Chapter 5
5A: Inside the Atom
Key Question: What is inside an atom?
In this Investigation, students explore the inner workings of atoms, which are often
known as the smallest building blocks of matter. While it is true that they cannot be
chemically split, here they learn that there are smaller particles that make up atoms. The
students also learn how many protons, electrons and neutrons are inside each atom, and
use the model to discover how to figure out the number of each in a given atom.
Reading Summary
Questions and goals
Students read section 5.1 (The Atom has a
Structure) before performing the investigation.
Main • What particles are found in atoms, and where?
Questions • How can you determine the number of protons, neutrons and electrons in an
All matter is made of atoms of the 92 naturally
occurring elements. These atoms usually form
compounds, such as salt (NaCl) or sodium bicarbonate
(NaHCO3). Compounds explain how we get millions
of types of matter from 92 elements, but 92 is still a
relatively large number. Are the 92 different types of
atoms (i.e. the elements) made of even smaller things?
The answer is: yes. Atoms are made from smaller
particles called protons, neutrons and electrons
This is an extraordinary fact! How can the incredible
variety of matter in the universe come from only three
particles? Think about making all the words in the
dictionary with only 3 letters, or all the paintings in
the world with only three colors. It may seem
incredible, but it is true nonetheless. The atoms of all
92 elements (and more) are created from three basic
particles: electrons, protons and neutrons. The
beautiful variety of nature arises from how the three
particles come together in rich and complex ways.
156
atom by looking at its mass and atomic number?
• What particles distinguish one atom from another?
• What particles distinguish one isotope from another?
Learning By the end of the Investigation, students will be able to:
Goals • Know the subatomic particles, and recite their locations in the atom.
• Determine the number of protons and neutrons in an atom, when given the
atomic mass and atomic number
• Say what makes one atom different from another, and what makes an isotope
different from another.
Key Vocabulary Proton, neutron, electron, nucleus, mass number, atomic number, isotope,
Chapter 5: The Structure of the Atom
atomic mass unit (amu), ion.
Materials and Setup
Each group should have:
• One atom model, complete with plastic particle holder, and
marbles representing all three types of particles.
Preparation
You will need to prepare one Atom Model station for each lab
group. Have the model front & center, and place a cup or tray of
proton, electron and neutron marbles at each station.
Hints:
• Separating the three types of marbles will make the lab go more
quickly for the students.
• Have some extra marbles on hand in case some are lost.
Teaching Time One class period
Preparation
Prepare one Atom Model station for each lab group.
Have the model front & center, and place a cup or
tray of proton, electron and neutron marbles at each
station.
Assignments Section 5.1 (The Atom has a Structure) in the
Student Text before the Investigation.
Misconceptions Students use the periodic table early on, and because
they do not yet understand isotopes they think that
there can be "parts" of neutrons and protons, due to
the fact that the mass number contains a decimal.
Inside the Atom
Students work in groups of two or three at tables.
5A
Details
Teaching the Investigation
1
2
3
4
Setting Up
Thinking about the atom
Atom Building
The average atomic mass
157
Investigation sections
Setting Up
Part
1
The Atom Model represents the particles inside an atom and how they are arranged.
The electron shells are on the left side of the model. The right side contains the nucleus. Make sure to
explain to the students that the electrons are ordered in shells, while the protons and neutrons are all just
close-packed inside the nucleus without any shells. Mention that the nucleus is very, very small compared to the electron shells.
Find the element lithium (Li) on the periodic table.
Lithium is in the upper left corner of the periodic table, just below hydrogen (H). Point out that many
atoms’ atomic symbols are just the first one or two letters of their name.
Use the colored marbles to build a lithium atom.
Students should end up with a nucleus with three protons, because the atomic number is 3. The mass
number is 7, so there should be 7-3=4 neutrons. Because it is a neutral atom, the number of electrons
should equal the number of protons (3).
2
What is the number of protons or electrons called?
The number of protons or electrons is called the atomic number. The number of protons, electrons and
the atomic number are all equal in a neutral (non-ionic) atom. This is a good fact for the students to
remember.
In the lithium atom, what are the numbers 6 and 7 called?
The numbers 6 and 7 are called the mass numbers. They represent the total number of nucleons (protons and neutrons) in the nucleus. To find the number of neutrons, subtract the atomic number from the
mass number.
Why do some elements have more than one number above the symbol? What are the variations in this number called?
The different mass numbers represent different isotopes of the same atom. Atoms with more than one
mass number have more than one isotope.
Confirm that all the students have a
complete atom model ready. Explain
the locations on the model for the
nucleus, and the electron shells. Also
explain that the nucleus is zoomed in,
and the representations for each type of
marble.
Thinking about the atom
The students should be able to answer
these questions, either from memory or
with the book in front of them.
158
Ideas and Dialog
Chapter 5: The Structure of the Atom
Investigation page
Sample answers
Example Answers
2a. The number of protons (and the number of electrons in a neutral atom) is called the
atomic number.
2b. The numbers 6 and 7 in the lithium atom are called the mass numbers.
2c. Some elements have more than one number above the symbol because they have
multiple isotopes. That means there are types of this atom with different atomic
masses.
Teaching Tips
It may help if you all build one atom with the students together, to show them how to
build atoms quickly. Take an atom from the 2nd or 3rd row, so it doesn’t take too long.
First, say that the atomic number is the number of protons as well as electrons, and fill in
the marbles together. Then say that the atomic mass minus the atomic number gives the
number of neutrons, and fill in those marbles together.
5 A: Inside the Atom
159
Investigation sections
Atom building
Part
3
Using the atom model, build the following elements: He, C, O. What do you notice about the number of
protons and neutrons?
The number of protons and neutrons should be equal. This is very common for elements with a low
atomic number.
Now build the following elements: Na, Al, P. What do you notice about the number of protons and neutrons?
There should be one more neutrons than protons. As atoms get heavier, they tend to pick up more neutrons compared to protons.
Now build the following elements: Sc, V, Mn. What do you notice about the number of protons and neutrons?
Each of these elements should have a few more neutrons than protons. By now some students should
begin to notice a pattern - as the mass gets bigger, the neutron to proton ratio increases. You may stop
the class here to point out this fact, when you notice that students are finishing their work in building
the atoms in this step.
Plot the number of protons versus the number of neutrons on the graph.
The students should end up with a plot that isn’t quite a straight line. The line will start out linear (p=n),
but the slope should gradually get steeper as the number of neutrons increases.
[Insert the completed graph here]
What pattern do you notice about the number of protons vs. neutrons as the mass of the atom gets bigger?
The number of neutrons gets bigger than the number of protons as the mass of the atom gets bigger.
Now look at some large elements like Pa, Pb, Bi, U on the periodic table. How do the numbers of protons
and neutrons compare to each other? Did you notice the same pattern as shown on your plot.
The number of neutrons for very heavy elements ends up being about 1.5 times the number of protons.
It should fit very well on the pattern on the students’ plot.
4
a. What element were the students building?
The students were building boron. The atom always has five protons, and boron has an atomic number
of five.
b. Fill in the atomic mass of each of the 8 atoms
The atomic masses are as follows: 11, 10, 11, 11, 10, 11, 11, 11. Point out here that if students were to
randomly sample individual atoms of an element with two isotopes, this would be a typical set of data.
c. Calculate the average atomic mass for the class.
The average atomic mass for the class is 10.75, or the average of the above values.
d. How does your average compare with the average atomic mass listed on the periodic table? Is it more
than the average mass listed in the table, less than, or about the same?
Our average atomic mass is only high by 0.05 amu - very close!
e. What must be different about the natural abundance of the two different isotopes compared to what
was built in this class.
Because the average atomic mass is closer to the B-11 isotope, then the B-11 isotope must be more naturally abundant.
Here the students will build a number of
smaller atoms. This will help them
visualize the relationships between
mass number, atomic number and the
number of each nucleon. Then the
students will graph their results and
investigate the patterns between the
number of protons and neutrons in the
nucleus.
The average atomic mass
Here the students explore why the
periodic table doesn’t have all round
numbers for the mass numbers of the
elements. They will explore a few
isotopes of one element, and take the
average of them to get an average
atomic mass. This will correspond
closely to what they see on the periodic
table.
160
Ideas and Dialog
Chapter 5: The Structure of the Atom
Investigation page
Sample answers
Example Answers
For the following answers, atoms are given as:
Atom(protons,neutrons).
3a. He(2,2), C(6,6), O(8,8). All these atoms have the same number of protons as
neutrons.
no. neutrons > no. protons
3b. Na(11,12), Al(13,14), P(15,16). All these atoms have one more neutron than the
number of protons.
3c. Sc(21,24), V(23,28), Mn(25,30). Each of these atoms has a few more neutrons than
protons.
protons=neutrons
In general, the number of neutrons is greater than the number of protons. The plot
deviates from the protons=neutrons line as shown on the adjacent plot.
4a. Boron.
4b. 11, 10, 11, 11, 10, 11, 11, 11.
4c. 10.75.
4d. The average is off by about 0.05 amu - very close!
4e. Because the average atomic mass is closer to 11 than 10, that means that B-11 must
be more abundant.
Teaching Tips
It may help if you all build one atom with the students together, to show them how to
build atoms quickly. Take an atom from the 2nd or 3rd row, so it doesn’t take too long.
First, say that the atomic number is the number of protons as well as electrons, and fill in
the marbles together. Then say that the atomic mass minus the atomic number gives the
number of neutrons, and fill in those marbles together.
5 A: Inside the Atom
161
Chapter 5
5B: Spectrophotometry
Key Question: How is color measured?
In this Investigation, students explore how color is measured, and how this measurement
is used in chemistry. They will explore the difference between absorption and
transmission, and what causes objects to appear certain colors. They will learn that
objects are a certain color because that object absorbs other wavelengths of light, and the
ones that aren’t absorbed are reflected back into our eyes.
Reading Summary
Questions and Goals
Students read section 5.4 (Light and
Spectroscopy) before performing the
investigation.
If the energy levels of electrons are different for
different elements, then the light emitted must also be
different. In fact, each element emits a characteristic
spectrum. Chemists refer to the emission spectrum as
the “fingerprint” of an element. Chemical laboratories
routinely identify elements and compounds by their
spectra.
Atoms both emit and absorb light at the energies
corresponding to their energy levels. If white light is
passed through a sample of matter, some light will be
absorbed by the atoms in the sample. Not all light will
be absorbed, however. Only colors corresponding to
specific energy levels are strongly absorbed, resulting
in dark lines in a continuous spectra. This is called an
absorption spectra. Can you see the similarities
between the absorption spectra and emission spectra?
162
Main • How is light measured?
Questions • What is the difference between transmission and absorption?
• What makes an object appear a certain color?
Learning By the end of the Investigation, students will be able to:
Goals • Know the difference between transmission and absorption.
• Explain why objects appear certain colors.
• Know how to use absorbance to measure amounts of different colors.
Key Vocabulary Transmission, absorption, spectroscopy, color.
Chapter 5: The Structure of the Atom
Materials and Setup
Each group should have:
•
•
•
•
•
•
•
One LabMaster, fully charged
Five cleaned and dried cuvettes
One pack of food coloring
One cuvette stand
Tap water
Four test tubes
Three clean pipettes
Teaching Time One class period
Preparation Set up a charged LabMaster, a cuvette stand and a
pack of food coloring ready at each station. You
must also have five cleaned & dried cuvettes, and
three cleaned & dried test tubes ready for each lab
group.
Assignments Section 5.4 (Spectroscopy) in the Student Edition
before the Investigation.
Preparation
You will need to set up each lab station so that the students are
ready to use it. Each station should have a charged LabMaster, a
cuvette stand, and a pack of food coloring droppers. Four-packs of
food coloring (red, yellow, green, blue) can be purchased from
most grocery stores. Each group should have five cleaned and
dried cuvettes, and three cleaned and dried test tubes. This will
save time during the investigation. Students can answer the
questions in part 4 at home if time runs out.
Hints:
• Explain to the students the need to make each solution have the
same height (volume). This will increase the accuracy of their
measurements. This is because some light is reflected off the
water-air interface, and as long as this interface is at the same
height, the effect will be the same across all samples.
• One pack of food coloring should provide enough material for
at least ten lab groups.
Misconceptions Students think that the absorbance of the color,
which corresponds to the color of the solution,
should be high. For example they are initially
confused when a red solution has a low red
absorbance.
Spectrophotometry
Students work in groups of two or three at tables.
5B
Details
Outline of the Investigation
1
2
3
4
Preparation of solutions
Absorption and color
Increasing the concentration
Things to think about
163
Investigation sections
Preparation of solutions
Part
1
Prepare the solutions with the students,
while explaining why each step is
performed as it is. Explain why the
solutions must be at the same height.
Absorption and color
2
Students explore absorption and how it
relates to food dyes. They will notice
that ‘single color dyes’ absorb all colors
to different degrees, and the relative
amounts of absorption make it appear
that color.
Increasing the concentration
Here the students increase the
concentration of their food colorings
linearly, and watch as the absorbance
does not increase linearly. They will
then learn about the logarithmic nature
of absorbance, as they graph the data
they collect from adding drops of food
coloring.
164
3
Ideas and Dialog
Put one drop of food color in each test tube. Add 10 mL of water to each test tube and mix.
The students should make sure that all the food coloring is dissolved, or that no coloring is splattered on
the walls of the test tube away from the water. This will help standardize the concentrations.
Using the small pipette, take 3 mL of each solution and put it in the cuvettes. So far you have four cuvettes
each with a different color.
It is vital that the solutions all have the same height, or as close as possible. This will make the accuracy
of the measurements much higher. This is because light from the LEDs in the LabMaster reflects off the
surface of the water, and if all the surfaces are at the same height, the effect will be the same across the
samples.
Now put 2 mL of water in the fifth cuvette. This cuvette will be used as a reference in your measurements.
This solution functions as the control, because even tap water does absorb some light. It should be at
the same height as all the others too.
Activate the spectrophotometer of your Lab-Master by pressing the RGB on button.
Once the LabMaster is on, just press RGB once to activate the spectrophotometer. If students are having trouble, turn the device off and on, then try again. It is possible that they have played with the buttons, and are in a different mode.
Use the clear cuvette and the Reference button to calibrate the spectrophotometer.
Here the students will put the cuvette with tap water in the LabMaster and hit “Reference” to calibrate
it. Explain to the students that absorption here is a relative measurement, and we want to know how
much light food coloring absorbs relative to tap water. This way, the values for pure tap water should
end up being very close to zero.
3. Measure the RGB values for each cuvette, including the clear reference cuvette and record your data on
Table 1 under the ‘1 drop of color’ column.
Here the students will likely notice that each dye absorbs some of each color. This is because the dyes
do not absorb pure colors. The way the students will know the color is by seeing which color is
absorbed the least, or transmitted the most. For example, red dye will absorb lots of green & blue and a
little red. Therefore the values for red absorbance will be lower than the other two.
We will now increase the concentration of the color in the solutions. Discard the solutions in the test tubes
and the cuvettes.
We do this because we want to ensure that the solutions are at the same height again. To do this, we
have to start over, adding food coloring first and then adding water to top it off.
Rinse the test tubes and cuvettes and pipette with clean water.
Make sure the students wash the cuvettes out until absolutely no color is left, or it will change their
results.
Add two drops of food color in each test tube. Repeat steps 2 - 4 of Part 1. Take absorption measurements
of the new solutions by repeating the steps in Part 2. Record your data on Table 1 under the ‘2 drops of
color’ column. Repeat the entire procedure once more by adding three drops of food color in the test tubes.
Don’t forget to have the students wash their test tubes after step 6, and to measure the control EVERY
TIME. This is to check if the LabMaster is changing its calibration (it shouldn’t!), but it is good scientific practice to do so.
Chapter 5: The Structure of the Atom
Investigation page
Sample answers
Teaching Tips
Go through the procedure with the students the first time. Do it one step at a time, and
have them raise their hand if something is amiss. This way most common problems will
be solved quickly and together, and all the rest of the spectrophotometry labs will go
much more smoothly.
Emphasize that all the solutions must be at the same level, because of the reflection off
the surface of water. To illustrate this, get a pan of water and shine a light (laser, LED,
flashlight...) on it. Have the students note how the surface acts like a partially reflective
mirror. Also mention that the same effect works underneath the surface as well as above,
because it is due to a change in the refractive index at the surface (water to air) that
causes this reflection. This is the same reason that a student’s glasses reflect some light,
or how windows can be see-through at a steep angle, and reflective at a shallow angle.
5 B: Spectrophotometry
165
Investigation sections
Things to think about
This part makes an ideal homework
assignment for the students if you run
out of time. If there is extra time to kill,
have them start answering the questions
so you can help them. The last question
will require research at home anyway.
166
Part
4
Ideas and Dialog
Explain what the values of R, G, and B mean in terms of the energy of light.
See Example Answers.
Is white a color or is white light a mixture of all colors? How do you know? How can you test this?
See Example Answers.
Also explain that rainbows are created from the white light of the sun, and the water droplets in the air
after rain act as prisms to split the light. If students wonder about rainbows more, point out that rainbows in the sky ALWAYS face opposite the position of the sun.
Explain the diagram on the right. How is the color green produced?
The color green is produced in an object when it absorbs all the other colors. Therefore, a green object
doesn’t emit green light - it just absorbs all the others. What does this say about plants? If they don’t
absorb green light, then that means that they don’t use it!
Which color was absorbed most strongly by the yellow dye? What colors were transmitted more?
See Example Answers.
Make a graph showing how the absorption changes with one, two, and three drops of food color.
Students will notice that absorbance increases non-linearly with food coloring concentration.
What does the absorbance of R, G and B tell us about the way the yellow color in our experiment is made?
Because all colors were absorbed some in the yellow food coloring, that means colors are produced by
relative absorbances. If an object absorbs less yellow than other colors, then it will appear yellow, even
if it absorbs some yellow light.
What do you notice about the way that the R, G and B absorbance values change for each solution? Do the
dye molecules in food color absorb a single color of light or a range of colors? How do you know?
The dye molecules absorb a range of colors, because all colors are somewhat absorbed. If they only
absorbed one color, then the other colors’ values would have been zero.
Research the way color books and magazines are printed. Explain the acronym CMYK. Why do printers
use CMYK color instead of RGB?
See Example Answers.
Chapter 5: The Structure of the Atom
Investigation page
Sample answers
Example Answers
4a. Red light is the least energetic. It has a wavelength of 620-670nm, and wavelength
is inversely proportional to energy. Green is between 520-550nm, and blue is
between 440-480nm.
4b. White light is a mixture of all colors - it is not a pure color. To test this, shine a
white light source (light bulb, flashlight, white LED...) through a prism, or any
angled piece of glass. You should see the colors ‘separate.’
4c. The color green is produced in an object when it absorbs all the other colors.
4d. Blue should be most absorbed by the yellow dye, because the wavelength of blue
light is farthest from the color yellow. Red and green should be transmitted more.
4e. Use the data from Table 1 to draw the graph.
4f. Because all colors were absorbed some in the yellow food coloring, that means
colors are produced by relative absorbances. If an object absorbs less yellow than
other colors, then it will appear yellow, even if it absorbs some yellow light.
4g. The dye molecules absorb a range of colors, because all colors had some absorption
measured.
4h. CMYK stands for ‘cyan magenta yellow key (black).’ Key stands for black in this
acronym. These colors were chosen instead of RGB (red green blue) because
combining two of the colored inks causes either red, green or blue to be absorbed.
For instance, cyan and magenta ink together absorb all the wavelengths except for
red, and red light is reflected off that area of the paper. Black is called ‘key’ because
all the colors’ positions are ‘keyed’ to the black ink’s position - it acts as the master
template. This is a subtractive color scheme, because it works by color absorption
(subtraction) instead of transmission (addition).
5 B: Spectrophotometry
167
Chapter 5
5C: Spectroscopy
Key Question: How is color used to identify elements?
In this Investigation, students explore how certain elements emit and absorb certain
wavelengths of light, which are related to the energy levels of the electrons in the atom.
Students will first explore spectroscopy by looking at individual element spectra, and then
they will explore the combination of multiple elements to create more complex colors and
spectra.
Reading Summary
Questions and Goals
Students read section 5.4 (Light and
Spectroscopy) before performing the
investigation.
Using spectra to analyze substances is called
spectroscopy. Spectroscopy can tell you what
elements produced the light being observed.
Spectroscopy is a tool for knowing what distant stars
are made of, identifying unknown compounds at a
crime scene, and even identifying forgeries. Right
now, satellites are searching for water on Mars and
astronomers are studying the composition of distant
stars and galaxies by using spectroscopy. Even the
makeup of our own atmosphere and global scale
environmental research is done via satellites using
spectroscopy.
168
Main • How is color used to identify elements?
Questions • Why does each element have a characteristic emission or absorption
spectrum?
• What is the difference between emission and absorption spectra?
• How is this information used to our advantage?
Learning By the end of the Investigation, students will be able to:
Goals • Know the difference between emission and absorption spectra.
• Know that each element has a characteristic spectrum, and explain why each
element has one.
• Know how we can use elemental spectroscopy to our advantage.
Key Vocabulary Spectrum, emission spectrum, absorption spectrum, spectroscopy.
Chapter 5: The Structure of the Atom
Materials and Setup
Each group should have:
• One complete pack of element spectroscopy cards
Preparation
You will need to ensure each group’s pack of cards is complete.
Be prepared to redistribute lab groups if necessary. Performing the
exercises yourself before the lab period will help you immensely
in explaining the concepts and answers to the students.
Hints:
• Explain the concept of emission spectra right away, so students
understand that these are the wavelengths of light that the atoms
emit when excited. If you have some gas discharge tubes &
prisms, now would be the time to demonstrate them.
• Mention that the atom’s electron energy levels control the
wavelengths of light affected, and that an atoms emission
spectrum is exactly opposite its absorption spectrum.
Teaching Time One class period
Preparation Make sure each group has a complete pack of
element spectroscopy cards. Replace any cards that
are missing or too damaged to use, and combine lab
groups if necessary.
Assignments Section 5.4 (Spectroscopy) in the Student Edition
before the Investigation.
Misconceptions Students think that the line spectra for different
Spectroscopy
Students work in groups of two or three at tables.
5C
Details
elements will be similar if the number of electrons
contained in the element are similar. For example, if
the atomic numbers for two elements are close, they
think the line spectra will be similar.
Outline of the Investigation
1
2
3
4
The spectrum cards
Learning to use the spectrum cards
Spectral identification
Thinking about what you have learned
169
Investigation sections
The spectrum cards
Part
1
The following concepts should be explained so that all students understand before proceeding to part 2:
-Wavelengths of light - higher wavelength means lower energy and vice versa
-The scale shows the entire possible spectrum - NOT the spectrum for the atom
-All the cards show emission spectra for the elements, or the wavelengths that the atom emits when
excited by a high voltage
-The absorption spectrum is exactly opposite the emission spectrum for an element
-The information on the bottom of the card shows the element’s name and atomic symbol
2
What element has a signature of three spectral lines grouped together at 655 nm?
See Example Answers.
Point out that some spectral lines can be very close, and students will have to match all the lines in an
element to get a match - not just some. This is because one type of atom always has the same energy
levels - no exceptions!
What element has double green line near 584 nm? What element has a gap between 500 and 610 nm with
no spectral lines in between?
See Example Answers.
Point out how close some of these double lines can be, and that the students have to look very closely to
see if there is a double or triple line.
Which element has the fewest spectral lines of the elements on the cards? Can you suggest a reason why
this element has the fewest number of spectral lines?
Hydrogen has the fewest lines, because it has the fewest number of electrons (1) and therefore the fewest number of possible energy levels.
Do you notice a pattern between the atomic mass of an element and the number of spectral lines?
The higher the mass of an element, the more spectral lines it will contain. That is because each electron
has a certain number of energy levels, which all correspond to unique spectral lines.
Explain the different parts of the cards
so that students can use them
effectively for the rest of the lab. A
student should be able to pick up any
card and understand all parts of it
before continuing.
Learning to use the spectrum
cards
Here a number of easy questions are
presented, with the goal of getting the
students to understand how to use the
cards for the next parts of the
investigation.
170
Ideas and Dialog
Chapter 5: The Structure of the Atom
Investigation page
Sample answers
Example Answers
2a. Beryllium
2b. Nitrogen
2c. Boron
2d. Hydrogen, because it has the fewest electrons.
2e. The higher the mass, the more spectral lines there are.
5 C: Spectroscopy
171
Investigation sections
Spectral identification
Part
3
This is the meat of the lab - expect the
students to spend 10-30 minutes
matching spectra. This isn’t supposed to
be too easy! Ask to see the ‘match’
once the student says he/she has found
it. If it is wrong, point out generally
why. Remember - only a perfect match
is correct!
Thinking about what you have
learned
This one question is best addressed in
the last two minutes of the lab period,
together with all the students. It helps
explain why this is useful, and will then
make them more interested by showing
that it is useful outside the classroom.
172
Ideas and Dialog
The spectral lines are a characteristic signature of each element. When elements are combined they retain
their spectrum signatures. If elements are mixed, the spectrum shows the lines of each separately. Scientists
can use the patterns of lines to identify each element present in the mix. Try it for yourself. Use the cards to
solve the following puzzles.
Here the students will attempt to match the ‘unknown’ spectrum cards printed in the lab manual with
the ‘known’ spectrum cards in the pack. Only a perfect match is acceptable - ask to see each one once
the students say they have found it.
This should get the students to fully understand how spectra can be combined to identify unknown
compounds. All that has to be done to do so is take an emission spectrum, and match up elements to
determine what is in an unknown compound!
4
Astronomers use the same technique you just used to figure out the age of stars. How can they use the spectral lines coming from a star to figure out its age? You may have to research this topic online.
Stars contain certain elements depending on their age. They often start out with only hydrogen or
helium - our sun is a good example. These function as the star’s fuel for nuclear fusion. As the star
ages, and runs out of hydrogen or helium, it begins to burn the helium (again by nuclear fusion) into
heavier elements, such as carbon and oxygen. This process continues all the way to iron - the element
which cannot be fused by stars. The relative amounts of each element help to determine the age of the
star, or at least the age phase of the star.
This is used by scientists to help discover extraterrestrial planets. If a star has an elemental signature
and size similar to our sun, there’s a good chance that there may be suitable planets near it. It helps
astronomers find good starting points in their search for extraterrestrial life!
Chapter 5: The Structure of the Atom
Investigation page
Sample answers
Example Answers
3. Answers to the challenge cards:
A: Nitrogen
B:Lithium
C: Beryllium
D: Hydrogen and helium
E: Mercury
F: Oxygen and helium
G: Gold and zinc
H: Platinum
I: Oxygen and carbon
4. See Part 4 Dialog for full answer. Any partial answer is acceptable.
Teaching Tips
Now would be the best time to illustrate gas discharge tubes if you have them, to show
where the spectral lines come from. Hydrogen and helium would help, as would neon
(any neon sign will do). All you need is the discharge tube, an exciter, and either a prism
or diffraction cards, available from most chemical suppliers for pennies apiece.
5 C: Spectroscopy
173
Chapter 5 Solutions.
Vocabulary
Match each word to the sentence where it best fits.
Section 5.1
element
law of definite proportions
law of conservation of mass
1. The law of definite proportions tells you that every molecule
of carbon dioxide has one atom of carbon to two atoms of oxygen,
even the frozen carbon dioxide found on Mars.
2. If you have a/an element then you can’t break it down into a
simpler substance.
3. The law of conservation of mass means that you must end
with everything that you start with.
Section 5.2
cathode ray
x-ray
electron
radioactivity
phosphorescence
nuclear radiation
4. When Becquerel was experimenting with uranium he accidentally
discovered radioactivity.
5. When glow in the dark materials give off light, it is called
phosphorescence.
6. The first subatomic particle to be discovered was negative with
almost no mass, and became known as a/an electron.
7. A/An cathode ray can be deflected by a magnet or electric field
because it is actually made of negatively charged particles.
8. Various kinds of nuclear radiation are given off by unstable
atoms, and can penetrate materials to different depths.
174
9. A/An x-ray is a form of light that can penetrate through paper (and
other materials).
Section 5.3
electromagnetic radiation
ground state
wavelength
excited electron
frequency
spectroscopy
10. The frequency tells us how often a wave moves up and down per
unit time.
11. Using spectroscopy astronomers can tell what distant stars are
made of.
12. Photons of electromagnetic radiation can be radio waves,
microwaves, infrared light, visible light, ultraviolet light, x-rays or
gamma rays.
13. Electrons give off light as they travel back down to their ground
state.
14. A short wavelength indicates a higher energy wave.
15. When an electron absorbs energy it becomes a/an excited
electron.
Section 5.4
uncertainty principle
atomic mass
orbital
isotopes
atomic number
ion
mass number
16. A/An ion is an atom (or small molecule) that has an unequal
amount of protons and electrons.
17. The mass number describes the number of protons and
neutrons.
A NATURAL APPROACH TO CHEMISTRY
Chapter 5 Solutions.
18. Calculating the atomic mass involves using a weighted average
of the masses of the isotopes.
19. A/An orbital describes where you are likely to find an electron.
20. Because of the uncertainty principle, we can only know the
location or the momentum of an electron, but not both at the same
time.
21. The atomic number tells us what kind of element an atom is.
22. Every atom of a particular element has a nucleus with the same
number of protons. However, the number of neutrons in the nucleus
can be different, making different isotopes.
Conceptual Questions
Answer: Alchemists wanted to turn elements into others particularly lead into gold. Chemists understand that
elements cannot be changed in chemical reactions.
25. Give at least two experiments that support the idea that everything
is made from atoms, and explain why.
Answer: 1) The emission spectrum of an element is the
same no matter how much you have. This suggests a
smallest unit of that element. 2) Elements form
compounds in whole number ratios, suggesting there is a
smallest quantum of an element or an atom.
26. Describe in your own words the law of conservation of mass.
Section 5.1
23. Draw a time line showing the development of atomic theory starting
with Democritus and ending with Heisenberg. Be sure to mention
the person, a date, and their contribution to our current knowledge
of the atom.
Answer:
400BC
24. What was the main goal of the alchemists, and how did this differ
from the chemists that followed them?
1800
1905
1910
1920
1927
Answer: Mass cannot be created or destroyed in a
chemical reaction. The mass of everything on one side of a
chemical equation must be the same as the mass on the
other side.
27. Describe in your own words the law of definite proportions.
Answer: Every molecule of one type will have the same
proportions of atoms in it.
28. Which parts of Dalton’s atomic theory are now known to be untrue?
Democritus
Proposed
the idea of
the atom
Dalton
Atoms of
the same
element
are alike.
Chemical
reactions
rearrange
atoms
Thomson
Rutherford
Discovered Discovered
the electron the atomic
nucleus
Bohr
Discovered
electron
orbits and
energy
levels
Heisenberg
Discovered
the
uncertainty
principle
Answer:
-The part that atoms are indivisible
-The part that all atoms of an element are identical
Section 5.2
29. What was the first subatomic particle to be discovered?
Answer: The electron
30. Describe the connection between cathode rays and electrons.
A NATURAL APPROACH TO CHEMISTRY
175
Chapter 5 Solutions.
Answer: Cathode rays are made of electrons
31. Explain how J. J. Thomson determined that cathode rays are made
from tiny, negatively charged particles.
Answer: He showed that cathode rays were attracted
towards a positively charged plate and away from a
negatively charged plate.
32. What is the “plum pudding” model of the atom?
Answer: This model proposed that the atom was made of
negatively charged electrons in a base, or “pudding,” of
positively charged matter.
33. Becquerel discovered which of the following:
a. phosphorescence
b. x-rays
c. radioactivity
d. radio waves
Answer: c
34. What are the three main types of nuclear radiation and how are they
different from each other?
Answer: Alpha particles - heavy charged particles
consisting of two protons and two neutrons (a helium
nucleus)
Beta particles - light charged particles (electrons)
Gamma rays - photons of high energy light with no charge
and almost no mass
35. Which is the only kind of nuclear radiation that is also an
electromagnetic wave?
Answer: gamma radiation
Answer: A beta particle has the same mass as an electron.
It usualy emitted by a nucleus and has a negative charge.
37. Explain why Rutherford's experiment proved that the plum pudding
model of the atom was incorrect.
Answer: Rutherford’s experiment proved that the
electrons were far outside the nucleus, rather than being
equally distributed in a positive atom center. The
deflection of alpha particles showed that the nucleus
contained all the positive charge in a very small space in
the center of the atom.
38. Given Rutherford's results, why did he determine the nucleus of an
atom was small, dense and positively charged?
Answer: In Rutherford’s experiment alpha particles were
shot on to a thin foil made of gold. The alpha particles are
positive and so by the way they were deflected he deduced
that the nucleus is positively charged. Since only very few
alpha particles were deflected he deduced that the nucleus
must be very small compared to the size of the atom. The
alpha particles were traveling with very high velocity and
so only something very dense could deflect them.
39. From what particles are atoms constructed, and where are they
located in the atom?
Answer: Protons and neutrons are located in the nucleus
(at the center of the atom) and electrons orbit the nucleus.
40. Which subatomic particle has almost no mass relative to the others:
the proton, the neutron or the electron?
Answer: The electron
36. Describe the connection between an electron and a beta particle.
176
A NATURAL APPROACH TO CHEMISTRY
Chapter 5 Solutions.
Section 5.3
41. Compare nuclear radiation to electromagnetic radiation. How are
they different and how are they similar?
Answer: Of the three types of nuclear radiation, gamma
radiation is also electromagnetic radiation. The other two
types (alpha and beta) are made of particles, which are not
electromagnetic radiation.
42. Using the diagram below, compare the wavelength, frequency and
energy of the two waves:
electrons that they collide with, and thus eject them from
their orbits.
46. How does an electron absorb energy?
a. It jumps to a higher energy level.
b. It heats up.
c. It moves closer to the nucleus.
d. It jumps to a lower energy level.
Answer: a
47. How does an electron emit a photon of light?
a. It jumps to a higher energy level.
b. It heats up.
c. It moves farther away from the nucleus.
d. It jumps to a lower energy level.
Answer: d
Answer: Wave A compared to wave B has:
a lower frequency
a larger wavelength
a lower energy
43. Which type of electromagnetic radiation carries more energy per
photon, microwaves or visible light?
Answer: Visible light
44. Which type of photon has more energy: a red photon of visible light
or a blue photon of visible light?
Answer: A blue photon of visible light
45. Explain why shining an intense red laser at a particular metal does
nothing, while a very weak ultraviolet light can cause electrons to
be ejected from the atoms.
Answer: The photons in ultraviolet light have more
energy than the photons in red light. The higher energy
photons in the ultraviolet light transfer more energy to the
A NATURAL APPROACH TO CHEMISTRY
48. Name three different ways you can excite an electron (give it more
energy).
Answer:
1. With electromagnetic energy (photons)
2. Collisions with other electrons
3. Collisions with protons or other charged particles
49. What is spectroscopy, and how can it help us learn about distant
stars, planets and our own atmosphere?
Answer: Spectroscopy is the study of the electromagnetic
energy that is emitted by atoms as their electrons go from
a higher energy level to a lower energy level. Each atom
has a unique signature of emitted electromagnetic energy.
By observing the spectrum light that comes from stars, we
can infer the type of atoms that are present in those stars.
177
Chapter 5 Solutions.
50. If you shine a light into a prism, it:
a. creates new types of light so you see photons other than the
color of the original light.
b. separates the photons that were mixed together in the original
beam of light.
c. subtracts some of the photons that were in the original light.
Answer: b
51. If an electron has four possible different energy levels, how many
different photons of electromagnetic energy could be given off by
that electron, assuming it keeps absorbing and releasing energy so
that it visits every possible energy level?
a. two
b. four
c. six
d. eight
Answer: c
Section 5.4
52. What is the main difference between the Bohr model and the current
orbital model of the atom?
Answer: In the Bohr model, the electron is considered to
be a particle well defined in space. In the current model,
the electron is considered to be smeared out into a wave
over a region of space.
53. Why did Bohr think electrons were orbiting in fixed orbits with
fixed energy levels?
Answer: Because he was able to explain the well defined
energies that were emitted from excited atoms.
54. Describe the difference between an orbit and an orbital.
Answer: An orbit is a well defined path, usually circular,
on which electrons are confined to move. An orbital is a
178
group of quantum numbers that have similar shapes in
space.
55. Why do we need to use probability maps like the orbital picture to
show where the electron is? Why can’t we say the electron orbits
the nucleus like a planet?
Answer: Because the probability (chance) of finding the
electron is not the same at any place in space. Only
electrons in the s-orbital have an equal chance to be found
at any angular position around the nucleus.
56. What number is the same for all oxygen atoms?
a. the number of protons
b. the number of neutrons
c. the number of electrons
Answer: a
57. What is the number on the periodic table that tells you which kind
of element an atom is?
Answer: the atomic number
58. If you have an atom of carbon-12 and an atom of carbon-14 then
you have:
a. two different ions
b. two different elements
c. two different isotopes
Answer: c
59. Describe the difference between the mass number for an atom and
the atomic mass of an element.
Answer: The mass number is the sum of the number of
protons and neutrons in the atom. The atomic mass of an
element is the average mass number of all isotopes of that
element.
A NATURAL APPROACH TO CHEMISTRY
Chapter 5 Solutions.
60. Give two examples of how rubbing things together can cause an
electric charge to build up.
Answer: Examples can involve anything that generates
static electricity, from rubbing your socks on a carpet to
rubbing a cloth on a glass rod to the belt and brushes on a
Van de Graff generator.
61. Explain why rubbing almost anything together can cause an electric
charge to build up.
Answer: Rubbing two materials often causes electrons to
be stripped off one onto the other, causing a charge to
build up.
62. If something is electrically neutral, then which one of the following
must be true?
a. It is constructed only from neutrons.
b. The positive and negative charges are exactly balanced.
c. It has been discharged by touching something metallic.
d. It is made from an equal number of protons and neutrons.
Answer: b
63. What must be true of the lithium atoms in a lithium ion battery - the
kind that power most laptops?
Answer: The lithium atoms must be ionized in order to
conduct and move charge.
Quantitative Problems
Section 5.1
64. An experiment was performed to measure the respiration reaction
common in most organisms. The following measurements were
taken:
Starting Materials
Ending Materials
sugar = 2.00 g
water = 1.20 g
oxygen = 2.13 g
carbon dioxide = 2.93 g
Does this experiment satisfy the law of conservation of mass?
Why or why not?
Answer: Yes it does. The mass of the starting materials is
equal to the mass of the ending materials.
(2.00 g + 2.13 g) = (1.20 g + 2.93 g)
65. An experiment was done to compare the carbon and oxygen
contents of carbon dioxide found in three different samples. The
samples came from Earth, a passing comet, and a meteor that
originated from Mars. Below is the data:
Sample
carbon (g)
oxygen (g)
Earth
3.00
8.00
comet
0.15
0.40
Martian
meteor
6.00
16.00
Does the data above support the law of definite proportions? Why or
why not?
Answer: Yes it does. The proportions of oxygen to carbon
in each sample are the same.
(8 ÷ 3) = (0.40 ÷ 0.15) = (16.00 ÷ 6.00) = 2.67
A NATURAL APPROACH TO CHEMISTRY
179
Chapter 5 Solutions.
66. If the nucleus of an atom is about 1/10,000th the radius of an atom,
what percentage of the volume of the atom is empty space,
assuming the atom is a perfect sphere?
photons, but when it jumps to level 1, ultraviolet photons are
emitted?
Answer: 99.999%
Remember that the sphere is (4/3)×π×r3, so the ratio
between the volumes is 1 to (1/10,000)3
67. Make up some analogy that gets across how big an atom is
compared to its nucleus. For example: If the nucleus were as big as
a baseball (about 3.5 cm radius), the outer edge of the atom would
be about 3.5 football fields away (about 350 meters or 35,000 cm).
Answer: This is open ended, but any answer where the
radii are in a 1:10,000 ratio is correct. For example, if the
atom were the size of the moon (1,750 km), then the
nucleus would be the size of 1.75 football fields (175 m).
Section 5.2
68. Below is a diagram showing which kinds of electromagnetic
radiation are produced when an electron jumps from a higher
energy level to a lower one. Why does it make sense that when an
electron jumps from a higher level to level 3 that it emits infrared
Answer: It all has to do with the difference in the energy
between the various levels. Ultraviolet radiation has a
higher frequency, and thus a higher energy when
compared to infrared radiation. The larger the difference
between the electron levels, the higher the energy that is
released when electrons move across them.
69. If you have an instrument that uses microwaves with a frequency of
1012 Hz, what is the energy in (ev) and the wavelength in (nm)?
Answer: Energy = 0.0041 ev. Wavelength = 300,000 nm
E = h × c / λ, c = f × λ
70. An electron absorbs an amount of energy equivalent to 12.75 eV,
and three photons are emitted as the electron loses energy and
returns to its ground state. The first photon has an energy of
0.66 eV, and the second photon has an energy of 1.89 eV. What is
the energy of the last photon emitted by that electron?
Answer: 10.20 eV
12.75 - 0.66 - 1.89 = 10.20; use conservation of energy.
180
A NATURAL APPROACH TO CHEMISTRY
Chapter 5 Solutions.
Section 5.3
74. Below is a table of ions or atoms. Fill in the table with the
appropriate numbers.
71. How many protons does a nitrogen atom have?
a. 7
b. 14
c. 28
d. It depends on the charge of the atom.
Element
lithium
Answer: a
72. How many electrons does a nitrogen atom have?
a. 7
b. 14
c. 28
d. It depends on the charge of the atom.
Protons
Neutrons
potassium
19
21
potassium
19
20
oxygen
8
7
A NATURAL APPROACH TO CHEMISTRY
Li
argon
Ar
nitrogen
N2+
nitrogen
N5-
Protons
Electrons
3
18
7
7
2
18
5
12
Answer: Because the number of electrons is equal to the
number of protons.
73. Below is a table of several different isotopes used in medical
imaging and research. Fill in the table with the appropriate numbers.
Isotope
1+
75. Explain why you don’t need the atomic symbol to determine the
number of electrons.
Answer: a
Element
Isotope
76. Calculate the approximate atomic mass for sulfur, given the
following isotopes and abundances:
sulfur-32: 94.93%
sulfur-33: 0.76%
sulfur-34: 4.29%
sulfur-36: 0.02%
Answer: 32.09
( 32 × 94.93) + (33 × 0.76) + (34 × 4.29) + (36 × 0.02)
100
181
Chapter 5 Solutions.
182
A NATURAL APPROACH TO CHEMISTRY