Constructed Response
Development of the Atomic Theory
Teacher Guide
Students will need about 15 minutes to complete these constructed response tasks.
Objectives assessed:
• Trace the evolution of the atomic theory from ancient Greece to modern day, including
the contributions of key scientists.
1. The development of the atomic theory required many years and the hard work of many
scientists.
• Describe two experiments that were performed to support development of the
atomic theory.
• Describe three different versions of the atomic theory that were proposed over
time and identify who proposed them.
Correct response(s):
Sample Correct Response: Two experiments that helped move atomic theory forward were
the cathode ray tube experiment and the gold foil experiment. J.J. Thomson used a cathode
ray tube to determine that atoms contain negatively charged particles; he developed the
plum pudding model of the atom. Ernest Rutherford used the gold foil experiment to show
that atoms contain a positively charged central region called the nucleus, which contains
most of an atom's mass.
The versions of the atomic theory that developed over time included the following ideas:
• Democritus proposed that all matter in the world consisted of invisible and indivisible
corpuscles (or small particle-like objects). He called these corpuscles atoms.
• John Dalton theorized that matter is composed of atoms, that the atoms of each
element have unique properties, that atoms cannot be divided, created, or destroyed,
that atoms combine in simple ratios to form compounds, and that atoms are
rearranged during chemical reactions.
• Thomson proposed that atoms do contain smaller components when he discovered
negatively charged particles (electrons); he developed the plum pudding model of the
atom.
• Millikan’s oil drop experiment proved that electrons have mass and charge, which
clearly confirmed their existence.
• Rutherford discovered that atoms contain a positively charged central region called
the nucleus, in which is found most of an atom's mass.
• Niels Bohr discovered that hydrogen atoms orbit the nucleus at specific energy levels,
and that the electrons emit or absorb certain amounts of energy when they change
levels. Researchers have expanded on all these ideas to develop quantum theory,
which is based on the idea that energy is transferred to and from electrons in specific
amounts. The amount of energy an electron has determines its location in the
electron cloud surrounding an atom’s nucleus.
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© Discovery Communications, LLC
Response scoring tool:
Score
Content
5
Describes at least two of the key experiments shown in the sample
answer, including the contribution made to atomic theory; lists at least
three versions of the atomic theory as it evolved over time, including
information differentiating it from previous versions.
4
Describes at least two of the key experiments shown in the sample
answer, including the contribution made to atomic theory; lists two
versions of the atomic theory as it evolved over time, including
information differentiating each version from previous versions.
3
Describes one of the key experiments shown in the sample answer,
including the contribution made to atomic theory; lists two versions of the
atomic theory as it evolved over time, including information differentiating
each version from previous versions.
2
Describes one of the key experiments shown in the sample answer,
including the contribution made to atomic theory; lists one version of the
atomic theory as it evolved over time, including information differentiating
it from previous versions.
1
0
Describes either one of the key experiments shown in the sample
answer, including the contribution made to atomic theory, or lists one
version of the atomic theory as it evolved over time, including information
differentiating it from previous versions.
No response, or response not appropriate to the question.
Discovery Education Science
© Discovery Communications, LLC