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Atomic Theory
Early ideas about matter -
Aristotle
believed matter was made of different combinations of earth, air, fire, and water.
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2. Development of Atomic Theory I
John Dalton
( )
matter is made of small, hard spheres that are different for different
elements
the smallest particle of an element is called an atom
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Atomic Theory II
J. J. Thomson
( )
atoms are made of smaller particles. He proposed the “raisin bun” model of the atom.
A positively charged bun with negatively charged particles spread out in it like raisins.
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Atomic Theory III
Ernest Rutherford
( )
atom contained a tiny dense centre called a nucleus, and electrons moved around the nucleus.
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Atomic Theory IV
Niels Bohr
( )
electrons surround
the nucleus in specific
“energy levels” or “shells.”
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Inside the Atom
An atom is the smallest particle of an element that retains the properties of the element.
All atoms are made up of three kinds of particles called subatomic particles. These particles are:
electrons
protons
neutrons
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