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Chemistry 4.1
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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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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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Defining the Atom >
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Early Models of the Atom
Democritus’s Atomic Philosophy
How did Democritus describe atoms?
Democritus
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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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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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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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Defining the Atom > Early Models of the Atom
All elements are composed of tiny indivisible particles called atoms.
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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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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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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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Defining the Atom >
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Sizing up the Atom
Sizing up the Atom
What instruments are used to observe individual atoms?
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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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