Evidence for Atoms - CHF Chemistry WebQuest #2

CHF Chemistry WebQuest #2
Evidence for Atoms
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Introduction
Your Task
The Process
Resources
Evaluation
Conclusion

Introduction

Greek postage stamp
honoring Democritus.

In 400 B.C., the Greek thinker Democritus proposed that all matter was made of tiny indivisible particles, which he named atomos. But scientific investigation as we know it was not commonly practiced back then, and Democritus never carried out any experiments to see if his theory was correct. He had his supporters, and the Democritus University of Thrace was named in his honor, but lacking any solid evidence, his theory was rejected by Aristotle; and therefore the idea of atoms was likewise rejected by nearly everyone else for the next two thousand years.

John Dalton

Then, in the early 1800s, an English school teacher named John Dalton took the old idea of atoms and made it into something useful to modern science. How did this happen? Why did Dalton's idea catch on, while Democritus's didn't?

The fundamental principle behind what we call science today is the idea that we gain knowledge from evidence. We know something scientifically if we can point to some experience that proves it. What evidence did scientists of Dalton's time have that made it easier to accept Dalton's ideas? That's what we're going to find out in this WebQuest.
Your Task

Your task is to search for the evidence that supports Dalton's theory of atoms. In order to do this, you must know the four main principles of Dalton's atomic theory, which are listed below.

All matter is made of tiny particles, called atoms.

Atoms are neither created nor destroyed in chemical reactions.

Atoms of different elements combine in whole number ratios, with more than one ratio being possible for a given combination of elements.

Each element is made of a different kind of atom, and the atoms of different elements have different masses.

The Process

You are going to prepare a report that describes how Dalton arrived at these four conclusions. Your report should include answers to all the questions listed below. Note: by searching for the answers to these questions, you will find all the evidence necessary to complete this project.

a. What is the law of conservation of mass? (8 points)

b. Who developed it? (4 points)

c. Describe the experiments this person carried out that led to the law's formulation.
(8 points)

d. Which of Dalton's four principles does it support, and how does it support it?
(8 points)

a. What is the law of definite proportions? (8 points)

b. Who developed it? (4 points)

c. Describe the experiments this person carried out that led to the law's formulation.
(8 points)

a. What is the law of multiple proportions? (8 points)

b. How is it different from the law of definite proportions? (8 points)

c. Who developed it? (4 points)

d. What experimental evidence led to the law's formulation?
(8 points)

e. Which of Dalton's four principles does it support, and how does it support it?
(8 points)

1 g of hydrogen will react with 19 g of fluorine to form HF. By contrast, 1 g of hydrogen will react with 80 g of bromine to form HBr.

a. How many grams of each product will form in each reaction? (4 points)

b. Why are different amounts of each element required to react with the same
amount of hydrogen? (4 points)

c. Which of Dalton's four principles does this observation support, and how does
it support it? (8 points)

Resources

Here are a few websites to help you begin your quest. Remember, these are just starting places. Feel free to make use of any additional resources, electronic or print, in your search for answers. Keep in mind that general references, such as your library's encyclopedia, can be useful as well.

Atoms

Dalton's Atomic Theory—from "General Chemistry Online!"—created by Fred Senese at Frostburg State University.

Elements and Atoms: Case Studies in the Development of Chemistry—part of Carmen Giunta's Classic Chemistry at Le Moyne College.

John Dalton—part of Chemical Achievers, from the Chemical Heritage Foundation.

My Brother, John—a fictionalized account as might have been penned by Dalton's brother, written by Judy Moody and Bette Bridges for the Woodrow Wilson Leadership Program in Chemistry.

Researches on Copper and Sur les mines de cobalt, nickel et autres—two papers by Joseph-Louis Proust, hosted by Carmen Giunta's Classic Chemistry from Le Moyne College.

Evaluation

Your report should answer all the questions listed in the Process section. To make things fair, everyone's report will be graded using a standard grading system, applying the point values listed next to each question.

Conclusion

After completing the WebQuest, we hope you will understand just how Dalton arrived at each of the four principles of his atomic theory. More importantly, you should learn how scientific theories are developed by observing and drawing conclusions based on observation. All theories, not just atomic theory, must be based on observation and must account for all observed facts. If not, they can't really be accepted as scientific theories. This role of observed evidence as the final judge of a theory's validity is the fundamental basis of science.

This CHF Chemistry WebQuest was created by Mark Michalovic.