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10/8/13
4.1 Defining the Atom >
4.1 Defining the Atom > Sizing up the Atom
Chapter 4
Atomic Structure
4.1 Defining the Atom
4.2 Structure of the Nuclear Atom
4.3 Distinguishing Among Atoms
If you grind a piece of copper
into dust, each speck of red
dust would still have the
properties of copper.
•  If you could continue to make the
dust particles smaller, you would
eventually come upon a particle that
could no longer be divided and still
have the chemical properties of
copper.
•  This final particle is an atom.
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4.1 Defining the Atom > Early Models of the Atom
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4.1 Defining the Atom > Early Models of the Atom
How do you study something that you
cannot see it?
•  Atom
•  smallest particle of an element that has
the properties of that element
Early Models of the Atom
How did the concept of the atom
change from the time of Democritus
to the time of John Dalton?
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4.1 Defining the Atom > Early Models of the Atom
Democritus
– Greek philosopher (460 BC
–370 BC)
– One of the first to suggest
existence of atoms.
– Reasoned that atoms were
indivisible and
indestructible
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•  Early philosophers and scientists could
not see individual atoms
•  They still proposed ideas about the
structure of atoms.
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4.1 Defining the Atom > Early Models of the Atom
Democritus’s Atomic Philosophy
•  Democritus’s ideas did not explain
chemical behavior
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•  Lacked experimental support
•  Not based on the scientific method
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4.1 Defining the Atom > Early Models of the Atom
Dalton’s Atomic Theory
•  English chemist and school
teacher
•  Used experimental
methods, transformed
Democritus’s ideas into a
theory
•  Studied ratios in which
elements combine in
chemical reactions
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Dalton’s Atomic Theory
1.  All elements are
composed of tiny
indivisible particles
called atoms.
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4.1 Defining the Atom > Early Models of the Atom
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4.1 Defining the Atom > Early Models of the Atom
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4.1 Defining the Atom > Early Models of the Atom
Dalton’s Atomic Theory
2.  Atoms of the same
element are identical;
but atoms of one
element are different
from those of another
element.
3.  Atoms of different
elements can
combine in simple
whole-number ratios
to form compounds.
Atoms of
element B
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4.1 Defining the Atom > Early Models of the Atom
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4.  Chemical reactions occur
when atoms are separated,
joined, or rearranged in
different combinations.
Atoms of one element are
never changed into atoms of
another element.
Mixture of atoms of
elements A and B
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4.1 Defining the Atom >
Dalton’s Atomic Theory
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Dalton’s Atomic Theory
Atoms of
element A
Atoms of
element A
CHEMISTRY
& YOU
How was John Dalton able to study
atoms even though he couldn’t observe
them directly? What evidence did he use
to formulate his atomic theory?
Compound made by
chemically combining
atoms of elements A
and B
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10/8/13
4.1 Defining the Atom >
4.1 Defining the Atom > Sizing up the Atom
How was Democritus’s idea of the
atom different from Dalton’s?
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4.1 Defining the Atom > Sizing up the Atom
Sizing up the Atom
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4.1 Defining the Atom > Sizing up the Atom
•  Despite their small size, individual
atoms are observable with scanning
electron microscopes (SEM).
Atoms are very small.
•  A pure copper coin the size of a
penny contains about 2.4 x 1022
atoms.
•  In an SEM, a beam of e- is focused on the
sample.
•  By comparison, Earth’s population
is only about 7 x 109 people.
•  Electron microscopes are capable of much
higher magnifications than regular light
microscopes.
•  If you could line up 100,000,000
copper atoms side by side, they
would produce a line only 1 cm long!
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4.1 Defining the Atom >
If an atom has a radius of 1 x 10-10 m,
how many of these atoms must be
lined up in a row to produce a line
1 m long?
1 x 1010 (10,000,000,000) atoms of
radius 1 x 10-10 m would need to be lined
up in a row to produce a line 1 m long.
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