Key
Components
Dalton
1808
-All matter is composed
of atoms
-Atoms are indivisible
and indestructible
-All atoms of the same
element are identical in
mass and properties
-Compounds are formed
by a combination of two
or more different kinds
of atoms
-A chemical reaction is
a rearrangement of
atoms
Dalton
-Atoms are divisible because
there are protons, neutrons,
and electrons
-All atoms of the same element
are not identical in mass
because of isotopes
Limitations of
Atomic Model
Diagram of
Atomic Model
Gave credibility to
Democritus’s idea
Conclusions /
Contribution
to Atomic
Theory
-First evidence-based
explanation of the atom
-Gave a definition of a
compound and of
chemical reactions
Other Images
Associated
with Model
Key
Components
Quantum
1940’s- now
-Mathematical model
-describes region of space
(cloud) where an electron will
probably be
-Electron clouds are called
orbitals: s, p, d, f
-Only 2 electrons can be in an
orbital at the same time and
they must pair with opposite
spin
-Sometimes called the
Quantum Mechanical Model
Other Images
Associated
with Model
Conclusions /
Contribution
to Atomic
Theory
Quantum
-Theoretical physicists
are developing theories
for exceptions to the
quantum model
Limitations
of Atomic
Model
Diagram of
Atomic
Model
-Current Atomic Model
Gives an atomic model based
on probability and geometric
shapes
-Electrons have certain allowed
quantum “numbers”
(characteristics)
-Treats electron as both a wave
and a particle
Other
Images
Associated
with Model
1s, 2s, and 2p images
around a nucleus
Thomson
Key
Components
1897
Plum Pudding Model
-Discovered
electron using an
Limitations of
experiment
Atomic Model
involving cathode
ray tube
Thomson
-No explanation why the protons
and electrons do not attract and
bond to each other
- No proof of the proton just a
theory at this time.
-No organization to the sea of
positive charges (protons) and
negative charges (electrons)
Diagram of
Atomic Model
-Unlike Dalton
proved an atom is
divisible due to
the discovery of
Conclusions / the electron.
Other Images
-Negative electrons
Contribution
Associated
to Atomic
are surrounded by a with Model
Theory
soup of positive
charges
-Gives subatomic
particles to the
atom
Thomson’s Cathode Ray Tube
Key
Components
Rutherford
1911
Gold Foil Experiment:
-Fired a beam of alpha
particles directly at a
thin sheet of gold foil
-The particles were
predicted to pass
straight through, but a
small fraction of them
bounced back because
they had collided with
something within the
atom
Limitations of
Atomic Model
Rutherford
-No explanation for location of
negative electrons other than
outside the nucleus.
-No explanation for why the
electrons and protons are not
attracting to each other.
Diagram of
Atomic Model
Conclusions
/
Contribution
to Atomic
Theory
-Proves nucleus at the
center of the atom
where protons are
tightly packed together
-Nucleus is dense (high
mass in small volume)
and positively charged
-Rest of the atom is
mostly empty space.
-Came after
Thomson’s Plum
Pudding Model
Other Images
Associated
with Model
Top: Gold Foil Experiment Predicted
Bottom: Gold Foil Experiment Results
Key
Components
Bohr
1913
-The atoms has a small,
positively charged
nucleus surrounded by
electrons that travel in
circular orbits, similar to
the planets in the solar
system
Bohr
-Simplistic in its treatment of
the electron path as a simple
circle, instead of a 3D shape
Limitations of
Atomic Model
Diagram of
Atomic Model
-Gave an idea of
where electrons are
located after
Rutherford
-Gives quantized energy
Conclusions / levels for the orbit of
Contribution
electrons, which explains
to Atomic
why the electrons do not
Theory
fall into the nucleus
-Explains the behavior or
electron energy level
transitions for a
hydrogen atom model
Other Images
Associated with
Model
The emission spectrum of
hydrogen showing quantized
energy transitions for electrons
Democritus/Aristotle
400BC
Democritus:
Matter is composed of
“atomos”
Key
Components
Aristotle:
Basic building block of
matter is composed of
4 elements: earth,
wind, water, and fire.
Limitations
of Atomic
Model
Democritus
vision of the
atom
First Idea of the
Atom
Most people believed
Aristotle’s vision of
matter.
Conclusions /
Contribution
to Atomic
Theory
Aristotle’s
belief of
what matter
is made of.
Democritus/Aristotle
-Neither Democritus nor Aristotle
did any research or experiments
to try and determine what matter
is composed of.
Both were philosophers.