The Atom: A Philosophical Idea

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The Atom A Philosophical Idea

• The idea of atoms is very old.
• Democritus (Greek, 400 BC) - said that things
  were made up of tiny, indivisible particles
  (atoms) only an idea
• Aristotle - disagreed with Democritus idea his
  opinion more popular.
• No evidence to support either idea.

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Three Fundamental Laws of Chemistry

• Law of Conservation of Mass (1789)
• In ordinary chemical reactions, mass is neither
  created nor destroyed.
• Mass of the reactants equals the mass of the
  products.
• Law of Definite Proportions (1797)
• A chemical compound contains the same elements in
  exactly the same proportions regardless of the
  size of the sample or source of the compound.
• Example water hydrogen to oxygen
  ratio is always 2 to 1.

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• Law of Multiple Proportions (1803)
• if two or more different compounds are composed
  of the same two elements, then the proportions
  can be expressed as simple, whole-number ratios.
• Example
• Carbon and Oxygen
• Carbon monoxide - CO
• Carbon dioxide CO2

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John Dalton (1808)

• English school teacher, wanted to explain the
  laws of conservation of mass, definite
  proportions and multiple proportions.
• His model is called the Atomic Theory.

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• Postulates of his theory
• All matter is composed of extremely small
  particles called atoms.
• Atoms of a given element are identical in size,
  mass, and other properties atoms of different
  elements differ in size, mass, and other
  properties.
• Atoms cannot be subdivided, created, or
  destroyed.
• Atoms of different elements combine in simple
  whole-number ratios to form chemical compounds.
• In chemical reactions, atoms are combined,
  separated, or rearranged.

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• Some aspects of Daltons atomic theory have been
  revised. We now know that
• Atoms are divisible into even smaller particles.
• A given element can have atoms with different
  masses.

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One Minute Paper

• You have one minute to answer these two questions
  concerning todays lesson.
• What was the most important thing you learned?
• What is still muddy?