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Transcript
The Atomic Model
Define: Atom
 An
atom is the smallest
component of an element that
retains the characteristics of the
element
What atoms are made of ?
 If
you broke apart any one atom, it
would be made of three parts- and it
wouldn’t be the atom anymore.
 Atoms
are made from three different
sub-atomic particles:
• Proton
• Neutron
s
• Electron
A brief history of Atoms







460 B.C. Democritus: pounded stuff into itty-bitty pieces
1808 Dalton: small solid spheres
1898 Thompson: atoms eject tiny negative particles!!!!
1904 Thompson: Plum pudding model
1910 Rutherford: Gold foil expt
1913 Bohr: Electrons in ORBITS!
Modern Theory (Wave Theory): electrons are wavelike,
NOT arranged in neat orbits, but can be discussed only by
the probability of where they are. (Electron Cloud)
Democritus (460 – 370 BC)
 Eventually
reach matter
that cannot be divided:
which he called an
“atom”.
John Dalton (17661844)
 Elements
combine in
certain ratios
1803: Dalton proposes
“Atomic Theory”
 All
Matter is composed of tiny,
indivisible particles called atoms.
 Atoms
of a given element possess
unique characteristics and mass
 Atoms
of different elements can join to
form compounds.
Joseph John
Thomson
(1897)
 Discovered
 Proposed
electrons
“Plum Pudding” model
Rutherford
 Discovered
the nucleus
 According to his
model, an atom is
mostly empty space.
Stadium Analogy
 If
a football is placed on the 50 yard line (in
the middle) of a football field then the outer
seats are the edge of the electron cloud
and the football is the nucleus. Everything
in the stadium (atom) other than the
football is empty space.
Niels Bohr
 Proposed
that each
electron is in a specific
energy level.
 Bohr’s model is also
called the “planetary
model”
Bohr Model
Write the number of protons
and neutrons in the center
 Up to 2 electrons on the inner
ring, and up to eight on the
second ring. The third ring can
have up to 16 electrons.

P=
N=
Cloud Model
 Erwin
Schrödinger
 The cloud model represents a sort of
history of where the electron has
probably been and where it is likely to
be going.
 It utilizes Heisenberg’s uncertainty
Principle
The structure of an atom
Bohr Model
Schrödinger Model
“Planetary Model”
“Electron Cloud Model”
Lewis Dot Model
Dots are drawn
for each OUTER
electron
 Not all electrons
are drawn

Valence Electrons
 Electrons
located on the
outermost energy level.
 Use the columns on
periodic table!!!
Dmitri Mendeleev
Russian scientist/professor
Citations
History of the Atom Timeline: http://cstlcsm.semo.edu/mcgowan/ch181/atomhist.htm