Early Quantum Theory and Models of the Atom

1
Chapter 27

• Early Quantum Theory and Models of the Atom

2
The Atom

• Protons Found in the Nucleus
• Carry a Positive Charge
• Have a Mass of 1 x 10-27 kg
• Neutrons Found in the Nucleus
• Carry no charge
• Have a mass that is approximately the same as a
  Proton
• Electrons travel around the nucleus in specific
  orbits related to their energy
• Carry a negative charge
• Have a mass of 9 x 10-31 kg

3
Light Quanta

• Light has a dual nature it is made up of
  packets of energy called quanta or photons which
  are carried on a wave.
• When an atom absorbs energy electrons move from
  their normal or ground state to a higher energy
  or excited state. To go back to their ground
  state atoms give off this excess energy as light.

4
The Energy of a Photon

• The energy of any photon of light given off in
  this way is determined by the equation
• E hf
• Where E energy in joules
• h 6.626 x 10-34 Js (Plancks Constant)
• f frequency of the light

5
The Photoelectric Effect

• The photoelectric effect is the ejection of
  electons from a material when light falls upon
  it.
• The material is sensitive to the frequency of the
  light not its intensity.

6
Supplementary Material

• Light and Color

7
The Colors of Light

• Light is defined as the frequencies of
  electromagnetic radiation which stimulate the
  human retina.
• Light ranges in color from
• Red - lowest frequency/longest wavelength
• Orange
• Yellow
• Green
• Blue
• Indigo
• Violet highest frequency/shortest wavelength

8
White Light and the Color Black

• White light contains all of the colors
  (frequencies) of visible light.
• Black is the absence of light.
• Vision is the process of seeing reflected light.
  The color that you see is reflected from an
  objects all other wavelengths are absorbed.

9
Color by Transmission

• The color of a transparent object depends upon
  the color it transmits.
• The material which selectively absorbs colors of
  light is called a pigment.
• Absorbed light warms the object hence darker
  colors tend to get warm in sunlight and lighter
  colors tend to remain cooler.

10
Mixing Light

• When red, blue and green light (primary colors)
  are mixed, new colors are formed (secondary
  colors).
• All three colors form white light.
• Red and Green yellow
• Red and Blue magenta
• Green and Blue - Cyan

11
Mixing Pigments

• When you mix pigments (paints) you add by
  subtraction that is each pigment you add to
  your mixture subtracts a color of light.
• Primary pigments
• Magenta
• Yellow
• Cyan
• Secondary Mixtures
• Yellow and Cyan Green
• Yellow and Magenta Red
• Magenta and Cyan - Blue