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Chemistry 4.1
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4.1
Defining the Atom
The lab technician shown
here is using a magnifying
lens to examine a bacterial
culture in a petri dish. When
scientists cannot see the
details of what they study,
they try to obtain
experimental data that help
fill in the picture.
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© Copyright Pearson Prentice Hall
4.1
Defining the Atom
> Early Models of the Atom
Early Models of the Atom
• An atom is the smallest particle of an element
that retains its identity in a chemical reaction.
• Philosophers and scientists have proposed
many ideas on the structure of atoms.
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4.1
Defining the Atom
> Early Models of the Atom
Democritus’s Atomic Philosophy
How did Democritus describe atoms?
Democritus
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© Copyright Pearson Prentice Hall
4.1
Defining the Atom
> Early Models of the Atom
Democritus believed that atoms were
indivisible and indestructible.
Democritus’s ideas were limited because
they didn’t explain chemical behavior and
they lacked experimental support.
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4.1
Defining the Atom
> Early Models of the Atom
Dalton’s Atomic Theory
How did John Dalton further
Democritus’s ideas on atoms?
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4.1
Defining the Atom
> Early Models of the Atom
By using experimental methods, Dalton
transformed Democritus’s ideas on atoms
into a scientific theory.
The result was Dalton’s atomic theory.
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4.1
Defining the Atom
> Early Models of the Atom
All elements are composed of tiny indivisible
particles called atoms.
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4.1
Defining the Atom
> Early Models of the Atom
Atoms of the same element are identical. The
atoms of any one element are different from
those of any other element.
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4.1
Defining the Atom
> Early Models of the Atom
Atoms of different elements can physically mix
together or can chemically combine in simple
whole-number ratios to form compounds.
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4.1
Defining the Atom
> Early Models of the Atom
Chemical reactions occur when atoms are
separated, joined, or rearranged. Atoms of one
element are never changed into atoms of
another element in a chemical reaction.
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4.1
Defining the Atom
> Sizing up the Atom
Sizing up the Atom
What instruments are used to observe
individual atoms?
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4.1
Defining the Atom
> Sizing up the Atom
Despite their small size, individual atoms
are observable with instruments such as
scanning tunneling microscopes.
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Defining the Atom
> Sizing up the Atom
Iron Atoms Seen Through a Scanning
Tunneling Microscope
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