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10/4/2015
The Indivisible
Unit 3: Atomic Structure - The Nucleus
Lesson 3.1: Early Ideas about Matter
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Lesson 3.1 Early Ideas About Matter
• Compare and contrast the atomic models of
Democritus, Aristotle, and Dalton.
p
the
• Understand how Dalton's theoryy explains
conservation of mass.
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Lesson 3.1 Early Ideas About Matter
Dalton’s Atomic Theory
The ancient Greeks tried to explain
matter, but the scientific study of
the atom began with John Dalton in
the early 1800's.
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What’s the Smallest Thing Around?
The atom:
From the greek “atomos”- “indivisible” =
Can’t be seen
1 gram of hydrogen gas:
60,200,000,000,000,000,000,000 atoms
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Greek Philosophers
• Many ancient scholars believed matter was
composed of such things as earth, water, air,
and fire.
• Many believed matter
could be endlessly
divided into smaller
and smaller pieces.
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Greek Philosophers
• Democritus (460–370 B.C.) was the first
person to propose the idea that matter was not
infinitely divisible, but made up of individual
particles called atomos.
• He believed that atoms were indivisible and
indestructible
• Aristotle (484–322 B.C.) disagreed with
Democritus because he did not believe empty
space could exist.
• Aristotle’s views went unchallenged for 2,000
years until science developed methods to test
the validity of his ideas.
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Greek Philosophers
• John Dalton revived the idea of the atom in the
early 1800s based on numerous chemical
reactions.
• Dalton’s atomic theory easily explained
conservation of mass in a reaction as the result
of the combination, separation, or
rearrangement of atoms.
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Dalton’s Atomic Theory
(experiment based!)
1) All elements are
composed of tiny
indivisible particles called
atoms
John Dalton
(1766 – 1844)
2) Atoms of the same
element are identical.
Atoms of any one element
are different from those of
any other element.
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Dalton’s Atomic Theory (Cont.)
3) Atoms of different elements
combine in simple whole-number
ratios to form chemical
compounds
4) In chemical reactions, atoms are
combined, separated, or
rearranged – but never changed
into atoms of another element.
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Section 3.1 Assessment
Who was the first person to propose the
idea that matter was not infinitely
divisible?
A.
B.
C.
D.
Aristotle
Plato
Dalton
Democritus
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Section 3.1 Assessment
Dalton’s theory also conveniently explained
what?
A.
B.
C.
D.
the electron
the nucleus
law of conservation of mass
law of Democritus
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