development of the atomic theory chapter 6 section 1
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Development of the Atomic Theory
Chapter 6 Section 1
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The Beginning of Atomic Theory
• An atom is the smallest particle an element can be divided into and still have the properties of that element.
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Ancient Greece• Around 440 B.C., Democritus
proposed that matter is made up of “uncuttable” particles which are always moving.
• He called the particle an atom.
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Dalton’s Atomic Theory• All substances are made of
atoms. Atoms are small particles that cannot be created, divided, or destroyed.
• Atoms of the same elements are exactly alike, but different from other elements.
• Atoms join with other atoms to make new substances.
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Thomson’s Discovery of Electrons
• He discovered there are small particles inside the atom and that atoms can be divided.
• He discovered that some particles had a negative charge called electrons.
• He didn’t know how they were arranged, but thought they might look like chocolate-chip ice cream.
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Cathode Ray Tube
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Rutherford’s Atomic
“Shooting Gallery”• He aimed a beam
of positively charged particles into gold foil.
• Most passed through, but some bounced back.
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The Nucleus & the Electrons
• Rutherford discovered that atoms are mostly empty space.
• He said atoms have a tightly packed center called a nucleus.
• He developed a new model of the atom.
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Bohr’s Electron Levels
•He studied the way atoms react to light.
•He suggested that electrons travel around the nucleus in definite paths.
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The Modern Atomic Theory• Schrodinger and Heisenberg showed
that electrons do not travel in definite paths.
• The exact path can not be predicted.
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ENERGY LEVELS• Each electron cloud
exists at a certain energy level.
• The energy of each electron keeps it in motion around the nucleus of the atom.SILVER
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The Size of an Atom
• Atoms are very small, yet the atom was discovered without seeing a single atom.
• There are 20 thousand billion, billion atoms in a penny.
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OBSERVING ATOMS• Atoms are so small
that light waves are too large to be used to observe them.
• The tools that scientist now use to observe atoms include the electron microscope.
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End of Section 1
Electron Microscope image of
Silicon Nitrate
Video