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Chapter 6: Starlight and Atoms
Properties of Matter
• _______ of matter
• ______ of matter
• How _______ is stored in atoms
How do light and matter interact?
To study the largest objects in the universe, we must
first understand the smallest objects in the universe!
What is the structure of
matter?
•
•
Electron
Cloud
Atom
Atomic Terminology
Atomic Number = # of ______ in nucleus
Atomic Mass Number = # of _______ + __________
Nucleus
• Molecules: consist of two or more _____ (H2O, CO2 )
Atomic Terminology
• Isotope: same # of protons but different # of
________. (4 He, 3He)
What are the phases of matter?
• Familiar phases:
– Solid (ice)
– Liquid (water)
– Gas (water vapor)
• Phases of same material behave
differently because of differences in
_________ _______
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Phase Changes
• ________: Breaking of rigid
chemical bonds, changing
solid into liquid
• ____________: Breaking of
flexible chemical bonds,
changing liquid into gas
• ____________: Breaking of
molecules into atoms
• __________: Stripping of
electrons, changing atoms into
plasma
How is energy stored in atoms?
• Electrons in atoms are restricted to
particular _______ _____ (electron shells)
Energy Level Transitions
• An electron
can only go
from one
level to
another, not
in between
___ ________
A Simple Atom
• Only 2 energy levels
– Ground (E1)
– Excited (E2)
• Right now electron is
at E1
________
A Simple Atom
• Excitation
– Electron ______ a
photon and jumps
from E1 to E2
– Photon only
absorbed if it has
energy = (E2-E1)
A Simple Atom
• Ionization
– Electron ______ a
photon and leaves!
– Only works if electron
is in higher energy
levels
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A Simple Atom
• De-excitation
– Electron _____ a
photon of energy
(E2-E1)
– Electrons like to be in
the ground state
What are the three basic types
of spectra?
________ Spectrum
__________ Spectrum
__________ Spectrum
Spectra of astrophysical objects are usually
combinations of these three basic types
_________ Spectrum
• All wavelengths, no breaks
• Rainbows!
__________ Spectrum
_________ Spectrum
• Bright, individual lines
• Also called ______-____ spectrum
• Electrons are moving to lower energy levels,
emitting photons of light
Kirchhoff’s Laws
I.
• Rainbow with dark lines on top
• Also called ____-____ spectrum
• Atoms in the cloud are absorbing photons, moving to
higher energy levels
A hot, dense substance will give off
____________ spectrum
II. A hot, low-density gas will give off an
__________ spectrum
III. A cool, low-density gas in front of a
continuous-spectrum source will give
off an ___________ spectrum
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Chemical Fingerprints
• Each type of
atom has a
unique set of
energy levels
Energy levels of Hydrogen
• Each transition
corresponds to a
unique photon
energy,
frequency, and
wavelength
Chemical Fingerprints
• Each type of atom has a unique spectral
fingerprint, due to ________ of ______ _____
Energy Levels of Molecules
Spectrum of Molecular Hydrogen (H2)
• Spectra of molecules can be very complicated
– Lots of energy modes
• Molecular transitions are typically in the IR
Chemical Fingerprints
• Downward
transitions
produce _______
lines
• Upward
transitions
produce
__________ lines
Energy Levels of Molecules
• Molecules have additional energy levels
because they can vibrate and rotate
Light and Atoms Lecture
Tutorial: page 63
• Work with a partner or two
• Read directions and answer all questions carefully.
Take time to understand it now!
• Come to a consensus answer you all agree on before
moving on to the next question.
• If you get stuck, ask another group for help.
• If you get really stuck, raise your hand and I will
come around.
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What can we learn from light?
•
•
•
•
Temperature
Energy
Chemical Composition
Speed towards or away from us
• Why do different objects give off
different forms of light?
• They have different ___________!
– Temperature depends on the motion of
_____ & __________
– Fast motion -> High temp.
– Slow motion -> Low temp.
All from the spectrum!
Temperature, Heat, or
Thermal Energy?
Kelvin Temperature Scale
• Temperature: ________ of thermal
energy
• Heat: ______ of thermal energy
Two objects can be at the same
temperature, but have different amounts
of heat or thermal energy
Temperature and Color
• Higher temp = higher E= higher f = shorter λ
• What color has shorter wavelength?
– _________
– Opposite of faucet handles…
400 nm
Temperature and Radiation
• Zero Kelvin (written 0 K) is absolute
zero (-459.7ºF)
– No heat energy
• Water freezes at 273 K, boils at 373 K.
K = ºC + 273.2
Spectrum: Wavelength vs.
Intensity
• Visible:
• Intensity vs. wavelength plot:
700 nm
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They show the same information
“Dips” in _____ = black lines
Temp. and Color: Blackbodies
• A blackbody absorbs and re-emits all
light that falls on it
• Idealized objects
– But still a good model for ______
• They don’t actually look black
(misnomer)
– Color depends on their temperature
Dips in ________
Radiation from a
Heated Object
• Intensity vs. wavelength
for three objects of
different temperatures.
Radiation from a
Heated Object
• The total ____ under
each curve is
proportional to the total
_______ emitted.
– Hotter object emits more
total energy than cooler
objects.
Radiation from a
Heated Object
• The curves are high in
the middle and low at
either end.
– These objects emit most
intensely at middle
wavelengths.
Radiation from a
Heated Object
• Wavelength of
maximum intensity
depends on
__________.
– The _____ the object, the
________ the wavelength of
max. intensity
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Radiation from a
Heated Object
Temp. and Color: Blackbodies
______ Object
• Temperature determines
the _____ of a glowing
black body.
– The hotter object emits more
____ light than ____, and thus
looks ____.
– The cooler object emits more
____ than ____, and
consequently looks ____.
Blackbody Radiation Lecture
Tutorial: page 57
• Work with a partner or two
• Read directions and answer all questions carefully.
Take time to understand it now!
• Come to a consensus answer you all agree on before
moving on to the next question.
• If you get stuck, ask another group for help.
• If you get really stuck, raise your hand and I will
come around.
_______ Object
Comparing Spectra
• Peak at shorter wavelength = _______
temperature
• Higher temperature = _____ in color
• Larger _____ ____ under curve =
higher total ______ ______
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Example: Solar Spectrum
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