Ep 24: Bonding Models and Lewis Structures

Definition of Model

  • model = representation of something (physical or conceptual)
    • Models allow you to experience things you couldn’t otherwise experience, stuff which is too big to see like the solar system, too small like a cell or doesn’t exist like the Golden Snitch
  • Models simplify reality to free our minds to do bigger and better things

Why and How do Atoms Bond?

  • Why do Atoms Bond?
    • molecule(bonded atoms) = a group of atoms
      • atoms want to minimise energy, so groups of atoms hang close together
  • How do Atoms Bond?
    • bond = a bunch of electrons shared electrons connecting atoms
      • electrons constantly move but in a predictable pattern
      • Spend most time in 1 area
      • Like the garden cat, which constantly moves from garden to garden but will predictably spend most time in its owners garden (even if it shits in yours)
    • covalent bond = electrons spend most time in-between nuclei
      • nuclei <3 electrons
      • nuclei end up close together
      • Like dogs who drag different owners together. Even if the owners do not like each other, they end up close together

History of Atomic Models

  • einstein = thought atoms were sticky
  • jons = discovered certain chemicals have charges, thought charges joined atoms
  • Lewis = Atoms share specific electrons, forming bonds.
    • 1890 discovery of electrons
  • Linus Pauling = Chemical bonds are a overlapping of each atom’s individual electron-cloud
    • rather than bonds between specific electrons (lewis)
    • Electrons in constant movement, but spend most time in 1 area (as described above), e.g. in covalent spend most time between nuclei

Lewis-Dot Model

  • 2-D model that represents covalent bonds as straight lines and unbounded valence electrons as dots
    • valence electrons = electrons in outer-shell
    • straight lines = bonded pairs (shared valence electrons)
    • dots = lone pairs (unshared valence electrons)
      • Valence pair only attached to one atom
  • Octet Rule
    • Atoms most stable with filled shell
    • For many atoms this takes 8 electrons, so called octet rule
      • Only applies to rows 1&2. Exceptions are Hydrogen (1 electron) and all rows from 3 and beyond

Drawing models

  • Ionic bonds
    • Also represents ionic bonds
    • NaCl
      • Na is a metal, so bond is ionic, so electron is transferred
    • All dots and no lines because not a covalent bond
  • covalence bonds
  • How to figure out bonds
    1. Calculate Total Valence Electrons
    2. Create Bonds
    3. Fill shells with remaining electrons
    • If amount of electrons/lone-pairs required to fill shells is more than Total Valence Electrons, then increase bonds!
    • The more bonds you have the less lone pairs you need to fill shells
      • The more lines between atoms, the less dots you need to fill shells
    • valence electrons - bond = remaining electron
  • Single Bond = H20
    1. Calculate Total Valence Electrons
      • H: 1 valence x 2 atoms = 2
      • O: 6 valence x 1 atom = 6
      • total = 8 Valence Electrons
    2. Create Bonds
      • Neither Hydrogen or Oxygen have enough electrons to be stable, so they share to make up the lack…sharing creates a bond
      • Single Bond between each Hydrogen and Oxygen
      • valence electrons - bond = remaining electron
      • 8 - 4 = 4
    3. Fill Shell
      • Hydrogen requires 1 valence electron, bond fills shell
      • Oxygen requires 6 valence electrons, bond only fills 2, use remaining four
    • Water contains two bonds and two lone pairs
  • Double Bond = C02
    1. Calculate Total Valence Electrons
      • C: 4 valence x 1 atoms = 4
      • O: 6 valence x 2 atom = 12
      • total = 16 Valence Electrons
    2. Create Bonds
      • Single Bond between each Oxygen and Carbon
        • Filling Shells = 20 valence electrons!
        • Not enough Electrons remain to fill shells!
      • Double Bond between each oxygen and Carbon
        • All four bonded atoms count towards both atom’s octects
    3. Fill Shell
      • Carbon requires 4 valence electrons, bond fills shell
      • Oxygen requires 6 valence electrons, bond only fills 2, use remaining four
    • CO2 contains 2 double bonds and two lone pairs on each oxygen
  • Triple Bond = N2
    1. Calculate Total Valence Electrons
      • N: 5 valence x 1 atoms = 5
      • N: 5 valence x 1 atom = 5
      • total = 5 Valence Electrons
    2. Create Bonds
      • Triple Bond is required
        • Each atom shares 6 electrons, 3 in each shell
    3. Fill Shell
      • Nitrogen requires 5 valence electrons, bond fills 3, use remaining four (2 lone pairs each)
    • N2 contains a triple bond and a lone pair on each atom
    • Triple Bond is why molecular nitrogen is so difficult to break apart to form fertilizer and stuff
  • Three is maximum Number of bonds