Unit 3 – Electron Configurations
Part A – Electromagnetic Waves
River Dell Regional High School
What had we learned so far?
 Atomic Structure –
 Nucleus
 Electrons
 Essential question: how are those
electrons surrounding nucleus
arranged?
Experimental Evidence
Discharging Tubes
The Flame Test
The light coming out of the excited
atomic entities is very specific to
particular element!
Results are quite reproducible.
Experimental Evidence
There has been no
radioactive decay going on.
Hence the nucleus does not
change when the atomic
entity gets excited either by
electricity or heat.
So the colored light
must have come from
those electrons.
Light emitted from excited atomic entities is the tool
used to probe how electrons are arranged.
What is light?
Lights, both visible and invisible to human eyes,
are electromagnetic waves.
Time Out! Before
we go any further,
what is a Wave?
What is a wave?
A wave is a means to transfer energy from point A to point B.
Waves in water
Sound waves
Typical mechanical waves such as those in
water and sound waves DO need medium
in which they propagate. Water and air are
the prerequisites for waves to travel.
Waves – in more the abstract form
Wavelength - distance from crest to crest
abbreviated Greek letter, l, pronounced “lambda”. Also
can be defined as how far the wave travels in a cycle.
Note: great link to an online simulation of waves.
http://phet.colorado.edu/sims/wave-on-a-string/wave-on-a-string_en.html -
Waves – in more the abstract form
Frequency – the number of
complete waves passing any
given point per second.
• SI unit for frequency is
Hertz (Hz), or cycles/sec.
• Abbreviated Greek letter,
n, pronounced “nu”.
The graph shows that the top wave passes
any given point 4 complete wave forms
every second; the middle one 2 complete
wave forms; and the bottom one 1
complete wave form.
Waves – in more the abstract form
Wavelength - defined
as how far the wave
travels in a cycle.
Frequency – the number
of complete waves
passing any given point
per second.
Wavelength x Frequency =
how far the wave travels in a
second (speed of the wave)
s = ln
s: speed of wave
l: wavelength
n: frequency
Exercise I
Pause and complete the
following exercise before
proceeding.
1. What is the frequency of a wave in water where the speed of the wave is
3.4m/s and the wavelength is 0.5 m?
2. What is the speed of the sound wave where the wavelength is 4.5 m and
the frequency is 36 kHz. (1kHz = 103 Hz)
3. What is the wavelength of a sound wave that travels at 2300 m/s and at
a frequency of 150 Hz?
s = ln
s: speed of wave
l: wavelength
n: frequency
Exercise I
Answers to the Questions.
1. What is the frequency of a wave in water where the speed of the wave is
3.4m/s and the wavelength is 0.5 m? [6.8 Hz]
2. What is the speed of the sound wave where the wavelength is 4.5 m and
the frequency is 36 kHz. (1kHz = 103 Hz) [1.62 x 105 m/s]
3. What is the wavelength of a sound wave that travels at 2300 m/s and at
a frequency of 150 Hz? [15.3 m]
s = ln
s: speed of wave
l: wavelength
n: frequency
Electromagnetic Waves (Lights)
Disturbance in a magnetic
field is perpendicular to a
disturbance in an electric
field.
• Can travel in vacuum. No need for medium!
• Travels at 3 x1010 cm/second (or 3.00 x 108 m/s)in vacuum. Known as
the “Speed of Light”, which does not vary with frequency nor
wavelength
• Varying in wavelength and frequency.
Electromagnetic Waves (Lights)
Since the speed of light in vacuum does not change with
frequency nor wavelength, frequency and wavelength are
inversely proportional.
c = ln
c: speed of light (3.00 x 108 m/s)
l: wavelength
n: frequency
• For an electromagnetic wave, frequency goes up, then wavelength has
to come down proportionally and vies versa.
Electromagnetic Waves (Lights)
Now you have all the parameters and two relationships
(see boxes below). Then you should be able to solve
problems related to lights. Keep in mind how to
manipulate parameters and variables. Good luck!
c = ln
E = hn
c: speed of light (3.00 x 108 m/s)
E: energy of the photon
h: Planck’s constant, 6.626 x 10-34 J.s
l: wavelength
n: frequency
n: frequency
http://www.colorado.edu/physics/2000/quantumz
one/photoelectric2.html
Exercise II – Electromagnetic Waves
c = ln
c: speed of light (3.00 x 108 m/s)
l: wavelength
n: frequency
E = hn
E: energy of the photon
h: Planck’s constant, 6.626 x 10-34 J.s
n: frequency
1. What is the frequency of an electromagnetic wave with wavelength of
3.4m?
2. What is the wavelength of the light where the frequency is 36 MHz.
(1MHz = 106 Hz)
3. What is the energy of a photon that has a frequency of 4.23 x 107 Hz?
4. What is the wavelength of a photon that carries 2.56 eV energy? (1
eV=1.602 x 10-19 J)
Exercise II – Electromagnetic Waves
Answers
1. What is the frequency of an electromagnetic wave with wavelength of
3.4m? [8.82 x 107 m/s]
2. What is the wavelength of the light where the frequency is 36 MHz.
(1MHz = 106 Hz) [8.33 m]
3. What is the energy of a photon that has a frequency of 4.23 x 107 Hz?
[2.80 x 10-26 J]
4. What is the wavelength of a photon that carries 2.56 eV energy? (1
eV=1.602 x 10-19 J) [4.85 x 10-7 m]
Exercise II – Electromagnetic Waves
c = ln
c: speed of light (3.00 x 108 m/s)
l: wavelength
n: frequency
E = hn
E: energy of the photon
h: Planck’s constant, 6.626 x 10-34 J.s
n: frequency
2. What is the energy of a photon that has a frequency of 4.23 x 107 Hz?
3. What is the wavelength of a photon that carries 2.56 eV energy? (1
eV=1.602 x 10-19 J)
Electromagnetic Waves (Radiations)
Examples:
 radio waves
 microwaves
 infrared
 white light (visible spectrum)
 ultraviolet light
 X-rays
 gamma radiation
High
Energy
Low
Energy
Radio Micro Infrared
waves waves .
Ultra- XGamma
violet Rays Rays
Low
Frequency
Long
Wavelength
Visible Light
High
Frequency
Short
Wavelength
---------------- > decreasing energy ---------------------
----------------> decreasing frequency ---------------->
---------------> increasing wavelength ---------------->
Diagram Showing Wavelength and Frequency
Types of Spectra
 Continuous – all wavelengths within a given
range are included.
 Electromagnetic – all electromagnetic radiation
arranged according to increasing or decreasing
wavelength.
a. unit for wavelength ranges from meters to
nanometers
b. unit for frequency is hertz (Hz) (# waves per
second)
Types of Spectra
 Visible spectrum - light you can see (ROY-G-BIV)
a. Red has the longest wavelength and the smallest
frequency.
b. Violet has the shortest wavelength and the greatest
frequency.
 Bright Line spectrum (emission spectrum)
 Bands of colored light emitted by excited electrons
when they return to the ground state.
Passing Light Through a Prism
 White light is made
up of all the colors
of the visible
spectrum.
 Passing it through a
prism separates the
colors in white light.
If the light is not white,
 By heating a gas with
electricity we can
get it to give off
colors.
 Passing this light
through a prism
does something
different.
If the light is not white,
 Each element gives
off its own
characteristic colors.
 Can be used to
identify the atom.
 This is how we know
what stars are made
of.
Spectroscopy
1. Emission spectra of a substance is studied to
determine its identity.
2. Spectroscope – instrument that separates light
into a spectrum.
3. Spectral lines – represent wavelength of light
emitted when excited electrons fall back to the
ground state.
How Does a Spectroscope Work?
Emission Spectrum (Line Spectrum)
Emission Spectrum