Transcript Document 7363281

Atomic
Theory
A Brief History
Democritus
(circa. 400 B.C.)
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Matter is made of empty space and tiny
particles called “atoms.”
Atoms are indivisible.
There are different types of atoms for
each material in the world.
Western Philosophy
Pre-Socratic philosophy
Democritus
Full name
Democritus
Born
ca. 460 BCE
Abdera
Died
ca. 370 BCE
School/tradition
Pre-Socratic philosophy
Main interests
metaphysics /
mathematics /
astronomy
Notable ideas
atomism, distant star
theory
Aristotle
(circa. 400 B.C.)
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Matter is not made of particles, but
rather is continuous.
Matter is made of earth, air, fire, and
water.
Western philosophy
Ancient philosophy
Marble bust of Aristotle. Roman copy after a
Greek bronze original by Lysippus c. 330 BC.
The alabaster mantle is modern
Ἀριστοτέλης,
Full name
Aristotélēs
Born
384 BCE
Stageira, Chalcidice
Died
322 BCE
Euboea
School/tradition
Main interests
Notable ideas
Peripatetic school
Aristotelianism
Physics, Metaphysics,
Poetry, Theatre, Music,
Rhetoric, Politics,
Government, Ethics,
Biology, Zoology
Golden mean, Reason,
Logic, Passion
Why was Democritus Ignored?
Because the early Greek philosophers
did not experiment and because
Aristotle was an established teacher.
John Dalton
(early 1800’s)
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Matter consists of tiny particles called atoms
which are indivisible and indestructible.
All atoms of a particular element are identical.
Each element has different atoms.
Atoms combine in whole number ratios to form
compound atoms.
In chemical reactions, atoms are combined,
separated, or rearranged but are never created,
destroyed, or changed.
Why were Dalton’s views accepted?
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The scientific method is now the proper way to
“do science.”
Dalton’s theory was based on experimental
observations: the law of Conservation of Mass
and the law of Definite Proportions.
Dalton’s theory correctly predicted the outcome
of future experiments. These predictions
became the law of Multiple Proportions.
The following statements match principles
of Dalton’s theory. List the principle that
explains each statement.
1.
2.
3.
4.
5.
When methane burns, it combines with
oxygen in the air to form molecules of water
and carbon dioxide.
Matter can never really be thrown away. That
is one reason that recycling is important.
The formula for ethanol is C2H6O, and the
formula for acetic acid in vinegar is C2H4O2.
Zinc is a softer metal than iron, and it reacts
more readily with acid than iron does.
There is no difference between copper found
in an ancient Mayan necklace and copper wire
freshly made from copper ore.
J.J. Thomson
(late 1890’s)
Plum Pudding Model!
All atoms contain negatively charged particles
called electrons.
 All electrons are alike.
 Electrons exist in a “pudding” of positive
charge.
Problem: Required too many electrons!
Robert Milliken
(early 1900’s)
Oil Drop Experiment
 Determined
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Quantity of negative charge of the electron
 The charge to mass ratio of the electron
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Produced small droplets of negatively
charged oil between to charged plates.
 The droplets could be suspended by apply
a certain charge to the plates.
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Lord Rutherford
(early 1900’s)
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Each atom has a very tiny nucleus.
The nucleus is positively charged.
The electrons travel around the nucleus.
The atom is mostly empty space.
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How
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Sent alpha particles through a thin sheet of
gold
Expected to pass right through, instead some
were deflected at great angles
Problem: Electrons should spiral into the nucleus.
Neils Bohr
(early 1900’s)
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Atom contains positive nucleus.
Electrons travel around the nucleus in specific
energy levels.
Electrons do not radiate energy in their normal
energy level called the ground state.
Electrons absorb energy and move to energy levels
further from the nucleus called excited states.
Electrons lose energy (light) as they return to
lower energy levels.
Problem: Model only works for hydrogen.
The Bohr Atom
Excited States
+
Nucleus
Ground
State
Independent Practice:
Read pages 107-112
Complete the Atomic Structure Multiple Choice worksheet