The Atom

1
The Atom
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ATOMIC HISTORY

• The main goal is to develop a mental picture and
  understanding of the basic structure of the atom.
• You will learn about many of the main
  contributors whose insight and determination led
  to atomic discoveries.
• You will gain an understanding about the time
  line of discovery and sense the importance of
  knowing what the atom is like.

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Ok, so what is inside this atom thing?
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The Story Begins with the Ancient Greeks.

• Sounds like Greek to me.
• (Actually the story does begin with the ancient
  Greeks)

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Did you ever wonder what things are made of?
(Well you should have.)

• Pick up a tiny grain of sand. Is there anything
  smaller?
• Look closer at a drop of water. How many times
  can you cut it in half and still have water?
• Why can we feel the wind, but not see it?

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These were the type of questions that the ancient
Greek philosophers would ask. Finding order and
harmony in nature and life were important ideas
that needed to be thought about and debated.
Enter Leucippus Democritus
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Democritus and his atom.

• To the best of our knowledge a man by the name of
  Leucippus in the 5th century BC came to the
  conclusion that matter was made of smaller pieces
  that he called a-tomos, the origin of
  our word atom.
• Democritus (460-370BC),a student of Leucippus, is
  credited for expanding this concept further.

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Democritus and his atom

• All matter is made up of individual particles
  called atoms.
• There is a void, emptiness, between atoms. Atoms
  are held together by an undiscovered force.
  (static electricity)
• Atoms are solid and unbreakable.
• Atoms are homogeneous, the same, with no internal
  structure.
• Atoms vary in size, shape, weight, and color.
  There is some debate as to how much he believed
  in this last point. Taught this late in life.

9
Along comes Empedocles

• Atoms may or may not exist. But if they do, then
  there are four types. Each type makes or comes
  from a basic element.
• Earth Atoms/element
• Air Atoms/element
• Fire Atoms/element
• Water Atoms/element

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The Four Elements of Nature
Matter is made of four elements. Each type of
matter has a fixed amount of each element.
However, the ratios of these elements to each
other change as the various types of matter
interact with each other. Thus creating qualities
of matter
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Aristotle says...
"It ain't so."
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Aristotle (384-322 BC)

• He became the tutor of Alexander the Great.
• He was very interested in the natural world and
  wrote extensively about nature.
• He regarded the world as being made up of
  substances occurring in fixed natural kinds. With
  each drawing substance from others. THERE IS NO
  VOID, THERFORE NO ATOMS!
• Each individual has its built in specific pattern
  of development. Therefore, growth, purpose, and
  direction are thus built into nature.
• He was a student of Plato and eventually became a
  teacher at Platos school for over 20 years.

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Aristotle NO ATOMS

• Aristotle believed that the elements, being part
  of nature and in a sense nature itself, formed a
  continuum of mass and therefore no void (vacuum)
  could exist. Thus, atoms could not exist.
• He taught that there were four elements of nature
  and they were composed of four qualitiesheat,
  cold, moisture, and dryness.
• For example, fire was made of heat and dryness,
  water was made from cold and moist.
• Elements are made from the qualities, and
  qualities change.

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KEY POINT !

• Aristotle taught that since it was possible for
  the amounts of each quality to change in an
  element, the elements could be changed into one
  another thus it was also thought possible to
  change the material substances that were built up
  from the elements.( given the right
  circumstances)
• In essence matter could change form !

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Did you ever play the game

• Susie says that Tommy has three yucky frogs in
  his pocket and he is going to give two of them to
  Bobby and one to Billy. Then they are going to
  throw them at Mary when she is walking to the
  mall with Matt and Fred.
• (pass it on)
• Aristotles theory was accepted by the artisans
  and philosophers of his day. Especially in
  Alexandria, Egypt which had become the
  intellectual center of that era.
• In time, Aristotles ideas slowly were changed
  into the opinion that metals in the earth seek to
  become more and more perfect and thus would
  gradually change into gold.

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How could this happen ????

• Greek empire is absorbed into the Roman Empire.
  The Romans were great copy cats. They kept what
  they liked and destroyed what they did not like.
• In time, the Roman empire falls and is replaced
  by the barbarians.
• Barbarian cultures are not overly interested in
  higher education. Therefore many ideas are
  forgotten about.
• Sometimes ideas and opinions are mixed in with
  observations and the results are, more weird,
  than correct.
• The slinky is alive ! (But its movingright?)

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What did all of that mean?

• The beliefs of people slowly change with time.
• Many factors influence these changes.
• In this case, in the minds of man, cheap common
  metals can be changed into gold because elements
  naturally want to change.

Really a blessing in disguise. It inspires a
search. Alchemy begins !
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OK, So what is the magic formula needed to make
this change happen ?
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The Philosophers Stone
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The search for the Philosophers Stone will drive
men for centuries. It will lead to the growth of
Kings and Kingdoms. Be the root cause of some
wars and inspire the continual search for new
knowledge. And ultimately lead to the discovery
of the atom.
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Part Two

• The exchange of ideas.

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Alchemy to Dalton in less than two slides. (maybe)

• During the 13th and 14th centuries the influence
  of Aristotle on all branches of scientific
  thought began to weaken.
• Why ? ? ?
• Accurate observation of the behavior of matter
  and the workings of nature were emphasized.
• The invention of the printing press allowed
  knowledge to spread.
• The philosophers stone was never found.

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The beginning of true science.

• The alchemists failed in the attempt to find the
  elixir of life and in turning lead into gold.
• They discovered processes that were far more
  important because they experimented.
• In the 16th century they found something that
  Aristotle believed could not be true. They found
  out how to make a vacuum. (Not a vacuum
  cleaner silly)
• This revived the almost forgotten ideas of
  Democritus. That matter, atoms, move through a
  void and have specific properties.

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Discoveries in chemistry change the nature of
the world.

• 1700s Contributions by Newton, Becher, Stahl,
  Lavoisier, Hales, Black, Cavendish, Priestly,
  Berzelius, Gay-Lussac, and many, many others make
  significant contributions to the understanding of
  the nature of matter.
• The behavior of matter follows certain rules.
• John Dalton, a school teacher, and an amateur
  scientist, has a mental break through with
  respect to the rules which control how matter
  behaves. The year is 1803.

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Of John Dalton
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Daltons Atomic Theory

• All matter consists of tiny particles, atoms, of
  different sizes.
• Atoms are indestructible and unchangeable.
• Elements are characterized by the mass of their
  atoms. Atoms of the same kind are identical to
  each other.
• When elements react, their atoms combine in
  simple whole number ratios.There is much more
  to this one.
• Only unlike atoms can combine. This is due to
  the fact that static charges either attract on
  repel. Dalton assumes this transfers to the
  atom.

If you understand the atom, you will understand
the rules
Billiard Ball Atom
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Is it H O or H2O ? (Only his hair dresser knows
for sure)

• Dalton is correct about the basic nature of the
  atom.
• He is wrong about the idea of only unlike atoms
  combining.
• Science has discovered electric charge and has
  learned the rules of attraction and repulsion.
• It was only logical to transfer this information
  to the new atomic theory.
• Atoms of the same charge should repel each other.
  Different atoms should attract each other and
  form new compounds.
• Dalton says that the formula for water can only
  be H O not H 2 O because it is made of
  oppositely charged atoms.
• Gay-Lussac thinks that this is wrong, based upon
  his volume of gas experiment. Two parts of
  hydrogen for every one part oxygen obtained.
• This debate is somewhat based upon political
  lines. Never the less, this debate plugs up
  much scientific development for almost the next
  50 years.

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The Search Begins

• Daltons theory had mistakes that were quickly
  found. However it was basically correct. What
  it did was throw fuel onto the fire. That fire
  being the search for knowledge.

For the first time, a logical explanation of how
elements combine to make new substances is
offered
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Its about timeIts about space Its about your
funny face.

• The scientific revolution of the late 1700s and
  1800s is crumbling old ideas quickly.
• Joseph Gay-Lussac in the early 1800s
  experimentally suggests that when gases combine
  they do so in whole number ratios by volume. Ex.
  Water breaks down into twice as much Hydrogen as
  there is Oxygen. Suggests that the formula of
  water is H2O.
• This disagrees with Daltons work.

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EnterLorenzo Romano Amedeo Carlo Avogadro di
Quareqa e di Carreto

• Dalton argues that Gay-Lussacs work is wrong.
  There is mixed reaction to this claim. One
  person in particular, Mr. AA states that Dalton
  is wrong.
• AA is rejected and will die in obscurity.
• A friend of As Stanislao Cannizaro makes a
  presentation at the first international
  conference of Chemistry in Karlsruhe, Germany in
  1860.
• This conference was trying to solve the
  difference between Atoms and Molecules.
• Dalton and others thought that only different
  atoms could combine to make molecules. Ex. H O
  could exist, but never H H O.
• But, way back in 1811, AA proved Dalton wrong.
• Acceptance of AA at the conference inspires
  Dmitri to put on weight.

I think the formula is H2O not H O
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The first Periodic Table of the elements.

• Dmitri Mendeleyev , in 1871, systematically exams
  the masses of the known elements and creates the
  periodic table. Predicts the existence of many
  undiscovered elements. His predictions are based
  upon the mass (size)of the atoms. He now
  believes that the basic nature of the atom allows
  it to exist combined with atoms of the same kind
  and combined with other atoms, that are
  different.
• Thanks to AA for his ideas.

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We are not in the stone age any longer, Toto.

• It is imperative that you understand that
  throughout the mid to late 1800s technology is
  developing at a rapid pace.
• Thomas Edison is inventing great new machines.
• The internal combustion engine has been
  invented. Automobiles soon follow.
• Society is moving along clamoring for more
  things.
• People living then were not just stupid stone
  chippers.

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X-Rays Discovered

• November 8th,1895 Wilhelm Roentgen noticed that
  cathode rays, under certain conditions,would
  seemingly pass through objects of various
  densities causing shadows to form on photographic
  plates. Called these mysterious rays X-rays.

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MAJOR DISCOVERY

• Antoine Becquerel discovers radioactivity in
  March of 1896 (by accident)

Mysterious rays being released from mineral
samples.
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Part Three You mean that there really are
atoms?

• Or, in other words, look what we found.

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What have we found ?
What was once thought to be a hard, round,
indestructible particle has now raised new
questions. What are these mysterious rays coming
from these rocks? What is their source? Why do
they exist? What are these X-Rays that can go
through your body? Here our story takes splits
into two distinct paths. One of which traces the
story of radioactivity, the other takes us inside
the atom. This is the one we will follow.
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Enter J.J.Thomson and his corpuscles.

• In 1897, J.J. Thomson, working at Cambridge
  University in England, was studying the
  mysterious cathode rays. Taking inspiration
  from Becqurel , Roentgen and the Curies, Thomson
  suggests that the rays are streams of tiny
  particles he calls corpuscles.
• The discovery of radioactivity was world
  changing. No one had thought that it might be
  possible for atoms to be made of smaller
  particles. Something, however, had to be the
  source of this remarkably powerful energy.

Since rays cannot be charged, the X-Rays and
this radioactivity must be a type of particle
coming from inside the atom.
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Corpuscles become electrons.

• Thomson was not without critics. There were
  plenty. But he was a clever experimenter. He
  challenged other scientists to duplicate his work
  and report on their findings. One such person
  was Heinrich Hertz of Germany. He placed a
  strong magnet next to one end of the cathode ray
  tube and the particles bent toward the positive
  end of the magnet.This proved what Thomson
  discovered earlier that these particles were
  charged. Other scientists discovered that these
  particles could pass through thin metal foils
  placed in their path. A German name Emil Wiechert
  made a measurement indicating that the electrical
  charge on these particles was over 1000 times
  smaller than the electrical charge of an entire
  atom.

PROVE ME WRONG
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1897 Thomson declares that the atom is made of
two substances.

• JJ advances the idea that cathode rays are
  really streams of very small pieces of the atom
  which carry a powerful negative electrical
  charge.
• He is really the second person to think this,
  but his experiments prove this theory before
  anyone else.
• We have in the cathode rays matter in a new
  state, a state in which the subdivision of matter
  is carried much further than ordinarythis matter
  being the substance from which all the chemical
  elements are built up.
• If there is a negative then there exists its
  opposite a positive.

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Yummy for the tummy ! Plum Pudding
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Do you like plum pudding?

• The word electron was coined by G. Johnstone
  Stoney in 1891. Some of Thomsons critics
  started calling his corpuscles electrons, and the
  name was eventually adopted by Thomson himself.
  Eventually Thomson revised his theory to resemble
  a plum pudding. Imagine thousands of electrons
  (negative charge) swimming around inside a
  substance that carried a yet undiscovered
  positive electrical charge. Now the atom had an
  electrical nature. It had two distinct parts,
  the negative electron and the positive mass.
  Also, somehow, somewhere, there lurked a source
  of very powerful energy inside the atom. But
  where could it be ?

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TINY, BUT MIGHTY
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Sorry J.J. old boy. Youre wrong.

• In 1895 J.J. invites a brilliant young scientist,
  an Australian, to come to the Cavendish
  Laboratory at Cambridge University and study
  under him. This man was named Earnest
  Rutherford. He and J.J. begin to study
  Roentgen's X-Rays.
• Rutherford had tremendous powers of concentration
  and made a series of remarkable discoveries about
  how certain types of matter react to electrical
  charges.

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1911 Thomsons plum pudding gets eaten. (Thanks
Ernieburp)
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Rutherford Discovers the Nucleus

• In 1911 he made one of his greatest contributions
  to science. Based on knowledge gained from
  previous experiments he believed that there was
  more to this positive mass than was being
  considered. He had been using Alpha Particles
  (really the nuclei of helium atoms) to measure
  high energy movement through matter.
  Calculations indicated that to get Alpha
  particles to deflect off their path, about
  100,000,000 electron volts of electricity would
  be required. Working with two of his students,
  Charles Geiger and Ernest Marsden, Rutherford
  proposed this question, could Alpha particles be
  deflected off course by heavy atoms such a gold ?
  
• The result of the famous gold foil experiment
  shocked not only Rutherford, but the rest of the
  world.

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Alpha Particle Scattering Device
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It was as if I had shot a cannonball at tissue
paper and it bounced off.

• Rutherford's team discovers that if all of the
  positive mass is condensed in a central location
  within the atom, then the electrical voltage
  required to deflect Alpha Particles dramatically
  off course would be there. This is exactly what
  happened. Therefore, the conclusion was the atom
  has a dense, electrically positive center called
  the nucleus. This area has an electrical charge
  that balances the electrical charge from the
  electrons.

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A nucleus with electrons around it in no precise
order.
Rutherfords atom was never given a nickname
except for being called Rutherfords Atom.
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Are we there yet?
Are we there yet ?

• No, not yet. However we are ready to go to part
  4. So hang on tight, I am going to hit the gas.

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I hope this is not too Bohr ing.

• In 1913, two years later, a Danish scientist,
  Niels Bohr, thought that electrons were not
  randomly around the nucleus. He thought that If
  they did move they would eventually crash into
  the nucleus. Instead he believed they moved in
  orbits around the nucleus. He organized them
  into energy levels he named K L M N O P Q.
• What was his inspiration? Just put a pin into a
  flame. Why does it glow red? In other words,
  what is creating the light?

• Rutherfords experiment proved that the atom had
  a dense center region that he called the nucleus.
  It is where the dense positive mass resided.
  Surrounding it were electrons, randomly placed.
• But how many electrons, exactly? Where were
  they? Evidence suggested that they move, but how
  do they move?

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• It sounds stupid really. Watching a pin get red
  hot and cool off over and over again. However,
  they say inspiration comes when you least expect
  it.
• Bohr figured out that electrons orbit, or move
  around,the nucleus at fixed energy levels named
  K l M N O P Q . Electrons are a precise
  distance from the nucleus. If the electron
  absorbs energy it will jump to a higher orbit.
  If the electron loses energy it will return to
  its original position, its ground state. The
  energy released is a photon of light. This causes
  the pin to glow. When the electron returns to its
  original position the pin will dim.

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The Solar System Atom of Bohr

• For the most part Bohr has correctly discovered
  the real structure of the atom. There were some
  inaccuracies, but even today we still use his
  model because of its correctness and simplicity.

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Is there more ? You betcha' there is. Here
comes the Prince.

• In 1923, Prince Louis de Broglie argued that
  since light was considered to have properties of
  both particles and waves then perhaps the
  electron had this dual nature as well. He will
  prove this with mathematics. The mental picture
  needed to understand this is to visualize a
  guitar string anchored at each end. Once it is
  fastened down, its vibration pattern, the musical
  note it will produce, can be predicted.

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De Broglie sees the nucleus surrounded by
electrons(as particles) moving in confined energy
levels in wavelike motion.

• Sounds can be made by plucking the string. The
  tone can be changed by either shortening the
  string or making it longer. The range of notes is
  limited and well known. de Broglie suggested
  that when an electron is confined in orbit around
  an atom, its wave like behavior can be predicted
  also.

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The modern modelThe Electron Cloud

• Based upon math models only, de Broglie and
  others suggest that the electron oscillates in a
  confined space, which is its orbital or energy
  level. It must do so evenly distributed
  throughout this orbital. If it didnt, the atom
  would destroy itself.
• Since each orbital is a different size, because
  it contains different numbers of electrons, these
  standing waves cause the shape of the orbital to
  change. The result is a complex arrangement of
  electrons around the nucleus.
• These arrangement of electrons creates the
  ELECTRON CLOUD.

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A cloud of electronsand more

• What now happens is really very simple, but it
  requires a detailed understanding of advanced
  math. You are not ready yet for these
  explanations. Many other top notch scientists
  expand de Broglies theory until it is what it
  has become today.
• The electron behavior is mostly understood, but
  its motion is unpredictable. Hence it can be
  anywhere on its energy level at any given time.

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Into the 1920s , 1930s and 1940s

• Scientists are certain that the electron now has
  a dual nature. It exists in orbitals around the
  nucleus These paths, or energy levels, that the
  electrons travel in are constantly changing
  shape. Experimenters and mathematicians soon
  suggest that the electrons orbit in a wave like
  motion. Electrons are capable of absorbing and
  releasing energy and can jump around within
  their main energy level something like cars
  changing lanes on a super highway.

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The story is not over, but were closer than we
were 5 minutes ago.

• We got to find out what else is in the nucleus.
  That is why we go to part five.

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Do you remember Rutherford ?

• Rutherford continued to pry at the internal
  structure of the atom. By 1916 he is convinced
  that the positive part is not a jelly like mass
  of stuff. Rather his investigations lead to the
  idea that the positive electrical charge is
  created by a massive particle he calls the PROTON

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How much more ?

• More than you want to know.
• So we are only going to add just a few more
  parts.

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Enter James Chadwick

• Rutherford and his colleagues knew that the
  numbers they worked with just did not add
  up.(with respect to the size of the atom.) That
  is to say there had to be more inside the atom
  than what was being measured. Rutherford knew
  that there had to be a neutral substance inside
  the nucleus. He suggested the existence of the
  neutron in 1920. The particle should be the
  size of a proton, but since it carried no
  electrical charge, detecting it would be
  difficult. His friend James Chadwick looked for
  more than 10 years before he made the discovery.

Discovers the Neutron in 1932
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Inspiration comes when you least expect it.

• In 1930 two German scientists were experimenting
  with alpha particles. They noticed that a very
  powerful penetrating type of radiation was being
  produced. This radiation did not have any
  electrical nature. They assumed it was gamma
  radiation. Two years later, two French
  scientists were doing the same type of test,
  again thinking the radiation was gamma radiation.
  They discovered that protons were being released
  from a substance being bombarded with alpha
  particles. If gamma rays were doing this, then
  they would have to be more powerful than they
  were thought to be.
• Chadwick heard of the this activity and began a
  discussion with Rutherford. Both of these men
  came to the conclusion that the gamma radiation
  was not gamma radiation, but perhaps the long
  sought after neutral particle. This ray would
  have enough mass to knock away protons.

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Ive been workin like a dog.

• Chadwick worked as much as 20 hours a day for
  several months. After numerous tests the results
  were conclusive. The high energy particle being
  removed from his test substance was the elusive
  neutron. Experiments soon proved its total mass.
  Soon scientists had a good grasp on the basic
  structure of the atom.

Chadwicks neutron chamber
64
A really big part, but no juice. (Its
neutral)
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So what do we have so far ?

• The atom has a dense central area called the
  nucleus. Protons are found here.
• The nucleus has a powerful positive electrical
  charge.
• Electrons orbit the nucleus in energy levels, but
  can jump around in these levels. Each energy
  level is divided into four sub-levels called S
  P D F

• The electrons path around the nucleus is wave
  like.
• The position of the electron can never be known.
• Electrons absorb and loose energy quickly.
• The atom is heavier than the discovered parts so
  there must be more.

Yes
Is there any more ???
66

• The story of the discovery of the atom does not
  have a happy ending. Once the neutron was
  discovered and its properties were studied, it
  was quickly imagined that the neutron could be
  used to break apart other atoms and if done
  quickly, a tremendous amount of energy could be
  released. Einstein, in 1905, thought about such
  events. It inspired him to think about it
  mathematically. He discovered a very interesting
  math formula

From the Solar System atom to the Electron
Cloud atom.
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E mc2
A whole lot of energy from a little bit of matter
68
WOW !

• The atom has revealed its structure. Two main
  particles together in the nucleus. Also a small,
  but powerful particle orbiting this central
  region in a fashion that cannot be completely
  measured.
• The energy potential of the atom was wondered
  about and then proven to be greater than
  imagined.
• It took a war to pry into the deep reaches of its
  structure. Was a Pandoras box opened? Only time
  will tell.

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. That is something to think about

• The atom is unbelievably small. Yet it contains
  more energy than you or I can mentally
  understand. This energy can be controlled. If
  it is released quickly, then devastation results.
  If it is released slowly we can use it to
  generate power or harness it in other ways. It
  is our choice.

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It is up to us to understand this force and
control it. With your brains, we can make the
atom work for us.
Right ?
71
Right ?
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(No Transcript)
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Presentation Review
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Resource List.

• www.members.icanect.net
• www..com
• www.inetarena.com watertown.k12.wi.us
• www.levity
• www.nidlink.com
• www.accessexcellence.org
• www.pbs.org
• www.aip.org
• www.chembio.uoguelph.ca
• www.fordhamprep.com
• Check out these sites for more information.

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• There are so many un-named scientists in this
  story. There are too many events and ideas that
  have been glossed over. However, this is the
  story of how the basic structure of the atom was
  discovered.

• It is not the end of the story. These atomic
  parts have been further reduced into simpler and
  simpler parts. Each necessary for all the others
  to function. Complex, yet simple.
• Today the research story does continue.

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ITS WHATS INSIDE THAT COUNTS (KINDA)
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Aristotles ideas get twisted.

• Beginning about 100 AD the idea of nature seeking
  perfection was influencing the minds of men in
  the whole Mediterranean basin and throughout the
  Roman empire.
• Many had written about the art of
  transmutation or the changing of common metals
  into gold and silver. These writers basically
  create a new science that will come to be
  called ALCHEMY.
• History also records that in China, about this
  same time, a similar philosophy arose with
  accompanying practices. Here the gold was not for
  riches, but for health.

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Here is where it gets really weird.
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Amedeo Avogadro. Is it HO or H2O ? That is the
question

• 1811 this Italian scientist made some interesting
  discoveries that were not readily accepted at
  that time. He was forgotten about for 50 years,
  because he disagrees with Dalton. There is a
  distinction between an atom and a molecule.
  Molecules can split and join with other atoms to
  make new molecules. Like atoms can combine
• AA stated that the numbers of particles in equal
  volumes of gases at the same temperature and
  pressure were the same.This is celebrated every
  October 23rd with international mole day.

80
Electrons are in energy levels.

• Math models now prove that the electrons travel
  in changing wavelike paths around the nucleus.
  Energy gains and losses by the electrons effects
  the shape of the orbital.