Transcript Defining the Atom

Electrons in Atoms
5.3 Physics and the Quantum Mechanical Model
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
Light
How are the wavelength and frequency of light related?
i.
The amplitude of a wave is the wave’s height from zero to the
crest.
ii.
The wavelength, represented by  (the Greek letter lambda), is the
distance between the crests.
Light
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
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
How are the wavelength and frequency of light related?
v.
The wavelength and frequency of light are inversely
proportional to each other.
5.1
5.1
5.1
5.1
1. What is the frequency of radiation with a wavelength of 5.00 x 10-8 m?
Knowns
c = 2.998 x 108 m/s
λ = 5.00 x 10-8 m
c = λν therefore ν = c/λ
ν = 2.998 x 108 m/s = 6.00 x 1017 s-1
5.00 x 10-8 m
2. What is the wavelength of radiation with a frequency of of 5.00 x 1015 Hz?
Knowns
c = 2.998 x 108 m/s
ν = 5.00 x 1015 s-1
c = λν therefore λ = c/ν
λ = 2.998 x 108 m/s = 6.00 x 10-6 m
5.00 x 1015 m
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.
Remember  1nm = 1 x 10-9m (check on page 74 of text book for SI units)
Knowns
c = 2.998 x 108 m/s
λ = 650nm = 6.50 x 10-7 m
c = λν therefore ν = c/λ
ν = 2.998 x 108 m/s = 4.61 x 1014 s-1
6.50 x 10-7 m
5.3
Atomic Spectra
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
Atomic Spectra
Atomic Spectra
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.
5.3
An Explanation of Atomic Spectra
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
Quantum Mechanics
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’. (λ = 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.
5.3
Atomic Spectra
Quantum Mechanics
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.
The Heisenberg Uncertainty Principle
5.3 Section Quiz.
1. Calculate the frequency of a radar wave
with a wavelength of 125 mm.
a)
b)
c)
d)
2.40 109 Hz
2.40 1024 Hz
2.40 106 Hz
2.40 102 Hz
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.
5.3 Section Quiz.
3. Spectral lines in a series become closer
together as n increases because the
a)
b)
c)
d)
energy levels have similar values.
energy levels become farther apart.
atom is approaching ground state.
electrons are being emitted at a slower rate.
5.1 Vocabulary
2.3
Vocabulary
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Energy
levels: possible electron orbits in Bohr’s model of the atom
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Quantum: small whole number unit of energy
Quantum mechanical model: quantum description of the movement of electrons in atoms obtained
from solving Schrodinger’s equations
Atomic orbital: region of space where there is a high probability of finding an electron
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5.2 Vocabulary
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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.
5.4 Vocabulary
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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 can’t find the position and velocity of a particle simultaneously
END OF SHOW