Transcript Chapter 27 Early Quantum Theory and Models of the Atom

Chapter 27
Early Quantum Theory and Models
of the Atom
The Atom
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Protons – Found in the Nucleus
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Neutrons – Found in the Nucleus
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Carry a Positive Charge
Have a Mass of 1 x 10-27 kg
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
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Carry a negative charge
Have a mass of 9 x 10-31 kg
Light Quanta
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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.
The Energy of a Photon
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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 J•s (Planck’s Constant)
f = frequency of the light
The Photoelectric Effect
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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.
Supplementary Material
Light and Color
The Colors of Light
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Light is defined as the frequencies of
electromagnetic radiation which stimulate the
human retina.
Light ranges in color from:
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Red - lowest frequency/longest wavelength
Orange
Yellow
Green
Blue
Indigo
Violet – highest frequency/shortest wavelength
White Light and the Color
Black
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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.
Color by Transmission
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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.
Mixing Light
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When red, blue and green light
(primary colors) are mixed, new colors
are formed (secondary colors).
All three colors form white light.
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Red and Green – yellow
Red and Blue – magenta
Green and Blue - Cyan
Mixing Pigments
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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
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Magenta
Yellow
Cyan
Secondary Mixtures
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Yellow and Cyan – Green
Yellow and Magenta – Red
Magenta and Cyan - Blue