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Chapter 4
The structure of the atom
EARLY IDEAS ABOUT
MATTER…
SECTION 4-1
The Atom…
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Imagine you have a piece of aluminum
foil… and you cut it in half…
Would you ever finish this task? Or could
you forever divide aluminum into
smaller and smaller pieces??
Early ideas about Matter
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Ancient Greek Philosophers
– Democritus – “atomos” was the
smallest part of matter
– NOT infinitely divisible
Democritus vs. Aristotle
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Aristotle did NOT agree with
Democritus
Matter is made up of fire, water, air,
and earth NOT small particles
Because Aristotle was more famous,
people believed him
WHO WOULD YOU
BELIEVE? WHY?
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Asking people to believe either theory
was like asking someone to believe in
Santa Claus
Without scientific evidence… how can
we know something exists without
seeing it??
Take 2 minutes to write down what
theory you would believe and why…
Alchemy for 2000 years
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Aristotle believed
that any substance
could be
transmuted
(transformed) into
any other
substance simply by
changing the
relative proportions
of the 4 basic
qualities.
7
Alchemy for
2000 years

Alchemists were searching
for the evolution from
ignorance to
enlightenment.
– elixir of life
– philosopher’s stone
– the aqua vitae
– the panacea
8
John Dalton (1766-1844)
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He revived Democritus’s ideas
Performed SEVERAL chemical
reactions to develop his theory
Dalton’s Atomic Theory
4 Major Ideas…
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1. Matter is composed of small
indivisible and indestructible
particles called ATOMS
2. Atoms of a given element are
identical in size, mass and
chemical property
Dalton’s Atomic Theory
http://www.youtube.com/watch?v=HFF-2wyyTKc
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3. Different atoms combine in
simple whole-number ratios to
form compounds.
4. In a chemical reaction atoms
are NEVER created or destroyed,
only rearranged.
John Dalton (1766-1844)


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He developed a system of
symbols for each known
element.
His symbols were round to
model the tiny round atoms he
was theorizing about
Today we have changed to
the lettering system.
12
Law of Conservation of
Mass
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Dalton’s theory supports the law
of conservation of mass.
Atoms cannot be created of
destroyed, so mass remains the
same throughout the reaction.
ANSWER THE FOLLOWING
QUESTIONS…
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What does the law of conservation of
mass state?
How are the LAW OF CONSERVATION
OF MASS and the FOURTH idea of
Dalton’s theory related?
Homework
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Read Section 4.1
Pg 105, # 1-5