Download File

Document-Based Question
The Atomic Model: A Changing Understanding
Jackson County Comprehensive High School
Directions: The following documents focus on the development of the atomic theory and the individual steps that have led to our modern
understanding. You are to read/analyze each of the following documents in the order that they appear. Following each document you are
to answer the questions based upon your reading/analysis to the best of your ability. Then you will utilize the documents, your answers to
the questions, and your prior knowledge to write a well-organized essay based on the following prompt. The length of this essay should be
a minimum of five (5) paragraphs. Your essay should include an introductory paragraph followed by a body that includes specific details
from the documents that have been provided for you.
Essay Prompt: The theory of the atom has had multiple changed over the centuries, from a simple uncuttable piece to the complex
electron cloud model. What were the questions and problems with each model and how did the next model solve this problem? What
experiments, observations, etc. were used to modify the model of the atom? How did the electron play a role in these models?
Historical Background:
One of the first people to suggest the concept of the atom was Democritus, a Greek philosopher who lived in the fifth century
BC. Democritus knew that if a stone was divided in half, the two halves would have essentially the same properties as the whole.
Therefore, he reasoned that if the stone were to be continually cut into smaller and smaller pieces then; at some point, there would be a
piece which would be so small as to be indivisible. He called these small pieces of matter "atomos," the Greek word for indivisible.
Democritus claimed that atoms were specific to the material which they composed. In addition, Democritus believed that the
atoms differed in size and shape, were in constant motion in a void, collided with each other; and during these collisions, could rebound or
stick together. Therefore, changes in matter were a result of dissociations or combinations of the atoms as they moved throughout the
void. Although Democritus' theory was remarkable, it was rejected by Aristotle, one of the most influential philosophers of Ancient
Greece. Atomic theory was to lay dormant for 2,000 years as an idea, with people siding for and against it.
Although the idea of the atom was first suggested by Democritus, his suppositions were not useful in explaining chemical
phenomena, because there was no experimental evidence to support them. It was not until the late 1700's that early chemists began to
explain chemical behavior in terms of the atom. Joseph Priestly, Antoine Lavoisier, and others set the stage for the foundation of
chemistry. They demonstrated that substances could combine to form new materials.
It was the English chemist, John Dalton, who put the pieces of the puzzle together and developed an atomic theory in 1803.
Dalton's atomic theory contains five basic assumptions:
- All matter consists of tiny particles called atoms. Dalton and others imagined the atoms that composed all matter as tiny, solid
spheres in various stages of motion.
- Atoms are indestructible and unchangeable. Atoms of an element cannot be created, destroyed, divided into smaller pieces, or
transformed into atoms of another element. Dalton based this hypothesis on the law of conservation of mass as stated by
Antoine Lavoisier and others around 1785.
- Elements are characterized by the weight of their atoms. Dalton suggested that all atoms of the same element have identical
weights. Therefore, every single atom of an element such as oxygen is identical to every other oxygen atom. However, atoms of
different elements, such as oxygen and mercury, are different from each other.
- In chemical reactions, atoms combine in small, whole-number ratios. Experiments that Dalton and others performed indicated
that chemical reactions proceed according to atom to atom ratios which were precise and well-defined.
- When elements react, their atoms may combine in more than one whole-number ratio. Dalton used this assumption to explain
why the ratios of two elements in various compounds, such as oxygen and nitrogen in nitrogen oxides, differed by multiples of
each other.
John Dalton's atomic theory was generally accepted because it explained the laws of conservation of mass, definite
proportions, multiple proportions, and other observations. Although exceptions to Dalton's theory are now known, his theory has
endured reasonably well, with modifications, throughout the years.
Approximately fifty years after John Dalton's proposal of the atom, evidence began to accumulate which suggested that the atom
might not be the solid sphere that Dalton had envisioned. This evidence came in the form of the discovery of electrically charged particles
and radioactive materials. Based on these new discoveries, Dalton's proposal of a solid, indestructible atom became unacceptable. Listed
below, are a few of the significant discoveries and the theories developed from them.
- Adapted from www.abcte.org
All documents can be found at http://goakley.weebly.com/dbq.html, listed in order.
Part I – Read/view the following documents. Answer each question immediately following the individual documents.
Document A: J. J. Thomson’s plum-pudding atomic model: The making of a scientific myth
1.) Describe the model that J. J. Thomson developed?
2.) How did J.J. Thomson model the atom with his discovery of the electron?
3.) Many people called the model the “plum pudding” model. Is this an accurate description? Explain.
Document B: A science prototype: Rutherford and the atom
4.) Explain the Rutherford model of the atom.
5.) During Rutherford’s gold foil experiment, what did he expect the alpha particles to do and what actually happened?
6.) What are the ways that Rutherford and his team moved science forward?
Document C: The Bohr Model of the Atom
7.) How to the Bohr model differ from the Rutherford model?
8.) What could the Rutherford model not explain? How did the Bohr model explain it?
9.) How did the emission spectrum play a role in the development of the Bohr model?
Document D: The Electron Cloud Model
10.) How did the location of the electron change with the electron cloud model?
11.) What is the governing principle that led scientists to develop the electron cloud model?
12.) Describe how the electron can move within its shell.
Conclusion:
Describe the changes in the model with reference to experiments, observations, and the electron.
Score of 5
o Thoroughly addresses all aspects of the
task by accurately analyzing and interpreting
most of the documents.
o Incorporates relevant outside information
o Richly supports outline with relevant facts,
examples, and details
o Writes a well-organized outline,
consistently demonstrating a logical and
clear plan of organization.
o Includes a strong introduction
o Includes a strong conclusion
o Includes an original thesis statement
Score of 4
o Addresses all aspects of the task by
accurately analyzing and interpreting most
of the documents.
o Incorporates relevant outside information
o Supports outline with relevant facts,
examples and details-may be more
descriptive than analytical
o Writes a well-organized outline,
demonstrating a logical and clear plan of
organization
o Includes a good introduction
o Includes a good conclusion
o Includes a clear thesis statement
Score of 3
o Addresses most aspects of the task or all
aspects in a limited way
o Incorporates limited or no relevant
outside information
o Uses some facts, examples, and details-but
is more descriptive than analytical
o Writes a satisfactorily developed outline,
demonstrating a general plan of
organization
o States the theme in the conclusion
o Includes a thesis statement
Score of 2
o Attempts to address some aspects of the
task by accurately analyzing and interpreting
most of the documents
o Incorporates limited or no outside
information
o Uses few facts, examples, and detailssimply restates contents of documents
o Writes a poorly organized outline, lacking
focus
o Has a vague or missing introduction
o Has a vague or missing conclusion
o Lacks a clear thesis statement
Score of 1
o Shows limited understanding of the task
with vague, unclear references to the
documents
o Presents no relevant outside information
o Attempts to complete the task but
demonstrates a major weakness in
organization
o Uses few or no accurate or relevant facts,
details, or examples
o Has vague or missing introduction or
conclusion
Score of 0
o Fails to address the task
o Writing is illegible
o The essay is plagiarized
o Blank paper