Name: __________________
Partner:_________________
Aim:
Exploring the Early Models of the Atom
Background: The model of the atom as we know it today has evolved over hundreds of years.
Many different scientists contributed to our current knowledge of Atomic Theory, including (but not
limited to) the three scientists highlighted in this activity: John Dalton, J.J. Thomson, and Ernest
Rutherford. Niels Bohr and Erwin Schrodinger are two atomic theorists that we will learn about in
future lessons.
Scientist #1: John Dalton - The Billiard Ball Model
 Look at the handout entitled “Early Models of the Atom”. This handout illustrates four early
models of the atom using three different elements. Examine Dalton’s Model of the Atom.
 1. Think about the properties of a billiard ball. What did John Dalton think about the
structure of atoms?
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Scientist #2: J.J. Thomson -The Plum Pudding Model
 Look at the handout entitled “Early Models of the Atom” again. Compare Thomson’s model of
the atom to Dalton’s model of the atom.
(spread out)
 2. Identify two things that Thomson added to the model of the atom.
a.______________________________________________________________
b.______________________________________________________________
Scientist #2: J.J. Thomson -The Plum Pudding Model (continued…)
 Thomson’s Experiment: Thomson performed an experiment using a cathode ray tube.
A cathode ray is now known to be a beam of electrons. Normally a cathode ray will travel in a
straight line when generated in a vacuum tube as shown below. (A vacuum tube is a tube
without any air in it.) This is what a normal cathode ray looks like in a vacuum tube:
 3. Highlight the path of the cathode ray.
 When positively and negatively charged plates are applied to the cathode ray, the ray
bends as shown below:
 4. Highlight the path of the cathode ray.
 5. The cathode ray bent towards the positive plate. What charge do you think cathode
rays (electrons) have (positive or negative), and why?
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 During his cathode-ray tube experiments, J.J. Thomson discovered that atoms contain
negative subatomic particles called electrons. Thomson also concluded that if there are
negatively charged particles in the atom, there must be positively charged particles in the
atom as well.
 6. What do you think would happen if there were ONLY negative charged
particles in the atom? (Hint: Think about what happens when you put negatively
charged things together.)
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Scientist #3: Ernest Rutherford – The Nuclear Model
The “Nuclear” Model
 Look at the handout entitled “Early Models of the Atom” again. Compare the examples of
Rutherford’s model of the examples of Thomson’s model of the atom.
 7. Identify the main change that Rutherford made to the model of the atom.
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 Rutherford performed an experiment using positively charged particles and a thin
piece of gold foil. Gold foil is like aluminum foil except that it is composed of gold (Au) atoms
instead of aluminum (Al) atoms. Rutherford shot the positively charged particles through
the gold foil and recorded where they ended up.
Over 
 Open the envelope labeled “Rutherford Card Set.” Each card in this set shows the path
of one of the positively charged particles through the gold foil. Shuffle the cards and place
them face-down in a pile. Draw one card at a time and look at the path of the
particle on the card.
 8. Draw the particle’s path on the picture below. If more than one particle travels
along the same path, make the line for that path thicker each time.
Rutherford’s Observations:
 9. What path do the particles take most often when they hit the gold foil?
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 10. What happens to the particles on rare occasions?
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 Complete the table below, which is a summary of conclusions drawn from Rutherford’s
experimental observations. What observations led to each of the two conclusions?
OBSERVATION
CONCLUSION
The atom is made up of mostly empty space.
The atom contains a dense, positive nucleus in
its center.
Scientist #4: James Chadwick – Discovery of the Neutron
For four years, James Chadwick was a prisoner of war in Germany. When
World War I ended, he returned to his native England to rejoin the mentor of
his undergraduate days, Ernest Rutherford. Rutherford oversaw Chadwick's
PhD in 1921 and then made him assistant director of the lab at Cambridge
University.
Chadwick worked day and night to prove the neutron theory, studying the
beryllium radiation with an ionisation counter and a cloud chamber. The
discovery of neutron quickly changed scientists’ view of the atom, and Chadwick was awarded the
Nobel Prize in 1935 for the discovery. Scientists soon realized that the newly discovered neutron, as
an uncharged (neutral) but fairly massive particle.
Summary of Early Atomic Theories
Draw the Dalton, Thomson, and Rutherford models for a Berllyium (Be) atom, using the
following symbols to represent the subatomic particles in your drawings.
Light red shaded circle = Diffuse positive charge
Dark red shaded circle = Proton
Blue shaded circle = Electron
Unshaded circle = Neutron
Fill in the table below based on what you learned during this assignment.
Name of
Model
Scientist
1.
Experiment
Major Conclusions
Various
experiments
combining
gases.
Billiard Ball
Model
Ex: 2H2+O22H2O
2.
J.J. Thomson
3.
4. Revised
Planetary
Model
Gold Foil
Experiment
James
Chadwick
Neutral particles
Experiments
(neutrons,
which have no
on the element
charge) exist in the
Beryllium
nucleus of an atom.
Practice Regents Questions
1. Which particle has no charge?
(1) electron (2) neutron
(3) positron
(4) proton
2. As a result of the gold foil experiment, it was concluded that an atom
(1) contains protons, neutrons, and electrons
(2) contains a small, dense nucleus
(3) has positrons and orbitals
(4) is a hard, indivisible sphere
3. In the late 1800s, experiments using cathode ray tubes led to the discovery of the
(1) electron
(2) neutron
(3) positron
(4) proton
4. Which subatomic particles are located in the nucleus of a neon atom?
(1) electrons and positrons
(2) electrons and neutrons
(3) protons and neutrons
(4) protons and electrons
5. Which statement describes the distribution of charge in an atom?
(1) A neutral nucleus is surrounded by one or more negatively charged electrons.
(2) A neutral nucleus is surrounded by one or more positively charged electrons.
(3) A positively charged nucleus is surrounded by one or more negatively charged electrons.
(4) A positively charged nucleus is surrounded by one or more positively charged electrons.
6. An experiment in which alpha particles were used to bombard thin sheets of gold foil led to the conclusion
that an atom is composed of
(1) empty space and has a small, negatively charged nucleus
(2) empty space and has a small, positively charged nucleus
(3) a large, dense positively-charged nucleus
(4) a large, dense negatively-charged nucleus
7. A student compares some models of the atom. These models are listed in the table below in order of
development from top to bottom.
a. State the model that first included electrons as subatomic particles. __________________________
b. State one conclusion about the internal structure of the atom that resulted from the gold foil experiment.
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c. Using the conclusion from the Rutherford model, identify the charged subatomic particle that is located in
the nucleus.
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d. State one way in which the Bohr model agrees with the Thomson model.
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