CHEM 205 lecture 10

• Covalent bonding


  Equal sharing, no separation of charge
• Polar covalent bonding


  Unequal sharing, partial separation of charge
• Ionic bonding


  No sharing, complete separation of charges
• Electronegativity


  Ability of an atom or molecule to attract shared electrons to itself
• Electronegativity is higher for nonmetals, lower for metals
• As you go to the right of the periodic table and up, the electronegativity increases
• Polar molecules


  • Interact strongly with each other because of electrostatic attractions
  • Have higher surface tension and resist flowing
  • Interact with electric fields
  • Dissolve well in other polar substances
• Nonpolar molecules


  • Interactions are very weak with each other
  • Easier to melt and boil
  • Have lower surface tension and flow easily
  • Dissolve in other nonpolar substances only
• Bond dipoles


  View of how bonding electrons are distributed between atoms, only deals with shared electrons
• Formal charges


  Helps visualize atom's place on electron richness or poorness, only deals with lone electrons
• Quantum mechanics was a revolution of physics in the 1900-1930's
• Electromagnetic radiation


  Light, radiant energy that behaves as waves

  
• Speed of light


  Distance of 2 peaks in meters multiplied by number of waves passing per second
• Wavelength 1 > wavelength 2

  Frequency 1 < frequency 2

  
• Higher frequency


  Higher energy
• Lower frequency


  Lower energy
• Shorter wavelength


  Higher energy
• Longer wavelength


  Lower energy
• Photoelectricity


  Energy required to rip an electron off a metal atom
• Photons


  Light travels in energy packets

  
• Higher intensity light


  More photons hit metal, more electrons get ejected, more current

  
• Energy of each photon


  Proportional to light's frequency