Transcript Evolution of the Atom

Evolution of the Atom
Evolution of Atomic Theory
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Evolution of the Atom
The Early History of Atomic Theory
Democritus/Leucippus (450 BC)
Matter is made up of indivisible particles
Called these particles “atomos”=indivisible
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Evolution of the Atom
Aristotle’s Composition Theory (354 BC)
The structure of DNA was determined in 1954.
How many years after Aristotle's idea is that?
The universe is made of matter and all
matter is composed of four elements.
Earth
Air
Fire
Water
Early thinkers looked for laws in science.
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Evolution of the Atom
What is a “Law” in science?
A “Law” in science is a concise
statement or mathematical
equation about a basic and
repeatable relationship in nature.
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Evolution of the Atom
What happen in American history in 1776?
Antoine Lavoisier (1776)
Law of Conservation of Mass
Mass is neither created nor destroyed (but this did
not always agree with experimental observations).
Later, Einstein showed that there is a connection
between mass and energy such that matter can
be converted to energy (and vise versa).
Einstein’s idea is expressed in the equation:
E = mc
2
Where c is the speed of light in meters/second.
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Evolution of the Atom
Antoine Lavoisier (1776)
Law of Conservation of Mass Example
Light bulb
Before a bulb burns out, the bulb
contains some inert gas molecules
and a metal filament.
After a bulb burns out, the bulb has a broken filament,
small amount of metal atoms deposited on the glass
inside the bulb, and the same amount of inert gas
molecules it had before.
The total mass of the system is not different.
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Evolution of the Atom
Antoine Lavoisier (1776)
Law of Conservation of Mass Example
Copper carbonate can ultimately be decomposed into its
elements. This illustrates the mass conservation law.
CuCO3  Cu + C + O2
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Evolution of the Atom
Antoine Lavoisier (1776)
Law of Conservation of Mass Example
copper carbonate decomposition reaction
Before the reaction, you have 103 grams of copper
carbonate.
After the complete reaction: you still have 103
grams of material but all of the copper carbonate
has disappeared.
The total mass of the system is unchanged:
mass before reaction = mass after reaction
103.0 g = 40.2 g+ 52.5 g + 10.3 g
CuCO3  Cu + C + O2
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Evolution of the Atom
Dalton’s Atomic Theory (1808)
The first atomic theory
Was Thomas Jefferson, James Monroe, or
James Madison president of the United
States in 1808?
• Each element is made up of tiny,
indivisible particles called atoms.
• Atoms of the same element are identical.
• (If the atoms are not the same, they are
not from the same element.)
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Evolution of the Atom
Dalton’s 1808 Atomic Theory (continued)
Chemical compounds are formed
when atoms combine with each other.
A given compound always has the same
relative numbers and types of atoms.
Is this a law?
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Evolution of the Atom
Dalton’s 1808 Atomic Theory (continued)
Chemical reactions involve reorganization
of atoms.
Atoms are not changed in chemical
reactions.
How are the different atoms held together?
Is this a law?
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Evolution of the Atom
Dalton’s 1808 Atomic Theory (continued)
Laws of chemical combination
led to a theory of the atom as
a solid indivisible sphere (i.e.,
a marble).
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Evolution of the Atom
J. J. Thomson’s “Plum Pudding” Model (1898)
What was the name of the U.S. battle ship
that sunk in 1898?
The atom is divisible
Thomson postulated the existence of electrons
based on experiments using cathode ray tubes.
The atom is a ball of
diffuse positive (+)
charge with small
negative (-) bits
throughout its volume.
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Evolution of the Atom
Thomson’s Experiment: Deflection of “Cathode
Rays” by an Applied
Electromagnet connected
Electric Field
to power supply
Electron beam
Electrical signal
detected only when
electrons collide
with this positive
plate
Negatively
charged
end cap
Electromagnet connected
to power supply
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Evolution of the Atom
Ernest Rutherford’s Model (1909)
•
Was New Mexico a state in the United
He postulated that an atom:
States in 1909?
•
has a dense positive (+) core that was called
the atom’s nucleus.
•
has several negative (-) particles called
electrons traveling around the nucleus at a
large distance from the nucleus.
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Evolution of the Atom
Rutherford’s Experiment: Deflection of “Alpha”
Particles by a Thin
Piece of Gold Foil
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Evolution of the Atom
Rutherford’s Experiment: Deflection of “Alpha”
Particles by a Thin
Piece of Gold Foil
Some of the alpha particles were reflected almost
straight back toward the emitter. Thomson’s model of
the atom could not explain why the alpha particles
would not simply pass through the foil all the time.
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Evolution of the Atom
Rutherford’s Experiment (continued)
This alpha particle
reflects back.
This alpha particle missed
the nucleus and did pass
through the gold foil.
Alpha
particles
emitted from
a radioactive
atom source
This alpha particle struck the nucleus
and was reflected to the side. It did
not pass through the gold foil.
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Evolution of the Atom
Thinking people tried to develop theories to help explain what they
observed. However, each new theory always left questions unanswered.
Democritus/Leucippus atomos theory (450 BC)
How do different things get made and big enough to see?
Aristotle’s composition theory (354 BC)
How did earth, air, water, and fire get
changed into trees, rocks, and living things?
Dalton’s atomic theory (1808)
Why do some of these indivisible particles (atoms)
join together and some do not?
J. J. Thomson’s “Plum Pudding” model (1898)
Why do some of the alpha particles pass through a
material when some of the particles do not?
Ernest Rutherford’s nucleus model (1909)
Why don’t the electrons eventually lose their energy
for motion and crash into the atom’s positive nucleus?
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Evolution of the Atom
Thinking people tried to develop theories to help explain what they
observed. However, each new theory always left questions unanswered.
As the models get better and better,
more observations are explained and the
questions to be answered get more
complicated.
?
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Evolution of the Atom
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