PowerPoint Presentation - History and Models of the Atom - PowerPoint

							Electrons and Quantization
1. Atom Changes in Reactions

chemical reactions only involve the
 electrons of atoms
   the nucleus of atoms are not affected when
    atoms rearrange themselves
as two atoms approach each other, the
 (negative) electrons become attracted by
 both (positive) nuclei of the atoms
   which can result in ionic or covalent bonds
  2. Light
 the visible light spectrum is a rainbow of colours:
 2. Light

 Wavelength (λ) and Frequency (f) are related by:

                                c
                           f            constant = speed of light
                                
          if frequency goes up, wavelength goes down
 Frequency and Energy are related by:
                                                   also a constant
                           E  hf                 (Plank’s constant)

          if frequency goes up, energy goes up
 2. Light
 violet light has (relatively) high energy and a high
  frequency
 red light has a (relatively) low energy and low
  frequency
 if you ever forget…think about ultraviolet and
  infrared
                                   above - ie “above violet”
    below - ie “below red”


    also remember the light from a Bunsen burner - which
     is hotter?
2. Light

all electromagnetic radiation (including
 light) has some interesting properties:
      massless
      can travel through a vacuum
      travels at ~300,000 km/s
      the energy is QUANTIZED
3. Origin of the Quantized Energy

recall our Bohr model of the atom:




      each “orbit” has a different energy
         the further from the nucleus, the HIGHER the energy
      if electrons move between orbits their energy
       changes
  consider this:




                   +



    calvin             sugar                “excited” calvin




                                        +



“excited” calvin       energy release       “relaxed” calvin
                    n=2
                            electron
          n=1


              +   energy




atom                                        excited atom

  when atoms absorb energy their electrons go to a
higher orbital are “raised up” - they have more energy
                                  energy +
                                 (as light)



excited atom                                       relaxed atom


    when atoms lose energy their electrons “fall down”
                          just like when you drop something
  this is how fluorescent lights, neon lights, and lasers work
   depending on the size of the “jump”,
    different light energies are given off
  if electrons
move towards
 the nucleus,
 they give off
     energy




  if electrons
move away from
 the nucleus,
    they gain
     energy
 3. Origin of the Quantized Energy

 Here’s a story:
   a “ground state” atom gains energy, which pushes it’s
    electrons up to a higher orbital
       a ground state atom has all of it’s electrons in the lowest
        possible energy orbits
   this atom is now in an “excited state”
   the electron jumps back down, and gives off energy in
    the form of light
 note: this is NOT why a green shirt looks green
   …but this IS why a green laser looks green
Homework

page 124 - #5,6
read page 128




  do you understand why the energy is quantized?
Lab Comments                       What was the point?

  why did we just measure the thickness
   of one page?

  why did we stir the heating liquid?
    heating liquids are stirred to avoid
     “bumping”


  why was the solid Ca(OH)2 was rinsed
   with water
                          lab 1A questions:
                              analysis: 3
 Lab Data                     follow-up: 2, 4, 5


mass of 1 pin / 30 pins             mass of 150 mL beaker