EARLY MODELS
OF THE ATOM
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WHAT’S THE MATTER?
•Ancient civilizations have wondered what made up the stuff
around them.
•Some early ideas included natural elements like earth, air, fire and
water. (Empedocles)
•The
Greek
philosopher,
Democritus,
suggested that matter could be cut down
into smaller pieces until you reached a
single indivisible particle which he called
the atom.
•As history moved along, others would experiment
and observe to expand our knowledge of the
structure of the atom.
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DALTON’S ATOMIC THEORY
• John Dalton was a teacher that came up with his theory
of atomic structure based on the work of many scientists
of his era.
• Dalton’s theory (1803) included the following:
– Matter consists of definite particles called atoms.
– Each element has its own type of atom.
– Atoms of different elements have different properties.
– Atoms of two or more different elements can combine
in specific ratios to form compounds.
– Atoms cannot be created or destroyed or broken up in
a chemical change.
• Future scientists would build upon Dalton’s work to
help arrive at our current understanding of atomic
structure.
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THE SUBATOMIC PARTICLES
• The next scientist to assist in our understanding
of atomic structure was J.J. Thomson in 1897.
• Thomson used advances in technology to arrive
at his famous raisin bun model of the atom.
• He said atoms were like raisin buns in that you
had a positively charged sphere with negatively
charged particles called electrons – the “raisins”
– scattered throughout.
• This is kind of accurate if you think about what you
already know about the atom.
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RAISIN BUN 2.0
• In 1911, Ernest Rutherford conducted experiments
that furthered our understanding of atomic structure.
• He concluded that the atom had a nucleus that held
positive charges, which he named protons.
• This nucleus was surrounded by mostly empty
space which had negatively charged particles within
it.
• James Chadwick would suggest the
existence of neutrons within the nucleus of
the atom in 1932. The neutrons had the
same mass as a proton but did not carry a
charge.
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ATOMIC STRUCTURE
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THAT’S ALL FOLKS!
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