Chapter 4 Sec. 1

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Chapter 4 Sec. 1

• Studying Atoms

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Ancient Greek Atoms

• 2500 years ago, Democritus believe that all
  matter consisted of extremly small particles that
  couldnt be divided
• Four Elements
• Air, Water, Fire, Earth
• Water round and smooth
• Earth rough and prickley
• Greek Word atomos meaning uncut

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Ancient Greek Atoms

• Aristotle believed that there wasnt a limit to
  the number of times that an atom could be divided
• The model shown is Aristotles model to describe
  matter

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Daltons Atomic Theory

• Reintroduces the study of atoms by 1800s
• Evidence
• Mass of combined elements that combine when
  compounds form
• Formed ratios

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Daltons Atomic Theory

• Daltons Theory
• 1) Elements composed of atoms
• 2) Atoms of same element are alike
• 3) Atoms of different elements differ
• 4) Compounds are formed by joining atoms of two
  or more different elements in the same way

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Daltons Model
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Thomsons Model

• When objects rub, they gain ability to repel or
  attract
• Experiment used a glow beam in a tube with
  charged plates
• Beam was repelled by (-) and attracted by ()

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Thomsons Model

• 1904 English physicist introduced the idea of
  negatively charged particles known as electrons
• He thought electrons were embedded into the atom
• Plum Pudding Model

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Rutherfords Atomic Theory

• Almost all mass of the atoms were concentrated in
  the center called alpha particles
• Asked student to conduct experiment (Marsden)
• Rutherford predicted particles to go straight
  through
• But..

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• Gold Foil Experiment
• Shot a narrow beam of alpha particles at a gold
  foil
• Alpha particles scattered instead
• Reflecting off the positive nucleus

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Nucleus

• B/c of gold foil experiment, brought up idea of a
  nucleus
• Dense and positively charged