Electrons in Atoms 5.3 Physics and the Quantum Mechanical
Model
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Chemistry Today we are learning to:- 1. Understand the
relationship between the wavelength and frequency of light 2.
Understand the reasons for emission spectra 3. Explain how
frequencies of emitted light are related to changes in electron
energy 4. Distinguish between quantum mechanics and classical
mechanics
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How are the wavelength and frequency of light related? i.The
amplitude of a wave is the waves height from zero to the crest.
ii.The wavelength, represented by (the Greek letter lambda), is the
distance between the crests. Light
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How are the wavelength and frequency of light related? iii.The
frequency, represented by (the Greek letter nu), is the number of
wave cycles to pass a given point per unit of time. iv.The SI unit
of cycles per second is called a hertz (Hz). Light
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How are the wavelength and frequency of light related? iv.The
product of the frequency and wavelength always equals a constant
(c), the speed of light. Light
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How are the wavelength and frequency of light related? v.The
wavelength and frequency of light are inversely proportional to
each other. Light
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5.1
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1.What is the frequency of radiation with a wavelength of 5.00
x 10 -8 m? 2.What is the wavelength of radiation with a frequency
of of 5.00 x 10 15 Hz? Knowns c = 2.998 x 10 8 m/s = 5.00 x 10 -8 m
c = therefore = c/ = 2.998 x 10 8 m/s = 6.00 x 10 17 s -1 5.00 x 10
-8 m Knowns c = 2.998 x 10 8 m/s = 5.00 x 10 15 s -1 c = therefore
= c/ = 2.998 x 10 8 m/s = 6.00 x 10 -6 m 5.00 x 10 15 m
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for Sample Problem 5.1 3.An inexpensive laser that is available
to the public emits light that has a wavelength of 650nm. What is
the frequency of the radiation. Knowns c = 2.998 x 10 8 m/s = 650nm
= 6.50 x 10 -7 m c = therefore = c/ = 2.998 x 10 8 m/s = 4.61 x 10
14 s -1 6.50 x 10 -7 m Remember 1nm = 1 x 10 -9 m (check on page 74
of text book for SI units)
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Atomic Spectra When light from a helium lamp passes through a
prism, discrete lines are produced The frequencies of light emitted
by an element separate into discrete lines to give the atomic
emission spectrum of the element. 5.3
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Atomic Spectra 5.3 In the Bohr model: When the electron has its
lowest possible energy, the atom is in its ground state. Excitation
of the electron by absorbing energy raises the atom from the ground
state to an excited state. A quantum of energy in the form of light
is emitted when the electron drops back to a lower energy
level.
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An Explanation of Atomic Spectra The three groups of lines in
the hydrogen spectrum correspond to the transition of electrons
from higher energy levels to lower energy levels. 5.3 Atomic
Spectra
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Quantum Mechanics 5.3 Main points: (1905 Special Relativity
Theory) Einstein showed that light could be described by packets of
energy (quanta) called photons. (1924) DeBroglie developed an
equation that predicts that all moving particles have wavelike
behavior (Ex. electrons). This is called the wave particle duality
of matter. ( = h/p = h/mv) The wavelike properties of electrons are
used in electron microscopes They have much smaller wavelengths
than visible light, and can give greater magnification.
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Atomic Spectra Quantum Mechanics 5.3 Main points: Classical
mechanics describes the motions of bodies much larger than atoms,
while quantum mechanics describes the motions of subatomic
particles and atoms as waves. The Heisenberg uncertainty principle
states that it is impossible to know exactly both the velocity and
the position of a particle at the same time.
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The Heisenberg Uncertainty Principle
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5.3 Section Quiz. 1.Calculate the frequency of a radar wave
with a wavelength of 125 mm. a)2.40 10 9 Hz b)2.40 10 24 Hz c)2.40
10 6 Hz d)2.40 10 2 Hz
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5.3 Section Quiz. 2.The lines in the emission spectrum for an
element are caused by a)the movement of electrons from lower to
higher energy levels. b)the movement of electrons from higher to
lower energy levels. c)the electron configuration in the ground
state. d)the electron configuration of an atom.
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5.3 Section Quiz. 3.Spectral lines in a series become closer
together as n increases because the a)energy levels have similar
values. b)energy levels become farther apart. c)atom is approaching
ground state. d)electrons are being emitted at a slower rate.
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2.3 Vocabulary 5.4 Vocabulary Amplitude: waves height from the
origin. Wavelength: distance between crests. Frequency: number of
waves passing a given point per second. Hertz: S.I. Unit of
frequency 1 Hz = 1s -1 = 1 1/s = 1 cycle per second.
Electromagnetic radiation: Radiation over a broad band of
wavelengths. Spectrum: The result of light being split into its
component colors. Atomic emission spectrum: Spectrum from the light
emitted by an element. Ground state: Lowest energy state of an
electron in an atom. Photons: Quanta of light particles Heizenberg
uncertainty principle: You cant find the position and velocity of a
particle simultaneously 5.2 Vocabulary Electron configuration:
knocks electrons of atoms to produce ions Aufbau principle:
Electrons occupy orbitals of lowest energy first. Pauli exclusion
principle: Atomic orbitals can hold up to 2 electrons of opposite
spin. Hunds rule: All orbitals of the same energy must have an
electron in them before they can pair up. 5.1 Vocabulary Energy
levels: possible electron orbits in Bohrs model of the atom
Quantum: small whole number unit of energy Quantum mechanical
model: quantum description of the movement of electrons in atoms
obtained from solving Schrodingers equations Atomic orbital: region
of space where there is a high probability of finding an
electron