Transcript Atomic Modelx

The Atomic Theory
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Atomic Theory Matching
Atom Size
Democritus
Dalton – Ball Model
J.J. Thompson – Raisin Bun Model
Rutherford – Gold Foil Experiment
Bohr – Energy Level Model
Whose theory was it anyways?
- Match the scientist with his model
of the atom as well as his atomic
explanation.
How are atoms studied?
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Atoms are the building blocks of matter
Atoms are too small in size to study easily
Size of Earth : soda can = soda can : atom
Online Simulation
Sizing up the Atom
Materials are able to be subdivided
into smaller and smaller particles – these
are atoms.
 If you could line up 100,000,000
copper atoms in a single file, they
would be approximately 1 cm long
The Size of the Atom
Despite their small size, individual atoms
are observable with instruments such as
scanning electron microscopes
In this picture, atoms are being
moved by the single atom tip of
a Atomic Force Microscope
(AFM). Apart from allowing
scientist to image atoms, this
instrument also allows them to
actually move them one at the
time.
The Atom is Really, Really Small!
Just How Small Is An Atom?
The Greek philosopher Democritus (460
B.C. – 370 B.C.) was among the first to
suggest the existence of atoms
 He believed that atoms were indivisible
and indestructible
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Dalton’s Atomic Theory – The
Ball Model: 1800s
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Referred to the atom as a small, hard,
indestructible sphere that cannot be subdivided
Different atoms have different properties
An atom is the smallest particle of an element
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an element is a substance made up of only 1 type of
atom
J.J. Thomson
In 1897 J.J. Thomson demonstrated that
there are negatively charged particles found
within atoms using cathode ray tubes
 After further investigation he concluded that
the same negatively charged particles are
found in all atoms
 These are now called electrons (e-)
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Thomson’s Model
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He knew atoms didn’t have
a charge (+ or -)
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Since his particles were
negative, he knew that there
must also be positively
charged particles within the
atom
J. J. Thomson
Thomson’s Atomic Model
• Thomson believed that the electrons were
like plums embedded in a positively charged
“pudding”
• It was called the “Plum Pudding” or
“Raisin Bun” model.
Ernest Rutherford’s
Gold Foil Experiment - 1911
 “+” charged particles (alpha particles) were
fired at a thin sheet of gold foil
 Particles that hit on the detecting screen
(blue film) were recorded
What he thought would happen
given the “Plum Pudding” Model
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Some alpha particles would be slightly diverted due
to their avoidance of the other positive particles
inside the atom
What he actually found
Most of the alpha particles slightly deflected and
carried on but some bounced backwards
 Therefore, they must have collided and
rebounded off something very dense
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Rutherford’s Gold Foil
Experiment
Rutherford’s Findings
Most of the particles passed right through
 A few particles were deflected
 VERY FEW were greatly deflected (1 out
of 8000!)
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Egads! It’s like shooting bullets at tissue
paper and watching them bounce back
The Rutherford Atomic Model
Based on his experimental
evidence he concluded that the
atom:
 Is mostly empty space
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Contains a small, dense,
positively charged nucleus at
the center
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Negatively charged
electrons revolved around
the positive nucleus
Bohr - 1912
Niels Bohr
If there are negatively charged
particles around a positively charged
nucleus, why don’t they attract and
collide (opposites attract)
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The Bohr-Rutherford Model
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Central positive nucleus
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Electrons move in orbits
(energy levels) around the
nucleus
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Electrons more or less stay in
their orbit unless an increase
in energy causes them to
move
Atom Animation