Atoms: the nature of things

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Chapter 2

• Atoms the nature of things

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Chapter 2 Atoms

• Greek Model of the Atom
• Sought to answer the question, What is matter?
• A Greek philosopher Leucippus and his student,
  Democritus, had the following thought experiment
• Take a piece of gold and cut it in half. Then
  cut one of the halves of gold in half again and
  so forth.

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Chapter 2 Atoms

• Greek Model of the Atom contd
• They wondered how long you could continue to cut
  the piece of gold in half.
• Do this process go on forever?
• What did they think?
• Is there some stopping point?
• Where does the word Atom come from?

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Chapter 2 Atoms

• Greek Model of the Atom contd
• Other philosophers, such as Plato and Aristotle,
  felt it was absurd to think that tiny individual
  particles were indivisible.
• For almost 2,000 years atomism was simply an
  endless discussion between scholars.
• Atomism is belief that matter is made up of tiny
  individual particles that are indivisible.

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Chapter 2 Atoms

• Atomic theory of Matter
• Definition
• Theory handed down to us from the Greeks.
• This useful idea explains a broad range of
  observations.

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Chapter 2 Atoms

• Experimental evidence
• John Dalton (1766-1844)
• Discovered that when certain substances combine
  to form other substances, they do so in simple
  ratios by weight.
• Example Water or H20 weight ration of H to O is
  2/16 or 1/8.
• He did most of his analysis with different types
  of gases, mainly C02, C0
• Published book, New System of Chemical
  Philosophy establishing the modern atomic theory

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Chapter 2 Atoms

• Experimental Evidence contd
• Robert Brown (same time as Dalton)
• Discovered that pollen grains erratically moved
  around when suspended in water. The discovery
  was made with the help of a microscope.
• This type of motion is referred to Brownian
  motion or random motion.

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Chapter 2

• Experimental Evidence contd
• Einstein (1905)
• Correctly calculated the time it would take dust
  grains to diffuse to bottom of a glass of water.
• After Einsteins work, scientists have not
  questioned the atomic theory.

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Chapter 2 Atoms

• Does all of the experimental evidence prove the
  atomic theory of matter?
• No!! Its possible that there is some other
  explanation for what is observed.
• What is important to note is that a general idea
  can be made more plausible by the amount of
  observations supporting that idea.

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Chapter 2 Atoms

• What other evidence supports the atomic theory of
  matter?

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Chapter 2 Atoms

• Modern view of matter
• The atomic theory of matter links macroscopic
  phenomena, I.e. what we see or sense, to
  phenomena at the unseen microscopic level.
• Scientists classify matter into three different
  states solid state, liquid state, and gas
  state.
• Microscopic perspective is helpful in
  understanding the three states of matter.

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Chapter 2 Atoms

• Solid State of Matter
• What kind of shape do solids have?
• Is the arrangement of atoms in a solid fixed or
  free?

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Chapter 2 Atoms

• Liquid State of Matter
• What kind of shape do liquids have?
• How does the shape of the container influence
  liquids?
• Are the atoms in a liquid free to move around?

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Chapter 2 Atoms

• Gas State of Matter
• Can gases be compressed?
• Other properties of a gas

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Chapter 2 Atoms

• Microscopic Interpretation of Warmth
• What happens to a substances when you heat it up?
• How about when you cool it down?

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Chapter 2 Atoms

• Microscopic Interpretation of Warmth
• Definition Temperature is associated with
  random (disorganized) microscopic motion that are
  not visible macroscopically.

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Chapter 2 Atoms

• Atomic Materialism
• The philosophy that only matter is real and that
  everything is determined by its impersonal
  workings.
• The Greek philosopher Democritus felt that atoms
  are all there is, reality is nothing more than
  our perception of the atoms around us.
• Do you agree?

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Chapter 2 Atoms

• Problem solving session
• Can you tell how many atoms are in a given a
  chemical formula?
• Examples H20, CH4, H2SO4
• Scientist tend to represent large and small
  numbers using notation called Powers of Ten.
• Be sure to know how to add, subtract, multiply,
  and divide numbers written in terms of Powers of
  Ten.