the development of modern atomic theory viewing the invisible v. anderson 2005—mergenthaler voc....
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The Development of Modern The Development of Modern Atomic TheoryAtomic Theory
Viewing the
Invisible
V. Anderson 2005—Mergenthaler Voc. Tech. High School
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Early Ideas!!Early Ideas!!
Early man, including the philosophers of Greece, believed that all matter was made of 4 basic “elements”
– Earth
– Water
– Air
– Fire
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New IdeasNew Ideas
As time progressed, a number of individuals contributed to the idea of the modern atom.
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DemocritusDemocritus
Lived: ancient GreeceBelieved: “According to convention, there
is a sweet and a bitter, a hot and a cold, and according to convention there is color. In truth there are atoms and a void.”
Coined the term Atom
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John DaltonJohn Dalton
Born: 1766, Cumberland, EnglandOccupation: TeacherBelieved: “We might as well attempt
to introduce a new planet into the solar system, or annihilate one already in existence, as to create or destroy a particle of Hydrogen.” --J. Dalton, A New System of
Chemical Philosophy, 1808
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Key Points of Dalton’s Atomic Key Points of Dalton’s Atomic TheoryTheory
Dalton's atomic theory rests on the following postulates.
1. All matter consists of tiny particles.(atoms)
2. Atoms are indestructible and unchangeable.
3. Elements are characterized by the mass of their atoms. All atoms of the same element are identical and different from atoms of other elements.
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JJ ThomsonJJ Thomson
Born: 1856Place: Manchester,
EnglandDiscovered ElectronsPlum pudding Model
– A unit made of multiple pieces
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Plum Pudding ModelPlum Pudding Model“I see the atom as being made of electricity. I call my picture the “plum pudding” model of an atom. Note that in this model negatively charged particle called electrons(the plums) are embedded in a sphere of positive charge(the pudding).”
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Thomson’s ExperimentThomson’s ExperimentThomson used a Vacuum tube (Cathode
Ray Tube) to demonstrate that the produced ray was made of charged particles.
The ray that was produced in the tube would bend toward a Positive Magnet and away from a Negative magnet, proving that the particles were Negatively charged.– ELECTRONS!!!!
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Thomson’s Experiment - Thomson’s Experiment - DiagramDiagram
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Cathode Ray TubeCathode Ray Tube
It may seem mundane and boring to us today, but to audiences at popular scientific lectures, the glow in this simple cathode tube was eerie, and to physicists it presented a challenging mystery.
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Ernest Rutherford’s AtomErnest Rutherford’s Atom
“I suggest that the atom has the following characteristics:”
A small core, or nucleus, that contains most of the mass of the atom.
The nucleus is made of particles called protons
The protons are surrounded by negatively charged electrons, but most of the atom is actually empty space.
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Ernest Rutherford and the Ernest Rutherford and the Structure of the AtomStructure of the Atom
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Rutherford’s observationsRutherford’s observations
Most particles passed through the gold foil without any effect.
A few particles passed through but were deflected to the side.
A few particles bounced back toward the source
He described these “bouncers” as cannon balls deflected by tissue paper.
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Neils BohrNeils Bohr
1913 Neils Bohr, a Danish scientists, developed a theory:– Electrons travel around
the nucleus in orbits like those of the planets around the sun
– “The Bohr Model”
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Development of the Modern Development of the Modern Atomic TheoryAtomic Theory
Solidparticle
ElectronsIn planetary Orbit around Nucleus
Nucleus Surrounded byA cloud of electronsIn energy levels