In This Lesson:
Atomic Emissions
(Lesson 2 of 4)
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Today is Tuesday,
September 29th, 2015
Pre-Class: [choose one]
What is white light?
How are fireworks made to be different
colors?
How are neon signs made to be
different colors?
Today’s Agenda
•
•
•
•
Atomic Emissions
Flame Tests
The Light Spectrum
Calculations
• Where is this in my book?
– P. 138 and following…
By the end of this lesson…
• You should be able to explain what happens
when energy is applied to an atom.
• You should be able to describe and calculate
the relationships between wavelength,
frequency, and energy.
Emission Spectra
• Fireworks are
exciting because of:
– The noise they make.
– The variety of color
they display.
• We’re going to focus
on the color.
Identification
• The multicolored lights
created by fireworks
occur because of the
different elements that
comprise the powder in
fireworks.
• Fireworks Filmed with a
Drone video
Identification
• Scientists have found
that each element,
when heated, gives off
its own specific set of
colors.
• The element’s colors
are its “fingerprints”
and can be used to
identify the element.
Element Colors
Element
Sodium
Potassium
Rubidium
Calcium
Strontium
Barium
Copper
Flame Color
Yellow
Violet
Pinkish-Red
Orange-Red
Red
Green
Blue-Green
Cesium
• Blue
Calcium
• Deep Orange
Sodium
• Orange
Potassium
• Violet
Copper
• Jade Green
Flame Tests
Many elements give off characteristic light which can
be used to help identify them.
Strontium
Sodium
Lithium
Potassium
Copper
Electron Energy State
• Electrons absorb energy from the
flame.
• When a certain amount is reached (a
quantum), they jump to a higher
energy level: the “excited state.”
• Eventually, the electrons lose the
energy in the form of light and fall
back to the lowest, most stable energy
level: the “ground state.”
Atomic Emission Spectrum of Barium using a Spectrometer
Electromagnetic Spectrum
Lyman, Balmer, Paschen Series
• Electrons moving down to n=1
emit light along a series of
frequencies in the ultraviolet
range.
– The Lyman series of emissions.
• Electrons moving down to n=2
emit light along a series of
frequencies in the visible range.
– The Balmer series of emissions.
• Electrons moving down to n=3
emit light along a series of
frequencies in the infrared
range.
– The Paschen series of emissions.
http://1.bp.blogspot.com/_nxSb3loAy3A/TGedfwHgN8I/AAAAAAAAAN8/JhEss5aeCE8/s1600/h-atom.gif
Lyman, Balmer, Paschen Series
Sources of Energy
• Where do electrons get energy to “jump” to
the next higher energy level?
– Collisions from other particles
– Heat
– Electricity
– Light
Loss of Light?
• As we learned, when electrons fall back to the
ground state, they release energy in the form of
light.
• It’s complicated, but light can behave as a wave
or a particle.
• As a particle, a “unit” of light is called a photon.
– Additionally, a quantum (plural: quanta) is the amount
of energy needed to move an electron into an excited
state.
– A quantum of light is called a photon.
Particle-Wave Duality
Wave Statistics
• Amplitude: The “height” of the wave from zero
to crest (peak).
• Wavelength: Distance between peaks in
nanometers (nm) or meters (m).
– Given by Greek letter λ (lambda).
• Frequency: The number of cycles (wave peaks)
that occur in a unit of time (per second or Hertz;
Hz).
– Given by Greek letter v (nu).
Wave Equation
• There is a relationship between wavelength
and frequency.
• Wavelength times frequency always equals
the speed of light, given by c and equal to
2.998 x 108 m/s.
• c = λv
• Sample Problem:
– Wave Statistics Worksheet: #9
Wavelength, Frequency, and Energy
Long
Wavelength
=
Low Frequency
=
Low Energy
Short
Wavelength
=
High Frequency
=
High Energy
How to remember?
• How can you remember “high frequency =
high energy?”
• Imagine riding a bike over the wave peaks!
Takes less energy to do
these hills…
…than to do these hills.
-Litz, 2014
Planck’s Constant
• In addition to the speed of light
constant c, there is also Planck’s
Constant, named for the particularly
dour-looking Max Planck.
• Planck’s Constant, given by h, relates
the energy of one photon and the
frequency of the corresponding
wave.
• Energy (E) is in joules (J).
• E = hν
(for one photon)
• h = 6.626 x 10-34 Js
• Sample Problem:
– Wave Statistics Worksheet: #1
http://adam.humanisti.sk/wp-content/2007/10/max_planck.jpg
Max Planck
Summary
• Electrons can move between energy levels.
– Ground state: stable state; an electron is at the
lowest energy level.
– Excited state: unstable state; an electron is at a
higher energy level.
– Quantum: the amount of energy needed to move
an electron from the ground to excited state.
– Photon: a quantum of light.
Summary
• Wavelength and frequency are inversely
related:
– When wavelength increases, frequency decreases.
• Frequency and energy are directly related:
– When frequency increases, energy increases.
• We only see a small part of all possible
wavelengths/frequencies.
– The visible spectrum.
Summary
• Variables:
• λ (lambda) – measure of wavelength.
• v (nu) – measure of frequency in Hz (cycles/sec).
• c – speed of electromagnetic waves.
• 2.998 x 108 m/s in a vacuum.
• h – Planck’s Constant.
• 6.626 x 10-34 Js
• Equations:
• c = λv
• E = hv
Heads Up!
For the quiz on this material,
you’ll be provided both the
constants and equations.
For the test on this material,
you’ll just get the constants.
Other Equations?
• Related equations not covered directly in this
course:
• E=mc2
• Energy = mass * speed of light 2
• De Broglie’s Equation: λ = h/mv
• Allows us to relate Planck’s Constant, mass, and velocity
to wavelength.
– Also illustrates the particle-wave duality of matter.
Summary: Emissions in Real Life
• The reason most streetlights look a little
“orange” is because they pass an electric
current through sodium vapor.
– Remember how sodium burns in orange color?
• Compare LED light to Na vapor:
http://ledlightreviews.files.wordpress.com/2009/08/led-vs-hps-betaled1.jpg?w=460&h=179
So now then…
• Let’s try some flame tests!
• At each of your lab tables is one of seven
different kinds of salt solutions.
– This isn’t table salt.
• In the salt solution is a wooden splint that has
been soaking in it overnight.
• You should take out your Bunsen burner (if it’s
not already out) and light it.
Flame Tests
• I will turn off the lights.
• At that point, each group will put ONE of the
splints into the flame and record the color
that is emitted.
• The lights will come back on, and groups will
rotate clockwise until all solutions have been
tested.
• There will be time for answering the questions
that follow.
What NOT to do…
• Don’t let the splint burn.
• Don’t place more than one splint into the
flame.
Closure
• Which has higher energy, long or short wavelength?
– Short wavelength (high frequency).
• Exactly what is burning?
– The various salt solutions (NOT the splint)
• Did the electrons get closer to the nucleus or further
away?
– Further
• What could we say happened to the electrons in terms
of their Principal Quantum Number?
– They briefly entered a higher energy shell (or principal
quantum number) before falling back into their ground
levels.