Fall 2016
Chapter 2
Atoms
Atoms: The Greek Idea
~384 B.C.E., Aristotle:
All matter is
composed of four
elements and all
matter is continuous,
not atomistic.
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Fall 2016
Atoms: The Greek Idea
Aristotle declared
matter to be infinitely
divisible.
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Atoms: The Greek Idea
~ 450 B.C.E., Leucippus and
Democritus
Atomos: The point at which matter can no
longer be subdivided.
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Fall 2016
Lavoisier: The Law of
Conservation of Mass
Early 1700s Lavoisier:
Law of Conservation of
Mass: During a chemical
change, matter is neither
created nor destroyed.
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Lavoisier: The Law of
Conservation of Mass
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Fall 2016
Proust: The Law of Definite
Proportions
1799, Proust:
Law of Definite Proportions: A compound
always contains the same elements in certain
definite proportions.
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Proust: The Law of Definite
Proportions
Regardless of the source, copper carbonate has
the same composition.
Malachite (mineral)
Cu(OH)2CO3
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Fall 2016
Proust: The Law of Definite
Proportions
The Berzelius experiment illustrates the Law of
Definite Proportions.
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John Dalton and the Atomic
Theory of Matter
1803, John Dalton:
Law of Multiple
Proportions: Elements
may combine in more
than one set of
proportions, with each
set corresponding to a
different compound.
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Fall 2016
John Dalton and the Atomic
Theory of Matter
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John Dalton and the Atomic
Theory of Matter
• All matter is composed of extremely small
particles called atoms.
• All atoms of a given element are alike and
differ from the atoms of any other element.
• Compounds are formed when atoms of
different elements combine in fixed
proportions.
• A chemical reaction involves the
rearrangement of atoms.
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Fall 2016
Out of Chaos: The Periodic
Table
1869, Dmitri Mendeleev
Mendeleev arranged the
elements in order of increasing
atomic mass. He left gaps for
yet undiscovered elements. He
also predicted the properties of
those elements. When those
elements were eventually
discovered, many of his
predictions were found to be
accurate.
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Out of Chaos: The Periodic
Table
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Fall 2016
Out of Chaos: The Periodic
Table
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Atoms: Real and Relevant
Atoms are a very real
concept. It is even
possible to observe
computer-enhanced
images of atoms.
Pt
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Fall 2016
Molecules
Molecules are groups of
atoms chemically bonded
together.
A molecule of water is
composed of two atoms
of hydrogen (H) bonded
to an atom of oxygen (O).
H2O
Henry Cavendish (1783):
electrolysis of water
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