Section 5.1 Light and Quantized Energy

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Section 5-1
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.

radiation the rays and particles alpha
particles, beta particles, and gamma raysthat
are emitted by radioactive material
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Section 5-1
Section 5.1 Light and Quantized Energy (cont.)
electromagnetic radiation wavelength frequency amp
litude electromagnetic spectrum
quantum Planck's constant photoelectric
effect photon atomic emission spectrum
Light, a form of electronic radiation, has
characteristics of both a wave and a particle.
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Section 5-1
The Atom and Unanswered Questions

• Recall that in Rutherford's model, the atoms
  mass is concentrated in the nucleus and electrons
  move around it.

• The model doesnt explain how the electrons were
  arranged around the nucleus.
• The model doesnt explain why negatively charged
  electrons arent pulled into the positively
  charged nucleus.

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Section 5-1
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
  elements chemical behavior is related to the
  arrangement of the electrons in its atoms.

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Section 5-1
The Wave Nature of Light

• Visible light is a type of electromagnetic
  radiation, a form of energy that exhibits
  wave-like behavior as it travels through space.

• All waves can be described by several
  characteristics.

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

• The wavelength (?) is the shortest distance
  between equivalent points on a continuous wave.

• The frequency (f) is the number of waves that
  pass a given point per second. The unit for
  frequency is 1/sec or sec-1, which is known as a
  Hertz.
• The amplitude is the waves height from the
  origin to a crest.

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

• The speed of light (3.00 ? 108 m/s) is the
  product of its wavelength and frequency c ?f.

c ?f
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EM Spectrum

• EX Find the frequency of a photon with a
  wavelength of 434 nm.

GIVEN f ? ? 434 nm 4.34 ? 10-7 m c
3.00 ? 108m/s
f 6.91 ? 1014 Hz
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Section 5-1
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.

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

• The wave model of light cannot explain all of
  lights characteristics.

• Matter can gain or lose energy only in small,
  specific amounts called quanta.
• Max Planck (1900) Observed - emission of light
  from hot objects
• Concluded - energy is emitted in small, specific
  amounts (quanta)
• A quantum is the minimum amount of energy that
  can be gained or lost by an atom.
• Plancks constant has a value of 6.626 ? 1034 J
  ? s.

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

• The photoelectric effect is when electrons are
  emitted from a metals surface when light of a
  certain frequency shines on it.

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

• Albert Einstein proposed in 1905 that light has a
  dual nature.

• A beam of light has wavelike and particle like
  properties.
• A photon is a particle of electromagnetic
  radiation with no mass that carries a quantum of
  energy.

E hf
Ephoton hf Ephoton represents energy. h is
Planck's constant. f represents frequency.
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Quantum Theory

• EX Find the energy of a red photon with a
  frequency of 4.57 ? 1014 Hz.

GIVEN E ? f 4.57 ? 1014 Hz h 6.6262 ?
10-34 Js
WORK E hf E (6.6262 ? 10-34 Js)(4.57 ? 1014
Hz) E 3.03 ? 10-19 J
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Section 5-1
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.

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Section 5-1
Atomic Emission Spectra (cont.)
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Section 5-1
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 elements atomic emission spectrum is
  unique. Like a finger print.

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Section 5-1
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

1. A
2. B
3. C
4. D

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Section 5-1
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

1. A
2. B
3. C
4. D