2. Section 5.1 Light and Quantized Energy
Compare the wave and particle natures of light.
Define a quantum of energy, and explain how it is related to an energy change of matter.
Contrast continuous electromagnetic spectra and atomic emission spectra.
Light, a form of electronic radiation, has characteristics of both a wave and a particle.
Section 5-1

3. Summary of Atomic Theory
Year
Event
400BC
Democritus proposes idea of atom
1808
Dalton develops Atomic Theory
1897
Thomson uses cathode ray to discover electron, plum pudding model
1916
Millikan measures the mass of an e-
1919
Rutherford uses gold foil experiment to discover nucleus, proton

4. The Atom and Unanswered Questions
Recall that in Rutherford's model, the atom’s mass is concentrated in the nucleus and electrons move around it.
The model doesn’t explain how the electrons were arranged around the nucleus.
The model doesn’t explain why negatively charged electrons aren’t pulled into the positively charged nucleus.
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5. The Atom and Unanswered Questions (cont.)
In the early 1900s, scientists observed certain elements emitted visible light when heated in a flame.
Analysis of the emitted light revealed that an element’s chemical behavior is related to the arrangement of the electrons in its atoms.
Section 5-1

6. The Wave Nature of Light
electromagnetic radiation,
visible light
a form of energy that exhibits wave-like behavior as it travels through space
All waves can be described by several characteristics.
Section 5-1

7. The Wave Nature of Light (cont.)
wavelength (λ)
the shortest distance between equivalent points on a continuous wave
frequency (ν)
the number of waves that pass a given point per second
amplitude
the wave’s height from the origin to a crest
Section 5-1

8. The Wave Nature of Light (cont.)
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9. The Wave Nature of Light (cont.)
The speed of light (3.00  108 m/s) is the product of it’s wavelength and frequency c = λν.
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10. The Wave Nature of Light (cont.)
Wavelength and Frequency
inversely related
one gets bigger, the other gets smaller
different frequencies of light different colors
wide variety of frequencies (spectrum)

11. Homework
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12. The Wave Nature of Light (cont.)
Sunlight contains a continuous range of wavelengths and frequencies.
A prism separates sunlight into a continuous spectrum of colors.
The electromagnetic spectrum includes all forms of electromagnetic radiation.
Gamma rays, x-rays, radio waves, microwaves
Section 5-1

13. The Wave Nature of Light (cont.)
Section 5-1

14. The Particle Nature of Light
The wave model of light cannot explain all of light’s characteristics.
Matter can gain or lose energy only in small, specific amounts called quanta.
A quantum is the minimum amount of energy that can be gained or lost by an atom.
Planck’s constant has a value of  10–34 J ● s.
Section 5-1

15. Photoelectric Effect
An experiment designed to measure the energy carried by an electromagnetic wave
Shining light on alkali metals knocks electrons off
Brightness of light has NO EFFECT on the Kinetic Energy per electron
Brighter light simply ejects MORE electrons!
Red light can not eject electrons- Blue light can!
Photoelectric Effect

16. The Particle Nature of Light (cont.)
Albert Einstein proposed in 1905 that light has a dual nature.
A beam of light has wavelike and particlelike properties.
A photon is a particle of electromagnetic radiation with no mass that carries a quantum of energy.
Ephoton = h Ephoton represents energy. h is Planck's constant.  represents frequency.
Section 5-1

17. E = h * ν The energy per electron can be calculated.
frequency-to-energy conversion factor is “h” (Planck's constant, 6.626×10-34 J·s)
E = h * ν
ENERGY = Planck’s Constant * frequency
Planck’s Constant

18. energy (E ) of electromagnetic radiation is directly proportional to frequency () of radiation.
Planck-Einstein Equation: E = h
E = Energy, in units of Joules (kg·m2/s2)
(Joule is metric unit of energy)
h = Planck’s constant (6.626 x J·s)
(reflecting sizes of energy quanta)
 = frequency, in units of hertz (hz, sec-1)

19. Atomic Emission Spectra (cont.)
The atomic emission spectrum of an element is the set of frequencies of the electromagnetic waves emitted by the atoms of the element.
Each element’s atomic emission spectrum is unique.
Section 5-1

20. Atomic Emission Spectra
Light in a neon sign is produced when electricity is passed through a tube filled with neon gas and excites the neon atoms.
The excited atoms emit light to release energy.
Section 5-1

21. A B C D Section 5.1 Assessment
What is the smallest amount of energy that can be gained or lost by an atom?
A. electromagnetic photon
B. beta particle
C. quanta
D. wave-particle A B C D
Section 5-1

22. A B C D Section 5.1 Assessment
What is a particle of electromagnetic radiation with no mass called?
A. beta particle
B. alpha particle
C. quanta
D. photon A B C D
Section 5-1

23. A certain photon of light has a wavelength of 422 nm
A certain photon of light has a wavelength of 422 nm. What is the frequency of the light?
What is the energy of a quantum of light with a frequency of 7.39 x 1014 Hz?
A certain red light has a wavelength of 680 nm. What is the frequency of the light?
A certain blue light has a frequency of 6.91 x 1014 Hz. What is the wavelength of the light?
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Practice Problems: