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: