Transcript document

Developing an
Atomic Theory
Part I
The Greeks
Aristotle considered matter to
be “continuous,” that is, it
could be infinitely divided.
The Greeks
Democritus argued that all
matter was composed of
small, indestructible particles
called “atoms.”
The Greeks
Neither of these men were
experimentalists and could not show
any evidence to support their
hypotheses.
The Greeks
Neither of these men were
experimentalists and could not show
any evidence to support their
hypotheses.
However, Aristotle could at least argue
that matter looked continuous as we
sliced something (like cheese) thinner
and thinner.
John Dalton
John Dalton
He studied the results of
chemical experimentation.
John Dalton
He studied the results of
chemical experimentation.
The Law of Multiple Proportions
John Dalton
He studied the results of
chemical experimentation.
The Law of Multiple Proportions
“Whenever the same two
elements form more than one
compound, the different masses
of one element that combine with
the same mass of the other
element are in the ratio of small
whole numbers.”
John Dalton
He studied the results of
chemical experimentation.
The Law of Multiple Proportions
For example:1 g of C
combines with 1.333 g of O to
make carbon monoxide.
1 g of C combines with 2.667
g of O to make carbon
dioxide.
The ratio of O is 1:2
John Dalton
He studied the results of
chemical experimentation.
The Law of Definite Proportions
John Dalton
He studied the results of
chemical experimentation.
The Law of Definite Proportions
“In samples of any chemical
compound, the masses of the
elements are always in the same
proportions.”
John Dalton
He studied the results of
chemical experimentation.
The Law of Definite Proportions
For example:In 100 g of
water, there are 11.11 g of H
and 88.89 g of O, an H:O
ratio of 1:8.
In 425 g of water, there are
47.22 g of H and 377.78 g of
O, an H:O ratio of 1:8
John Dalton
He arrived at his own atomic
theory.
John Dalton
He arrived at his own atomic
theory.
The theory described how atoms
act.
John Dalton
He arrived at his own atomic
theory.
The theory described how atoms
act.
It did not describe the structure
of the atom.
John Dalton
Dalton’s Atomic Theory.
John Dalton
Dalton’s Atomic Theory.
All elements are composed of tiny
indivisible particles called atoms.
John Dalton
Dalton’s Atomic Theory.
All elements are composed of tiny
indivisible particles called atoms.
Atoms of the same element are
identical and the atoms of any one
element are different from the
atoms of any other element.
John Dalton
Dalton’s Atomic Theory.
Atoms of different elements can
physically mix together or can
chemically combine in simple wholenumber ratios to form compounds.
John Dalton
Dalton’s Atomic Theory.
Atoms of different elements can
physically mix together or can
chemically combine in simple wholenumber ratios to form compounds.
Chemical reactions occur when
atoms are separated, joined, or
rearranged. Atoms of one element,
however, are never changed into
atoms of another element as a result
of a chemical reaction.
J. J. Thomson
J. J. Thomson
Thomson discovered that the
atom was not a solid sphere.
J. J. Thomson
Thomson discovered that the
atom was not a solid sphere.
He used a cathode ray tube to show
the that atoms were (at least
partially) composed of negatively
charged particles called electrons.
J. J. Thomson
Thomson discovered that the
atom was not a solid sphere.
He used a cathode ray tube to show
the that atoms were (at least
partially) composed of negatively
charged particles called electrons.
J. J. Thomson
Thomson discovered that the
atom was not a solid sphere.
From this data, he postulated the
“raisin pudding” model of the
atom in 1897.
J. J. Thomson
Thomson discovered that the
atom was not a solid sphere.
The atom is a sphere of positive
charge ...
J. J. Thomson
Thomson discovered that the
atom was not a solid sphere.
The atom is a sphere of positive
charge ...
J. J. Thomson
Thomson discovered that the
atom was not a solid sphere.
The atom is a sphere of positive
charge with negatively charged
electrons imbedded in the
sphere.
J. J. Thomson
Thomson discovered that the
atom was not a solid sphere.
The atom is a sphere of positive
charge with negatively charged
electrons imbedded in the
sphere.
Robert Millikan
Robert Millikan
Millikan determined the charge
of the electron.
Robert Millikan
He used his “oil drop”
experiment.
Robert Millikan
He used his “oil drop”
experiment.
Robert Millikan
He used his “oil drop”
experiment.
Oil was sprayed into a chamber
and allowed to fall into a
charging chamber.
Robert Millikan
He used his “oil drop”
experiment.
The oil drops were charged
(ionized) between two charged
plates with x-rays.
Robert Millikan
He used his “oil drop”
experiment.
The speed of the oil drops were
dependent on the charge of the
drops.
Robert Millikan
He used his “oil drop”
experiment.
After thousands of experiments,
Millikan determined the charge of
the electron.
Robert Millikan
He became one of the first
American scientists to win a
Nobel Prize in Physics for his
work
Hantaro Nagaoka
Hantaro Nagaoka
In 1904, he published a paper
where he envisioned the
“Saturnian Model” of the atom.
Hantaro Nagaoka
In 1904, he published a paper
where he envisioned the
“Saturnian Model” of the atom.
In this model, the electrons of the
atom circled a massive nucleus.
Hantaro Nagaoka
In 1904, he published a paper
where he envisioned the
“Saturnian Model” of the atom.
In this model, the electrons of the
atom circled a massive nucleus.
The electrons would be held in
place by electrostatic attraction.
Hantaro Nagaoka
In 1904, he published a paper
where he envisioned the
“Saturnian Model” of the atom.
In this model, the electrons of the
atom circled a massive nucleus.
The electrons would be held in
place by electrostatic attraction.
He eventually abandoned the
model in 1908.
Ernest Rutherford
Ernest Rutherford
Rutherford used alpha particles
(positively charged particles) to
explore the structure of the atom.
Ernest Rutherford
He shot these at gold foil and
looked at the deflection of the
particles.
Ernest Rutherford
He shot these at gold foil and
looked at the deflection of the
particles.
Ernest Rutherford
He was surprised to see that some
of the particles bounced back at
him.
Ernest Rutherford
He was surprised to see that some
of the particles bounced back at
him.
?
Ernest Rutherford
From this data he proposed the
“solar system” model of the atom.
Ernest Rutherford
From this data he proposed the
“solar system” model of the atom.
Ernest Rutherford
From this data he proposed the
“solar system” model of the atom.
This is the most common view of
the atom.
Summary
There were some in antiquity who
postulated the existence of atoms.
Summary
There were some in antiquity who
postulated the existence of atoms.
But, they couldn’t provide any
demonstration of the validity of their claim.
Summary
John Dalton used experimental results as
the basis for his theory of atoms.
Summary
John Dalton used experimental results as
the basis for his theory of atoms.
This was a theory of behavior, not of
structure.
Summary
John Dalton used experimental results as
the basis for his theory of atoms.
This was a theory of behavior, not of
structure.
Dalton knew how atoms would react but
not what in the structure allowed that
reaction.
Summary
Thomson discovered the electron.
Summary
Thomson discovered the electron.
Rutherford discovered the nucleus.
Summary
Thomson discovered the electron.
Rutherford discovered the nucleus.
This led to the “solar system” model of the
atom.
Summary