Download atomic theory of matter

Atomic Theory
What is it?
 Who figured it out?
 When did they do it?
 How did they do it?
 Why do we believe it?

What can you tell from this picture?
What is an ATOM?

An atom is the smallest particle of an
element that retains the identity of the
element.
ZZZ
ZZZ
ZZZ
ATOM
Atoms combine to form compounds
The Ancient Greeks

Democritus
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Lived 450 B.C.
Proposed that all the
stuff in the world is
“atomos”
Tiny, indivisible
particles

Aristotle
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Questioned theory of
Democritus
Rejected it for lack of
proof
Roger Bacon
Lived in 13th century
 Believed that science should be based on
experimental evidence.

ALCHEMISTS

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Tried to turn base
metals into precious
metals.
Developed
knowledge and
techniques
Not true scientists
Copper into Gold Laboratory

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Alchemists tried to
turn normal copper
into gold coins!
If they succeeded,
they would never
need to work!
Prove that the coins are GOLD
How is copper different than gold?
 How can you test it?
 What techniques are you using…that
Democritus did not use?

Antoine Lavoisier
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1743-1794
French
Father of Chemistry
Sadly, beheaded in
French Revolution
Lavoisier

LAW OF CONSERVATION OF MATTER

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Matter, like energy, is neither created nor
destroyed in a chemical reaction.
This concept established modern chemistry.
What was different?

Experimentation

He used a balance to
study the role of
oxygen in rusting and
burning.
Other people did it, too!


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Priestly did similar
experiments.
He believed a false
theory of Phlogiston.
Kept his mind closed
to new idea.
PROUST


WATER
11%
Hydrogen
WATER
89%
Oxygen
1799
Law of Constant
Composition

A given compound
always contains the
same elements in the
same proportion by
mass.
JOHN DALTON
LAVOISIER
PROUST
ATOMIC THEORY OF MATTER
DEMOCRITUS
BACON
DALTON’S ATOMIC THEORY OF
MATTER
1.
All matter is composed of
submicroscopic (extremely small) indivisible
particles called ATOMS.
2.
All atoms of a given element are
identical. The atoms of any one element are
different from those of any other element.
DALTON’S ATOMIC THEORY OF
MATTER
3. Atoms are neither created nor destroyed in a
chemical reaction. Chemical reactions occur
when atoms are separated, joined, or
rearranged. However, atoms of one element
are never changed into atoms of another
element as a result of a chemical reaction.
DALTON’S ATOMIC THEORY OF
MATTER
4. Atoms of different elements can mix
physically or can combine chemically with one
another in simple whole number ratios to form
compounds.
What does this mean?
Not perfect...
but a workable theory to build on.
Atomic Theory of Matter
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Scientists had been doing many
experiments with electricity since
Ben Franklin flew his kite.
Faraday suggested that electricity
might explain the atom
English physicist, J.J. Thomson
1856-1940
Discovered electrons in 1897
Thomson experimented with a
“cathode ray tube”
Cathode Ray Tube
Cathode Ray Tube
Thomson’s Cathode Ray Tube
Experiment

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Flow of electric current through gases.
Sealed gas in glass tube with metal plates at the end.
Connected plates to high voltage source:
Anode + and Cathode –
This ray could be deflected
toward a positive
charge…
It has a negative charge.
This ray could move
things…
It was made of particles of
matter.
This ray acted the same no
matter what materials
were used…
It was not atoms…it must be
part of all atoms
Cathode Ray Tube
Cathode ray is composed of very small
negatively charged particles that are part of
atoms
ELECTRONS
Cathode Ray Tube
Diagram of CRT
Atomic Theory
Millikan devised experiments to determine
the mass and charge of the electron.
 Protons : discovered in 1886
Positively charged particles
Also discovered with cathode ray
tube…these particles went the other
direction.

The Nuclear Atom

Rutherford
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Identified three types of radiation
 Alpha…positive
particle
 Beta…negative particle
 Gamma…high energy

Devised the GOLD FOIL EXPERIMENT
Now…where were we….?
Rutherford’s Nuclear Atom

Most of the mass of
an atom is in the
center…the
nucleus…with
electrons moving
around it.
Nuclear atom
By 1932, neutron was discovered, too.
 The nucleus is the central core of the
atom, composed of protons and neutrons.
Because, protons and neutrons have
much greater mass than electrons, almost
all of the mass of the atom is concentrated
in a tiny nucleus…a dime in a football
stadium!

What next?
We know the parts of the atom.
 We know about the nucleus.
 What about the electrons?

Bohr’s Model
 Light
provided
the next clues for
the structure of
the atom
Light has a Dual Nature
Like this
picture…
Young lady
or
Old lady?
Light is a wave
Electromagnetic radiation travels in waves.

As the wavelength increases, the frequency
decreases.

The greater the frequency the greater the
energy.
Light acts like Particles

Electromagnetic radiation also has the
properties of particles.

Bohr suggested that energy is emitted and
absorbed in discrete quantities called
Quanta or Quantum
packets or pieces of energy
“Jumps”
Demonstrate Quantum
Dual Nature of Light is the next tool
for understanding the atom
Energy is directly proportional to
frequency…wave nature.
 Einstein proposed that light consists of
quanta of energy that behave like particles
of light…he called these photons.
 Example: photoelectric effect
This is the DUAL NATURE OF LIGHT

Continuous Spectrum vs.
Line Spectrum
What does this have to do with
ATOMS?
Atoms give off energy as photons of light.
 Line spectra of elements reveal that
electrons exist in quantized (discrete)
energy levels.

Rainbow…continuous spectrum
 Line…discontinuous spectrum

 The
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color allows us to calculate the energy
higher frequency = higher energy…
purple higher than red
Emission Spectra
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Line Spectra of elements
show discrete or quantized
energy levels in the atom.
These energy levels are
different for each element.
The color or wavelength of
light shows the energy level
because energy can be
calculated from frequency of
light emitted.
Bohr’s Model of the Atom
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Bohr applied Quantum
Theory to the structure of
the hydrogen atom.
Quantum theory means
that electrons jump from
level to level.
Bohr pictured the
electrons spinning around
set orbits, like planets
around the sun.
Planetary Model
Quantum Leaps!
Electrons exist at low energy…
ground state
 Add energy to go to higher energy…
excited state
• Electron drops back down to ground
state as soon as it can
• It releases the exact energy it needed to
jump up as a photon of a frequency or
color.

Schroedinger’s
Quantum Mechanical
(Today’s) Model
We still have energy levels, like Bohr
 Heisenberg Uncertainty Principle

It is impossible to know the velocity and
position of a particle at the same time
 We can not know the exact location of an
electron.
 Any effort to do so, will change the position.
 We can only figure the probability of finding it
in a certain region.

Orbitals
Area where electrons are most likely to be
found.
 Example:
If your mom wants you to do some work,
she can find you in your room most of the
time, or the house, or the yard…but you
could be at the mall.
And sometimes her efforts to find you,
make you move!

Today’s Atom
Dense,
small,nucleus (with
protons and
neutrons) is
surrounded by a
fuzzy cloud shapes
where electrons
(that act more like
waves) are most
likely to be found…
orbitals.
Today’s Model of the Atom
aka
Schroedinger’s
or
Quantum
Mechanical
Model
Links
Go to Holt On-Line for a nice review of all
this.
my.hrw.com/
 Go to this site to see some great atomic
atrwork!

www.chemsoc.org/.../orbital/images/elev3.jpg
The Crazy World of Quantum Mechanics
“If you aren’t shocked by it, you don’t
understand it.” Bohr