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Development of the atomic theory (8th)
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INTRODUCION to ATOMSIgnacio Anguera de Sojo
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DEVELOPMENT OF THE ATOMIC
THEORY
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1.- Early Ideas (~ 2500 years ago)• Democritus (~ 4th century B.C.)
• “Pre-atomic” theory: atoms where “uncuttable”
Atom = “not able to divide”
DEVELOPMENT OF THE ATOMIC THEORY
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1.- Early Ideas (~ 2500 years ago)
DEVELOPMENT OF THE ATOMIC THEORY
•However, the much more popular Aristotle said…
• Democritus (~ 4th century B.C.)• “Pre-atomic” theory: atoms where “uncuttable”
Atom = “not able to divide”
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2.- Dalton’s theory
• Dalton’s model (1808)o Matter consist of indivisible atomso Atoms arrange in different combinations to make compounds
DEVELOPMENT OF THE ATOMIC THEORY
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2.- Dalton’s theory
• Dalton’s model (1808)o Matter consist of indivisible atomso Atoms arrange in different combinations to make compounds
•Experimentation: law of conservation of mass
Same proportions of Hydrogen and Oxygen produce the same proportions of water
DEVELOPMENT OF THE ATOMIC THEORY
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3.- Plum Pudding Model
• Thompson’s model (1808)o Atoms are divisible: Discover electrons
DEVELOPMENT OF THE ATOMIC THEORY
Plum Pudding Model
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3.- Rutherford's model
• Gold foil experiment or the Rutherford experiment
DEVELOPMENT OF THE ATOMIC THEORY
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3.- Rutherford's model
• What Rutherford expected:
DEVELOPMENT OF THE ATOMIC THEORY
Helium ions with a positive charge
According to Thompson’s model, Rutherford thought that particles will pass through the uniform positively charge sphere with little or non defalcation
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3.- Rutherford's model
• What Rutherford found:
DEVELOPMENT OF THE ATOMIC THEORY
Majority of particles penetrated the foil (without deflection or with slight deflection). However a very small % of particles were deflected through angles much larger than 90 degrees or even scattered back toward the source.
Helium ions with a positive charge (α-particles)
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3.- Rutherford's model
• What Rutherford proposed : the atom contained a very physically-small (as compared with the size of the atom) positive charge, which could repel the alpha particles if they came close enough.
DEVELOPMENT OF THE ATOMIC THEORY
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4.- Bohr’s Model
• Niels Bohr (1913): electrons are not randomly. They move in certain paths (orbital or energy levels)
DEVELOPMENT OF THE ATOMIC THEORY
like planets around the sun
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5.- Modern Atomic Theory: Quantum Model• Schrodinger discover that electrons don’t move in exact
paths. They are in –electron clouds-.
DEVELOPMENT OF THE ATOMIC THEORY
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DEVELOPMENT OF THE ATOMIC THEORY
Summary:
