Name: Teacher Answer Key
Atomic Theory
Discovering The Structure of The Atom
Station 1 - Vocabulary Map
Task: Look up the following words in the textbook and complete each portion of the vocab map.
Definition:
Negatively charged subatomic particle
found outside the nucleus
Picture:
Electrons
Varies
Sentence: Varies
Definition:
Positively charged subatomic particle
found inside the nucleus
Picture:
Proton
Sentence: Varies
Definition:
The central region of the atom, containing
the protons and neutrons, and making up
most of the atoms mass
Sentence: Varies
Definition:
A subatomic particle with neutral charge
found inside the nucleus
Sentence: Varies
Varies
Picture:
Nucleus
Varies
Picture:
Neutron
Varies
Name: Teacher Answer Key
Atomic Theory
Discovering The Structure of The Atom
Station 2 – Mini Lab: Evidence for Atoms (Textbook Resource: Holt Science Spectrum)
Task: Complete the following experiment and answer the questions that follow.
Materials: Balance, pennies, marbles, 2 cups (labeled “1” and “2”).
Each cup contains pennies & marbles in a predetermined amount. The pennies & marbles from each cup
should be weighed separately, do not combine the pennies & marbles from Cup 1 with the pennies &
marbles from Cup 2.
Step 1: Use a balance to find the total mass of the pennies in Cup 1. Mass of pennies (Cup 1) = _varies_
Use a balance to find the total mass of the marbles in Cup 1. Mass of marbles (Cup 1) =__varies_
Step 2: Use a balance to find the total mass of the pennies in Cup 2. Mass of pennies (Cup 2) = _varies__
Use a balance to find the total mass of the marbles in Cup 2. Mass of marbles (Cup 2) =__varies_
1. Compare the composition of the “compounds” in the 2 cups in terms of the proportions of
marbles and pennies by mass. Do the cups contain the same “compound”? Explain. _Because_
the ratio of pennies & marbles is different in each cup, they are not the same compound.
2. Based on your evidence, do you think that different substances could be made up of the same
elements, just different amounts? Explain. Yes. We have a limited number of elements, but
those elements are arranged differently (different proportions bond with different elements) to
give us all mater that we can observe. Two different items could be made up of hydrogen and
oxygen simply by having different hydrogen-oxygen ratios.
Station 3 – Timeline Research (Textbook Resource: Holt Science Spectrum - pgs 113-129)
Task: Research to find the following information.
When did Democritus develop his atomic theory? __400 BC____
What did Democritus suggest? He said that all matter is made up of indivisible units called atoms
What does the word indivisible mean? _It cannot be divided.___________________
Did everyone support Democritus’s theory? __No_ Why or why not? He did not have evidence
When did Dalton develop his atomic theory? __1808________
What did Dalton’s Atomic Theory say? All matter consists of indivisible particles called atoms. Atoms of
the same element are similar in shape and mass, but differ from the atoms of other elements. Atoms of
same/different elements can combine with each other to form compound atoms. Atoms are the
smallest unit of matter that can take part in a chemical reaction.
What law is used as evidence to support Dalton’s theory? _Law of definite proportions_____
When did Thomson develop his atomic theory? __1897_______
What instrument did Thomson use to develop his theory? ___cathode ray tube___
How was Thomson’s model different from Dalton’s model of the atom? _It contained electrons and said
that the atom could be divided_
What was Thomson’s model called? Plum pudding model
What did Rutherford say about the structure of the atom? It contained a massive central region called
the nucleus.
What was Rutherford’s experiment called? __Gold foil experiment___________________
Name: Teacher Answer Key
Atomic Theory
Discovering The Structure of The Atom
As a result of his experiment, what did Rutherford discover? __The nucleus of the atom_____
When did Bohr develop his theory? _1913______
What does Bohr’s theory say? _Electrons can be found in specific energy levels orbiting the nucleus __
Station 4 - Timeline
Task: Using the information from your research, complete the timeline to show the development of the
atomic theory.
The timeline should include
 The following scientist: Democritus, John Dalton, JJ Thomson, Ernest Rutherford, and Niels Bohr
 The date,
 A description of their major contributions,
 An illustration of the model of the atom at that specific date.
Atomic Theory Timeline
400 BC
Democritus said
that all matter is
made up of tiny
indivisible units
called “atomos”
1897 J.J. Thomson Using
the cathode ray tube
discovered that atoms
contained negatively
charged particles called
electrons – developed
his plum pudding model
1808 John Dalton studied the composition of gases to
determine that: All matter consists of indivisible particles
called atoms. Atoms of the same element are similar in shape
and mass, but differ from the atoms of other elements. Atoms
of same/different elements can combine with each other to
form compound atoms. Atoms are the smallest unit of matter
that can take part in a chemical reaction.
1913 Niels
Bohr said that
electrons can
be found in
specific energy
levels orbiting
the nucleus
1911 Ernest Rutherford
conducted his gold foil
experiment to
determine that the
atoms mass is contained
a dense center called
the nucleus.
Summary: Describe how scientific knowledge is open to change as new evidence is observed. As we see
with the atomic theory; as technology advances, new evidence is observed and if the evidence does not
match a previous theory, that theory is modified in order to take into account the new evidence. We
don’t continue to think of the atom in the same way that Democritus and Dalton thought of the atom
because we now know that subatomic particles exist.
Name: Teacher Answer Key
Atomic Theory
Discovering The Structure of The Atom
Station 5 – Read, Discuss, Write (Textbook Resource: Holt Science Spectrum)
Task: Read the following paragraphs, and complete the exercises below.
Seeing Atoms: The STM
The idea that everything is made up of small particles called atoms was first proposed by Greeks in the
fifth century BCE. At that time, there was no experimental evidence to support this theory, and it did not
gain much acceptance.
Much later, in the early 1800s, British scientist John Dalton made a convincing argument, based on
experimental evidence that supported the existence of atoms. Atoms are much too small to see, but
Dalton found evidence for them in things he could observe, such as reactions between compounds.
Because of the work of Dalton and others, the atomic theory soon became widely accepted by scientists.
How the STM Sees Atoms
Until recently, all evidence for the atomic theory was indirect. However, an exciting development in
1981 made it possible to see atoms for the first time. This new technology, the scanning tunneling
microscope (STM), uses an electric current to probe the surface of a material. The STM measures how
electrons are distributed on the material’s surface. The results are used to create a computer generated
image of the atoms on the surface.
The first image created by an STM showed a layer of gold atoms. Since then, the atoms of many
different substances have been observed with STMs, including silver, nickel, platinum, and silicon. At
this time, STMs are used primarily for imaging atoms. STMs have also been used to move single atoms
from one location to another, and other potential applications are being researched.
EXERCISES – Discuss the answers to the following questions then, on your own, write your response.
1. What is the most important difference between the Greek theory of atoms and Dalton’s atomic
theory?
Dalton was able to provide evidence.
2.What is the significance of the invention of the STM?
It will allow us to make even more observations of the atom and potentially provide new evidence for
the continued evolution of our knowledge of the atom
Station 6 – Creation Station: Model the Development of the Atomic Theory
Task: Use the items provided to build Dalton’s model of the atom, J.J. Thomson’s model of the atom,
Rutherford’s model of the atom, and Bohr’s model of the atom then answer the following questions.
Materials: Modeling clay (several colors)
Questions
1. Compare Thomson’s atomic model with Rutherford’s atomic model. Explain how they are the
same and how they are different. Thomson’s model of the atom only included electrons and
they were scattered all throughout the atom. Rutherford’s model included the nucleus and
showed that the electrons were found surrounding that nucleus.
2. Does the term indivisible still describe the atom? Explain. No. Because we know that it can be
divided into subatomic particles (nucleus, electron clouds, protons, neutrons, electrons, etc.)
Name: Teacher Answer Key
Atomic Theory
Discovering The Structure of The Atom
Station 7 – The Structure of Atoms
Task: Examine the diagram and think about the discoveries that each scientist made to develop the
atomic theory to answer the following questions.
1. What is the center of the atom called? _The nucleus_
2. The center of the atom is made up of positively charged particles and
particles that have no electrical charge. Name the two particles.
Particles with a positive charge = protons____
Particles with no charge = _neutrons_______________
3. Negatively charged electrons are found in clouds outside the center of
an atom. Why are electrons attracted to the center of the atom?
The negative charge of the electrons is attracted to the positive charge
of the protons found in the nucleus.
Use the items provided to build a model of a neutral Carbon atom. Draw your model (be sure to label
what each color represents) & explain it when you’re done.
Materials: 1 bowl, 30 balls (10 red, 10 black, 10 blue), colored pencils (red, blue, black), periodic table
Draw
Red represents ___protons or neutrons__________.
Yellow represents __protons or neutrons.
Black represents ____electrons
How many protons did you use? _6__
How many neutrons did you use? ___6___
How many electrons did you use? __6____
What does the bowl represent? The nucleus_____
Explain where you placed your subatomic particles and why you placed them in that location. Protons
and neutrons were placed inside the bowl since the bowl represented the nucleus. Electrons were
placed around the outside of the bowl since they are found in electron clouds outside the nucleus. _
How did you select the amount of protons, neutrons, and electrons that you chose to use?
Using the periodic table provided, the number of protons was based on the atomic number, the number
of neutrons was found by taking the atomic mass minus the atomic number and the number of
electrons equals the number of protons since the atom is neutral.
Name: Teacher Answer Key
Atomic Theory
Discovering The Structure of The Atom
Stations 8 – Lab Simulator: Build an Atom (Online Resource: phet.colorado.edu)
Task: Complete the lab simulator to answer the following questions.
1. Google Phet Build an Atom
2. Click on the first link.
3. Click on the RUN NOW button
4. Open the boxes called Symbol, Mass Number, and Net Charge.
5. Experiment by putting some protons into the nucleus of the atom (on the X).
Fill in the table to the right to keep
track of what you are learning
about protons.
When you finish, put the protons
back into the bowl.
Mass
number?
Charge?
positive
Changes
When you finish, put the neutrons
back into the bowl.
Mass
number?
Changes
Symbol changes on
the center
the periodic table?
(on the
X)?
6. Experiment by putting some neutrons
into the nucleus of the atom (on the X).
Fill in the table to the right to keep
track of what you are learning
about neutrons.
Stays in
Charge?
No
charge
Yes or No
Yes or No
Stays on
Symbol changes on
the X?
the periodic table?
Yes or No
Yes or No
7. Experiment by putting some electrons into the nucleus of the atom (on the X).
Fill in the table to the right to keep
track of what you are learning
about electrons.
When you finish, put the electrons
back into the bowl.
Mass
number?
Stays
Charge?
negative
Stays on
Symbol changes on
the X?
the periodic table?
Yes or No
Yes or No
the same
8. Look over your data tables for protons,
neutrons and electrons.
Two things we noticed are: 1. ____varies________________________
2. __varies_________________________________
9. Put 3 protons into nucleus of the atom. Fill in the following:
Name of atom:__Lithium____
atom or ion? ___ion___ net charge? ___+3______
10. Decide how you will build a neutral atom that is stable. Practice making atoms using your ideas.
List the steps that youwould take to build a neutral atom starting with protons:
1. First I choose _varies_ protons and put them in the center (nucleus) of the atom.
2. Varies
3. Varies
Name: Teacher Answer Key
Atomic Theory
Discovering The Structure of The Atom
Extension: Play the game!