electron pairs spread out as far as possible to minimize repulsive forces. • Pauli - only 2 electrons of opposite spins may share the same orbital.

  9. Electron Pair Repulsion • Parallel spinning electrons may not. They repel. In fact, the electron-electron repulsion formed by different charge clouds is greater than the normal electrostatic repulsion.

  10. Electron Pair Repulsion • Thus, unshared pairs will alter molecular shape and bond angles.

  11. Electron Pair Repulsion • Unshared-unshared repulsion > unshared-shared repulsion > shared-shared repulsion > 2 electrons in the same orbital.

  12. Electron Pair Repulsion • Bond angles with no unshared pairs: • linear, trigonal planar, and tetrahedral molecules • Other shapes (like trigonal bipyramidal, octahedral)

  13. Electron Pair Repulsion • Bond angles with unshared pairs: • linear molecules • Trigonal pyramidal • Bent molecules • P. 325

  14. Electron Pair Repulsion • Bonds involving atoms with unshared pairs, will result in angles that are less than expected.

  15. Electron Pair Repulsion • Ex. HCl • Ex. BeF2 • Ex. H2O • Ex. CH4 • Ex. NH3

  16. Hybrid Orbitals • Atoms form hybrid orbitals before covalent bonding. • The s and p orbitals blend to form a hybrid orbital. • sp3 , sp2, sp

  17. Hybrid Orbitals • sp3: used in C-C single bonds (angle = 109.5) • sp2: used in double bonds (angle = 120) • sp: used in triple bonds (angle = 180)

  18. Sigma and Pi bonds • Sigma bond - the overlap of two orbitals that lie directly on the same bond axis. • Single bonds are composed of a sigma type bond.

  19. Sigma and Pi bonds • Pi bonds occur when two p orbitals overlap parallel to each other.

  20. Sigma and Pi bonds • Double bonds consist of one sigma and one pi bond. • Triple bonds consist of one sigma and two pi bonds. • See pg. 331 for examples.

  21. Lewis Dot II • Double bonds - a bond composed of two pairs of shared electrons. • Triple bonds - three pairs. • Ex. Ethene, N2

  22. Lewis Dot II • Benzene Ring • A cyclohexyl structure with alternating double bonds. • Results in delocalized p-orbital electrons.

  23. Lewis Dot II • Benzene Ring • Conjugated system a form of resonance with alternating double bonds. • Resonance: when more than one structural formula is needed to explain a molecule.

  24. Organic stuff • Organic Nomenclature: • Alkanes w/ substituted groups • Alkenes, alkynes, cycloalkanes • Alcohols and ethers

  25. Organic stuff • Organic Nomenclature: • Alkyl Halides, Aldehydes, Ketones, Esters, Carboxylic Acids

  26. Organic stuff • Saturated compound - a hydrocarbon having only single bonds. • Unsaturated - a hydrocarbon having at least one multiple bond.

  27. Organic stuff • Functional groups - an addition to a hydrocarbon chain that distinguishes the organic compound. • Ex. -OH = alcohols

  28. Organic stuff • Be able to write the condensed, straight bond (skeletal structure), bent bond (bond line structure), and lewis dot structures for a given organic molecule.

  29. Isomerism • Isomerism occurs when two molecules have the same molecular formula but different chemical structures.

  30. Isomerism • Structural isomers - alteration in the carbon chain. • Ex. Pentane, 2-methyl butane, 2,2-dimethyl propane

  31. Isomerism • Positional isomers - the position of a multiple bond differs. • Ex. 1-butene Vs. 2-butene

  32. Isomerism • Functional isomers - the position of a functional group differs. • Ex. 1-butanol Vs. 2-butanol

  33. Isomerism • Geometric isomers - the order of the bonding of the atoms are the same, but with a different arrangement around a double bond.

  34. Isomerism • Geometric isomers - cis Vs. trans. • Ex. Cis-2-pentene Vs. Trans-2-pentene

  35. Isomerism • Chirality - handedness, the molecules differ by being non-superimposable mirror images of each other.

  36. Bond Angle Summary • See p. 341. • Octahedral organo-metalic ligands: secondary bonding results in an octahedral crystal surrounding a central metal.

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