Chemical Bonding

  1. What is a Bond
    1. The forces holding atoms and molecules together
  2. Why Study Bonding
    1. Learn nature of molecules
      1. State of matter
      2. Energy stored in bond
    2. What will combine
      1. Shape
      2. Energy requirements
  3. Octet Rule
    1. Atoms form bonds to obtain stable configuration of noble gas
    2. 8 electrons in outer orbit (s and p sublevels)
    3. Number of bonds formed equals number of unpaired electrons
  4. Electronegativity (EN)
    1. The tendency to attract electrons in bonds
    2. Tug of war for electrons
    3. Electrons move toward highest EN
  5. Influenced by:
    1. Distance from nucleus
    2. Shielding effect
    3. Full or ½ full sublevels
    4. Increased nuclear charge
  6. Activity
    1. Most active metals have low EN
    2. Most active non-metals have high EN
  7. Bond Strength
    1. Direct variation with difference in EN
  8. Bond Character
    1. Degree of difference inverse to degree of sharing
    2. Degree of sharing determines type of bond
    3. Handout - save for test/exam
  9. Bond Energy
    1. Energy required to break bond
    2. Measure of strength of bond
    3. Difference in bond energies of product/reactant determine energy needs
    4. End product of reaction has lower energy
  10. Bond Types: Ionic
    1. Form between dissimilar materials
    2. Difference in EN > 2.0
    3. Atom with greater EN takes electrons
    4. Atoms form ions
    5. Electrostatic forces hold ions together
      1. Form crystals
      2. High melting points
    6. Conduct electricity in solution
    7. Soluble in water
  11. Bond Types: Covalent
    1. Form between similar materials
    2. Differnce in EN < 0.5
    3. Atoms share electrons, form molecules normally happens between non-metals
    4. Characteristics
      1. Low melting/boiling points
      2. Do not conduct
      3. Brittle
    5. Even sharing produces non-polar bond
    6. Uneven sharing produces polar bond
    7. Definitions
      1. Bond axis: line joining atoms
      2. Bond angle: angle between bond axes (determined by properties of central atom, number of valence electrons)
      3. Bond length: separation between atoms (increases with atomic number)
    8. Bond Movements
      1. Bond length not fixed, atoms act as if on springs
      2. Stretching
      3. Bending
      4. Rotating
    9. Spectroscopy
      1. Atoms absorb/transmit radiation in unique patterns
      2. IR spectra determined by vibration frequency of bond
      3. MW spectra determined by rotations (mass)
  12. Bond types: Polar Bond
    1. 0.5
    2. Forms when molecule forms dipole
    3. Charge is unevenly distributed
    4. Positive portion of one molecule attracts negative end of another
    5. Hydrogen bond special case
      1. Hydrogen attracted to very electronegative atom
      2. 1/10 strength of normal bond
      3. Keeps water liquid in normal temperature range
      4. Holds DNA in double helix
  13. Types of Bonds: Metallic Bond
    1. Atoms have same electronegativity
    2. Form crystals with each atom surrounded by 8-12 atoms
    3. Atoms overlap, electrons move between atoms
    4. Moving electrons conduct heat and electricity
    5. Electrons react with light (luster)
    6. Atoms readily rearrange as electrons flow to new positions
  14. What Drives Structure
  15. Types of Electrons
  16. Lewis Diagrams>/li>
  17. Valence Shell Electron Pair Repulsion
  18. Shape of Molecule
  19. Repulsive Forces
  20. Linear Molecules (180º)
  21. Trigonal Planar (120º)
  22. Tetrahedron (109.5º)
  23. Pyramidal (107º)
  24. Bent Pyramid (105º)
  25. Multiple Central Atoms
    1. Pairs around each atom determine shape of parts of molecule
    2. Each may be different
  26. Analysis of Compound
    1. Determine number of shared and unshared pairs
    2. Assign shapes/angles using VSEPR theory
  27. Polarity
  28. Analysis of Polarity
    1. Draw structural formula
    2. Check relative electronegativity
    3. Label charge direction for individual bonds
    4. Label charge direction for entire molecule
  29. Water
  30. Large Molecules
1