Download Review Worksheet Solutions

• Chapter 3 Review Worksheet
1. Describe the plasma phase of matter.
Under what conditions is matter a
plasma?
• A plasma is a hot gas
made of charged
atoms, called ions.
Atoms become
charged when they
are stripped of
electrons in a process
called ionization. This
happens at very high
temperatures.
2. Describe the difference between
transparent and opaque materials.
• A transparent object
allows light to pass
through it or transmits
light. The plastic bag
is transparent to
infrared light.
• An opaque object
absorbs light. The
plastic bag is opaque
to visible light.
3. Why do objects appear to have a certain
color?
• Interactions between
light and matter
determine the
appearance of
everything around us.
• Objects appear a certain
color based on the colors of
light they reflect!
4. Describe the major regions of the
electromagnetic spectrum in terms of
wavelength, frequency and energy.
5. How is the wavelength related to the
frequency?
6. Describe the characteristics of
continuous, emission, and absorption
spectra and the conditions under which
each is produced.
Continuous Spectrum
• An unbroken band of colors produced by
glowing solids, liquids & high pressure gases.
• Ex: The spectrum of a common
(incandescent) light bulb spans all visible
wavelengths, without interruption
Emission Line Spectrum
• Produced by hot gases under low pressure.
• EX: A thin or low-density cloud of gas emits light only
at specific wavelengths that depend on its
composition and temperature, producing a spectrum
with bright emission lines
Absorption Line Spectrum
• Produced when a continuous spectrum of light is
passed through a cooler, low pressure gas.
• EX: A cloud of gas between us and a light bulb can
absorb light of specific wavelengths, leaving dark
absorption lines in the spectrum
7. Briefly describe the structure of an atom.
• Nucleus- contains
protons & neutrons
• Electron cloudcontains electrons
• electrons are
arranged in energy
levels in the cloud
8. What is electrical charge? Will an
electron and a proton attract or repel
each other?
• Electric charge is a property of protons
(+) and electrons (-). They attract each
other. This is what holds an atom
together.
9. The most common
form of iron has 26
protons and 30
neutrons. State its
atomic number,
atomic mass
number, and number
of electrons if it is
electrically neutral.
• Atomic number = 26
• Mass number = 56
• Electrons = 26
10.Consider the
following three
atoms: atom 1 has 7
protons and 8
neutrons; atom 2
has 8 protons and 7
neutrons; atom 3
has 8 protons and 8
neutrons. Which two
are isotopes of the
same element?
• Isotopes have the
same number of
protons. Atoms 2 and
3 are isotopes.
11.Explain how electron transitions within
atoms produce unique emission and
absorption spectra.
11.Explain how electron transitions within atoms
produce unique emission and absorption spectra.
Not Allowed
Allowed
• Electrons gain
energy (by
absorbing light) and
jump to a higher
level
• Electrons lose
energy ( by emitting
light) and drop to a
lower level
• The only allowed
energy changes are
those corresponding
to a transition
between levels
11.Explain how electron transitions within atoms
produce unique emission and absorption spectra.
• Each transition
corresponds to a
unique photon
energy,
frequency, and
wavelength
Energy levels of Hydrogen
11.Explain how electron transitions within atoms
produce unique emission and absorption spectra.
• Downward
transitions
produce a unique
pattern of
emission lines
11.Explain how electron transitions within atoms
produce unique emission and absorption spectra.
• upward
transitions
produce a
pattern of
absorption
lines at the
same
wavelengths
11.Explain how electron transitions within atoms
produce unique emission and absorption spectra.
• Each type of atom has a unique spectral
fingerprint
• Observing the fingerprints in a spectrum tells
us which kinds of atoms are present
12.The following labeled transitions represent an
electron moving between energy levels in
hydrogen. a. Which transition, as shown, is not
possible?
Transition 3 isn’t possible
because it only goes halfway
from level 2 to level 3
b. what is the wavelength of light associated with
transition 5? Is the photon being absorbed or
emitted?
E1  10.2eV and E2  12.8ev
The energy difference is E2  2.6ev
This is the energy of the photon.
E photon 

hc

hc
E photon



8 m
4.14 x10 eVs  3 x10

s 


 4.78 x10  7 m
2.6eV
or 478 nm.
15
13.How can we use emission or absorption lines to
determine the chemical composition of a distant
object?
We compare the spectrum of the object to
known spectra. Each element has a unique
internal structure. Therefore, when an
electron moves from one energy level to
another in an atom of a given element it
involves a photon of light at a wavelength
that’s unique for that element. If this spectral
line is observed then, we know it must have
been produced by that element.
14.Describe two ways in which the thermal
radiation spectrum of an 8,000 K star would
differ from that of a 4,000 K star.
• The peak wavelength
for the hotter star will
be shorter (shifted
more to the UV end of
the spectrum. The
curve will also be
taller showing that it
emits more light at all
wavelengths than the
cooler star.
15.Suppose the surface temperature of the Sun
were about 12,000 K, rather than 6,000 K.
a) How much more thermal radiation would the
sun emit?
P T
4
4
 12,000 
4
so the increase in energy  

2
 16

 6,000 
b) What would happen to the Sun’s peak
wavelength?
• If the sun’s temperature doubled it’s peak
wavelength would decrease. The current peak is
at about 450 nm which is in the visible portion of
the spectrum. The new peak would be in the uv
portion of the spectrum .
2,900,000
p 
 242 nm
12,000
16.Describe the Doppler Effect for light and what
we can learn from it.
• The Doppler effect is the
change in wavelength of
light caused by motion
between the source and
the observer.
• If the source is moving
toward the observer the
light is blueshifted
• If the source is moving
away from the observer
the light is redshifted