Atomic Model Theory
Atomic Theory Review
Take notice of scientists. It may
come in handy soon!
Honors Only
•Early Greek Models
Who was right?
Aristotle was wrong. However, his theory persisted for 2000
years.
DEMOCRITUS (400 B.C.)
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Thought matter could not be
divided indefinitely
Led to the idea of atoms in a
void
ARISTOTLE (350 B.C)
•
Modified an earlier theory
that matter was made of four
“elements”: earth, fire, water,
air
•John Dalton (1766 – 1844)
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•
“Billiard Ball” Model
1800 – proposed a modern atomic model based on
experimentation, not on pure reason
•
Performed a number of experiments that eventually led to the
acceptance of the idea of the atoms in 1803
•
Postulates
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All matter is made of atoms.
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Atoms of an element are identical.
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Each atom has different atoms.
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Atoms of different elements combine in constant ratios to form
compounds.
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Atoms are rearranged in reactions.
His ideas account for the law of conservation of mass.
•JJ Thomson (1856 – 1940)
“Plum Pudding” or “Cookie Dough” Model
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•
Discovered the electron
in 1897
Atoms were made from
a positively charged
substance with a
negatively charged
substance scattered
about, like raisin in a
pudding or chips in a
chocolate chip cookie.
•Ernest Rutherford (1871 – 1937)
Gold Foil Experiment
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Atoms mostly empty
space and not filled with
a positively charged
material
Small positive charged
center (nucleus)
Negatively charged
particles around the
nucleus
•Neils Bohr (1885 – 1962)
Planetary Model
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•
Found that electrons
move in definite orbits or
energy levels around the
nucleus in 1913
Electrons orbit the
nucleus in “shells”.
•Electron Cloud Model
Current Model
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Describes a cloud-like
region where the electron
is likely to be found
Can not say with certainty,
where the electron
actually is at any point in
time, yet can describe
where it ought to be
Cloud represents a history
where the electron has
probably been and where
it is likely to be going