Atomic Theory

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AtomicTheory

• A Brief History

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Democritus(circa. 400 B.C.)

• Matter is made of empty space and tiny particles
  called atoms.
• Atoms are indivisible.
• There are different types of atoms for each
  material in the world.

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Western PhilosophyPre-Socratic philosophy Western PhilosophyPre-Socratic philosophy
Democritus Democritus
Full name Democritus
Born ca. 460 BCEAbdera
Died ca. 370 BCE
School/tradition Pre-Socratic philosophy
Main interests metaphysics / mathematics / astronomy
Notable ideas atomism, distant star theory
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Aristotle(circa. 400 B.C.)

• Matter is not made of particles, but rather is
  continuous.
• Matter is made of earth, air, fire, and water.

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Western philosophyAncient philosophy Western philosophyAncient philosophy
Marble bust of Aristotle. Roman copy after a Greek bronze original by Lysippus c. 330 BC. The alabaster mantle is modern Marble bust of Aristotle. Roman copy after a Greek bronze original by Lysippus c. 330 BC. The alabaster mantle is modern
Full name ???st?t????, Aristotéles
Born 384 BCEStageira, Chalcidice
Died 322 BCEEuboea
School/tradition Peripatetic schoolAristotelianism
Main interests Physics, Metaphysics, Poetry, Theatre, Music, Rhetoric, Politics, Government, Ethics, Biology, Zoology
Notable ideas Golden mean, Reason, Logic, Passion
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Why was Democritus Ignored?
Because the early Greek philosophers did not
experiment and because Aristotle was an
established teacher.
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John Dalton(early 1800s)

• Matter consists of tiny particles called atoms
  which are indivisible and indestructible.
• All atoms of a particular element are identical.
• Each element has different atoms.
• Atoms combine in whole number ratios to form
  compound atoms.
• In chemical reactions, atoms are combined,
  separated, or rearranged but are never created,
  destroyed, or changed.

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Why were Daltons views accepted?

• The scientific method is now the proper way to
  do science.
• Daltons theory was based on experimental
  observations the law of Conservation of Mass and
  the law of Definite Proportions.
• Daltons theory correctly predicted the outcome
  of future experiments. These predictions became
  the law of Multiple Proportions.

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The following statements match principles of
Daltons theory. List the principle that explains
each statement.

1. When methane burns, it combines with oxygen in
   the air to form molecules of water and carbon
   dioxide.
2. Matter can never really be thrown away. That is
   one reason that recycling is important.
3. The formula for ethanol is C2H6O, and the formula
   for acetic acid in vinegar is C2H4O2.
4. Zinc is a softer metal than iron, and it reacts
   more readily with acid than iron does.
5. There is no difference between copper found in an
   ancient Mayan necklace and copper wire freshly
   made from copper ore.

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J.J. Thomson (late 1890s)

• Plum Pudding Model!
• All atoms contain negatively charged particles
  called electrons.
• All electrons are alike.
• Electrons exist in a pudding of positive
  charge.

Problem Required too many electrons!
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Robert Milliken(early 1900s)

• Oil Drop Experiment
• Determined
• Quantity of negative charge of the electron
• The charge to mass ratio of the electron
• Produced small droplets of negatively charged oil
  between to charged plates.
• The droplets could be suspended by apply a
  certain charge to the plates.

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Lord Rutherford(early 1900s)

• Each atom has a very tiny nucleus.
• The nucleus is positively charged.
• The electrons travel around the nucleus.
• The atom is mostly empty space.
• How
• Sent alpha particles through a thin sheet of gold
• Expected to pass right through, instead some were
  deflected at great angles

Problem Electrons should spiral into the nucleus.
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Neils Bohr(early 1900s)

• Atom contains positive nucleus.
• Electrons travel around the nucleus in specific
  energy levels.
• Electrons do not radiate energy in their normal
  energy level called the ground state.
• Electrons absorb energy and move to energy levels
  further from the nucleus called excited states.
• Electrons lose energy (light) as they return to
  lower energy levels.

Problem Model only works for hydrogen.
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The Bohr Atom
Light
Excited States
-

Ground State
Nucleus
Independent Practice Read pages 107-112 Complete
the Atomic Structure Multiple Choice worksheet
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