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Chapter 3
Atoms: The Building Blocks of Matter
Table of Contents
Section 1 The Atom: From Philosophical Idea to
Scientific Theory
Section 2 The Structure of the Atom
Section 3 Counting Atoms
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Copyright © by Holt, Rinehart and Winston. All rights reserved.
Chapter 3
Section 1 The Atom: From
Philosophical Idea to Scientific Theory
Objectives
• Explain the law of conservation of mass, the law of
definite proportions, and the law of multiple
proportions.
• Summarize the five essential points of Dalton’s
atomic theory.
• Explain the relationship between Dalton’s atomic
theory and the law of conservation of mass, the law
of definite proportions, and the law of multiple
proportions.
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Copyright © by Holt, Rinehart and Winston. All rights reserved.
Development of the atomic theory
 The search for a description of matter began with the
Greek philosopher Democritus more than 2000 years
ago.
 He and many other philosophers had puzzled over this
question:
Could matter be divided into smaller and smaller
pieces forever, or was there a limit to the number of
times a piece of matter could be divided? In other
words, is matter continuous or discontinuous?
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Copyright © by Holt, Rinehart and Winston. All rights reserved.
Developing the atomic theory
 Democritus concluded that matter could not be divided
into smaller and smaller pieces forever. Eventually the
smallest possible piece would be obtained.
 Democritus named this small, indivisible piece, an
atom; atom comes from the Greek word atomos, which
means “not to be cut” or “indivisible.”
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Developing the atomic theory
 Aristotle was part of the generation that succeeded
Democritus.
 Aristotle did not believe in atoms, instead, he thought
that all matter was continuous. His opinion was
accepted for nearly 2000 years
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Developing the atomic theory
 In the early 1800’s, the English chemist John Dalton
performed a number of experiments that eventually led
to the acceptance of the idea of atoms.
 In 1803, Dalton combined the results of his experiments
with other observations about matter and proposed an
atomic theory.
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Chapter 3
Section 1 The Atom: From
Philosophical Idea to Scientific Theory
Foundations of Atomic Theory
• The transformation of a substance or substances
into one or more new substances is known as a
chemical reaction.
• Law of conservation of mass: mass is neither
created nor destroyed during ordinary chemical
reactions or physical changes
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Copyright © by Holt, Rinehart and Winston. All rights reserved.
Chapter 3
Section 1 The Atom: From
Philosophical Idea to Scientific Theory
Foundations of Atomic Theory, continued
• Law of definite proportions: a chemical compound
contains the same elements in exactly the same
proportions by mass regardless of the size of the
sample or source of the compound
• Law of multiple proportions: if two or more different
compounds are composed of the same two elements,
then the ratio of the masses of the second element
combined with a certain mass of the first element is
always a ratio of small whole numbers
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Copyright © by Holt, Rinehart and Winston. All rights reserved.
Chapter 3
Section 1 The Atom: From
Philosophical Idea to Scientific Theory
Law of
Conservation of
Mass
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Copyright © by Holt, Rinehart and Winston. All rights reserved.
Chapter 3
Section 1 The Atom: From
Philosophical Idea to Scientific Theory
Law of Multiple Proportions
Chapter menu
Resources
Copyright © by Holt, Rinehart and Winston. All rights reserved.
Chapter 3
Section 1 The Atom: From
Philosophical Idea to Scientific Theory
Dalton’s Atomic Theory
• All matter is composed of extremely small particles
called atoms.
• Atoms of a given element are identical in size, mass,
and other properties; atoms of different elements
differ in size, mass, and other properties.
• Atoms cannot be subdivided, created, or destroyed.
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Copyright © by Holt, Rinehart and Winston. All rights reserved.
Chapter 3
Section 1 The Atom: From
Philosophical Idea to Scientific Theory
Dalton’s Atomic Theory, continued
• Atoms of different elements combine in simple wholenumber ratios to form chemical compounds.
• In chemical reaction, atoms are combined,
separated, or rearranged.
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Copyright © by Holt, Rinehart and Winston. All rights reserved.
Chapter 3
Section 1 The Atom: From
Philosophical Idea to Scientific Theory
Modern Atomic Theory
• Not all aspects of Dalton’s atomic theory have proven
to be correct. We now know that:
• Atoms are divisible into even smaller particles.
• A given element can have atoms with different
masses.
• Some important concepts remain unchanged.
• All matter is composed of atoms.
• Atoms of any one element differ in properties from
atoms of another element.
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Copyright © by Holt, Rinehart and Winston. All rights reserved.