Download Atomic Theory Timeline II

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ATOMIC THEORY
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Democritus Atom
 Democritus
is an Ancient Greek
philosopher born in Abdera,
Thrace, Greece
 He
was said to be the first step
toward the current atomic
theory.
 Hypothesized
that all matter is
composed of tiny indestructible
units, called atoms.
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His
atomic theory contradicted the idea
that matter can be infinitely divided.
According
forever.
to him, atoms cannot be divided
In
the long run, the object will become so
small and invisible that you cannot divide it
any further.
He
said that these indivisible invisible
particles are ATOMS. The word “atomos”
means not to be cut or indivisible.
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Aristotle
 384
A
to 322 B.C.
popular Greek Philosopher
 Disagreed
with Democritus ideas
 He
believed that you would never end up with
an indivisible particle.
 His
 He
ideas were proven incorrect.
had such a strong influence. So people
believed him and ignored Democritus.
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John Dalton
English,
chemist,
meteorologist and
physicist.
He
is best known for his
pioneering work in the
development of modern
atomic theory.
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5 POINTS of
Dalton’s Theory
 All
matter consists of tiny particles called
atoms. These are indivisible and
indestructible.
 All atoms of a given element are identical in
mass and properties.
 The atoms of a given element are different
from those of any other element; the atoms
of different elements can be distinguished
from one another by their respective
relative atomic weights.
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 Compounds
are formed by a
combination of two or more different
kinds of atoms.
 Compounds
are pure substances. They
can’t be separated into elements by
phase changes because the atoms of
different elements are bonded to one
another and are not easily separated
from one another.
A chemical reaction results to
rearrangement of atoms.
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Joseph John “JJ”
Thomson
•British physicist
•Discoverer of Electrons
•Discoverer of Isotopes
Isotopes have the same number of protons and
electrons, thus they have the same atomic
number and the same chemical reactions.
But they have different numbers of neutrons
giving them different atomic masses. Some
isotopes are heavier or lighter than others.
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Thomson’s Cathode-Ray Tube
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•Proposed the Plum pudding
model
•Awarded the 1906 Nobel Prize
in Physics
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PLUM PUDDING
MODEL
•Also known as the “Chocolate
Chip Cookie or Blueberry Muffin
Model.”
•Atom is composed of electrons
surrounded by a soup of positive
charge to balance the electron’s
negative charge, like negativelycharged “plums” surrounded by
positively-charged “pudding”.
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•Sometimes visualized as having a cloud of
positive charge, a striking contrast to the most
recent atomic model, which describes the
positive nucleus to be surrounded by an
electron cloud.
•Electrons were free to rotate within the cloud
of positive substance.
•These orbits were stabilized in the model by
the fact that when an electron moved farther
from the center of the positive cloud, it felt a
larger net positive inward force, because there
was more material of opposite charge, inside
its orbit.
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Ernest Rutherford
•New Zealand chemist and
physicist
•Father of Nuclear Physics
•Discovered that atoms have
their positive charge
concentrated in a very small
nucleus.
•Rutherford Model
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•Gold
Foil Experiment
•Discoverer of proton
•Awarded Nobel Prize in
Chemistry in 1908
•Widely credited as splitting the
atom in 1917
•Leading the first experiment to
“split the nucleus”
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Gold Foil
Experiment
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•The unexpected results of the
experiment demonstrated for the
first time the existence of the
atomic nucleus, leading to the
downfall of the plum pudding
model of the atom, and the
development of the Rutherford (or
planetary) model.
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Bohr’s Model
 Also
known as the
planetary model
 Neutrons
and protons are
in the nucleus while the
electrons are orbiting the
nucleus
 Electrons
are able to jump
from one orbit to another
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Electron Cloud
Model
 1920
 Consists
of a dense nucleus composed of
protons and neutrons surrounded by
electrons that exist in different clouds at
the various energy levels.
 Erwin
Schrodinger and Werner
Heisenburg developed probability
functions to determine the regions or
clouds in which electrons would most
likely be found.