The History of the Atom

1
The History of the Atom.

• Democritus was the first to theorize that all
  matter was composed of atoms!
• The name atom comes from his Greek word,
  atomos, which means not dividable or whole!
• Democritus ideas were crushed by a another Greek
  Philosopher, named.

2
Aristotle!!!!

• Aristotle asked Democritus three questions
• If we are made of atoms, what holds us together?
• Why cant we see these atoms?
• Why dont we fall down like a bag of marbles?

3
Democritus was unable to answer these questions.

• And so, people continued to think that matter was
  continuous - your body, the world around us was
  one continuous piece.
• This philosophy continued for centuries.

4
During the middle ages, science was lost to the
world

• The only science that was done was performed by
  Arabs (Moors) out of Africa that conquered Spain!
• They traveled from the Middle East to Western
  Europe, carrying the great library of Alexandria
  with them!
• While the plague and the dark ages were killing
  millions, they had..

5
EVERYTHING..!

• Running water..
• Dentistry..
• Reading, Writing, Geometry, Calculus
• Breweries.
• Complex gardens and Agriculture..

6
Science did not start up again until the Church
was challenged.

• The church was preventing people from coming up
  with new ideas and doing science!
• Who were some people that challenged the Church?
• Once the Church is challenged by thinkers,
  science experiments start to be done!
• With independence, came independent thought and
  ideas..

7
During the 1700s and 1800s.

• Scientists were discovering concepts and
  relationships
• Scientists were doing large, observable, basic
  experiments
• They werent doing tests with microscopes or
  computers!
• They were doing experiments with stoves, pots,
  ovens, and basic glassware!
• With observable properties came explanations!

8
Joseph Priestley.

• Prepared pure Oxygen
• Decomposed mercuric oxide into mercury and oxygen
• Invented soda pop
• Discovered carbon dioxide and nitrous oxide
  (laughing gas)

9
Priestley noticed that the gas produced by
heating mercuric oxide burned a candle brightly.

• He called the air, perfect air, or
  dephlogisticated air
• People thought that phlogiston was a substance
  that was in materials
• When substances burned, they released phlogiston,
  which eventually caused flames to go out.
• Is this true.?
• He had actually discovered oxygen, but didnt
  realize it!

10
Antoine Lavoisier..

• Lived during the French Revolution
• Was a brilliant scientist, but a tax collector
• Had his head chopped off during the revolution
  with royalty

11
Lavoisier Proved..

• That substances did not give off phlogiston, but
  used oxygen!
• He burned metals in the air, and weighed them
  before and after
• The substances weighed more after, because they
  were combining with oxygen, not giving off
  phlogiston!

12
By weighing the materials before and after..

• Lavoisier came up with..
• The law of Conservation of Mass
• This states - Matter cannot be created or
  destroyed in a chemical reaction, simply
  converted from one form into another
• The extra mass came from the oxygen in the air,
  which he later measured by reheating the compound
  formed

13
Joseph Proust..
This compound is always 5.3 parts Cu, 4.0 parts
O, and 1.0 parts C!

• Examined copper carbonate
• No matter the amount, whenever decomposed it
  would yield 5.3 parts copper, 4.0 parts oxygen
  and 1.0 parts carbon
• Came up with the law of definite composition
• All substances are composed of definite amounts
  of each element, no matter how much or how little
  of the matter there is!

14
John Dalton

• A schoolteacher!
• Devised the Law of Multiple Proportions
• Stated that when two elements form more than one
  compound, they come together in whole number
  ratios

15
WHAT DOES THAT MEAN?

• Carbon and Oxygen form two compounds
• Carbon dioxide - C1O2
• Carbon monoxide - C1O1
• In carbon dioxide, C1O2, carbon and oxygen
  combine in a 3 parts to 8 parts mass ratio
• In carbon monoxide, C1O1, they do so in a 3 parts
  to 4 parts mass ratio..
• Seem obvious.?

16
IT WASNT

• Scientists didnt know what was making things
  come together to react!
• In fact, They didnt even know that atoms
  existed!
• If compounds come together in ratios, they must
  be made of smaller pieces!

17
John Dalton theorized that these substances were
made of atoms!

• This led to.
• THE ATOMIC THEORY OF MATTER!
• All elements are made of tiny, solid,
  indestructible particles known as atoms
• All atoms of a given element are the same
• Atoms of different elements are different
• Atoms of different elements form compounds in
  whole number ratios - 1 atom 1atom, 1 atom 2
  atoms, etc.
• A chemical reaction does not change the atoms
  themselves, only how they are combined to form
  compounds

Br
H
I
Fe
S
18
It took almost 2000 years before the idea of the
atom came back!

• John Dalton brought Democritus idea back!
• It seems simple, but people did not believe that
  matter was made of little marble-like structures
  called atoms!
• John Daltons theory was wrong in one respect..

19
Atoms are not solid and indestructible like
marbles..

• They contain different parts.
• However, scientists did not know this until parts
  of the atom were discovered..
• What part of the atom do you think was discovered
  first..?

20
THE ELECTRON!

• Why do you think it was the first part of the
  atom to be discovered..?

21

• The electron is on the outside of the atom!
• The electron is the ONLY part of the atom that
  can be added or removed to an atom!
• The electron is tiny and light, and that is why
  it can be added or removed!
• This is what we call electricitymoving
  electrons!
• Technology wasnt that good hundreds of years
  ago!

e- e- e- e- e- e- e- e- e-
22
The Early 1800s!

• Lots of basic work with electricity
• Matter has charge!
• There are two types of charge in the world
• charged objects
• - charged objects
• Ben Franklin is the first to come up with these
  names - and -
• Franklin didnt know that these
• charges were part of the atom -
• he didnt even know that atoms
• existed, yet!

23
Cathode Ray Tube, or Crookes Tube

• This was one of the very first experiments to be
  done with electricity!
• A tube containing two metal electrodes or plates
  connected to a battery - and all of the gas is
  sucked out of the tube!
• William Crookes designed this tube in 1879
• The cathode ray inside glows green
• Crookes was convinced this beam consisted of
  charged particles

24
So what are Cathode Rays.?

• J.J. Thomson, in 1897, answered this question!
• Thomson used a Crookes tube and two charged
  plates above and below the beam
• Which way do you think the beam bent.?
• The Beam was attracted to plate, and was
  deflected from plate!
• From this, he said that the beam was made of
  negatively charged particles, called electrons!
• He was looking at electrons, which are part of
  the atom!
• These electrons can be easily taken off of atoms,
  and used as electricity!

25
He also found that a magnet could move the beam
as well!
26
The cathode ray tube was the beginning to the
modern day..
TELEVISION!
Black and White..
Color.
27
Millikan Oil-Drop Experiment

• Robert Millikan in 1909 figured out the exact
  charge and mass of an electron
• He placed oil drops in a box, and hit them with
  electrons
• The oil drops were sprayed into the upper chamber
• Some drops gained charge (static electricity)

28

• Then Millikan adjusted the charge on the plates
  in the bottom of the box
• The - particles attracted to the upper plate,
  because it was positive
• It repelled the bottom plate, because it was
  negative
• This suspended the drop in space- he made them
  float in mid air!
• From this he calculated the charge and mass of an
  electron, knowing the charge on the plates
• The smallest change between two drops was taken
  to be charge of an electron

-
29
Now that we have found negative particles.

• Eugen Goldstein in 1886 used a Crookes tube with
  holes in the negative end and discovered positive
  particles
• He shot a cathode beam (beam of electrons) at
  hydrogen atoms

30

• The electrons from the atoms went with the beam
  of electrons to the plate
• He also saw particles moving backwards towards
  the plate and going through the holes!
• He named these particles protons!

31
Who puts all of this information together into
The Big Picture?

• J.J. Thomson theorized that these negative and
  positive particles were actually part of matter -
  part of the atom!
• We are all made of charge!
• He develops the first working model of the atom,
  known as the PLUM PUDDING MODEL!
• This rejected Daltons idea that atoms were solid
  particles like marbles that werent made of
  smaller pieces

NOT TRUE!
32
Why was any of this IMPORTANT?

• People didnt believe in atoms, and didnt
  understand what things like electricity and light
  were!
• Thomson showed that electricity was nothing more
  than a flow of little negative particles called
  electrons!
• And electrons, along with protons, make up every
  atom, in every person, plant, building and object
  in the universe
• We are made of charged particles - the same
  particles that we use for electricity!

33
Why is Thomsons model wrong.?

• A scientist named Ernest Rutherford figured it
  out!
• He shoots big heavy alpha (?) particles at ultra
  thin gold foil
• Most of the particles went straight through, and
  did NOTHING.
• A very few were deflected, and some even bounced
  straight back!
• Rutherford described this as a bowling ball being
  sent at a piece of paper, full speed, and
  bouncing back!

34
The Gold Foil Experiment.
What is happening? Why are the alpha particles
bouncing off?
35
Gold Foil Experiment..
36
What is going on.?

• Most of the alpha particles are going straight
  through!
• A few of the alpha particles are bouncing off of
  something!
• Alpha particles are big, and positive!
• What could they be bouncing off of?
• They must be bouncing off of something that is.
• Positive!
• And big!
• Rutherford theorized that all of the protons
  werent scattered about, like in a chocolate chip
  cookie, but were all concentrated into a tiny,
  dense center, which he called the nucleus!
• The electrons must be orbiting around this
  nucleus! Why?????

37
Rutherfords nuclear model!
38
What is the relative size of the atom.?

• An atomic model the size of Busch Stadium and
  parking would contain a pea sized nucleus
  containing 95.95 of the atoms mass.
• The pea at the pitchers mound would be the
  nucleus, and an ant crawling on the parking lot
  outside would be an electron!
• The atom is mostly..
• Empty space! Nothing!

39
So is this the final model of the atom today?

• No!
• A scientist named Neils Bohr, a great friend of
  Einstein, noticed something weird about Hydrogen
• A hydrogen atom consists of 1 electron orbiting 1
  proton.
• Atoms can give off light when they are excited
  with electricity!
• Think about light bulbs, neon lights,
  headlights.
• With one electron, how many different types of
  energy or colors of light do you think hydrogen
  can give off.?

40
. Only one color of light!

• Bohr excited hydrogen atoms with high voltage
  electricity
• Hydrogen gave off violet light.
• The violet light was actually FOUR DIFFERENT
  COLORS OF LIGHT, as viewed through a prism
• How can one electron give off four colors of
  light???

41
HOW IS THIS POSSIBLE?

• It doesnt make sense that one electron can give
  off four different colors of light!
• Hydrogen, with only one electron, should be
  giving off just one color!
• Bohr came up with an explanation for this.
• It involved changing the current accepted model
  of the atom!

42
Bohr came up with a new model for the atom

• Bohr suggested that it electrons could move to
  many locations or energy levels within the
  atom!
• The electron was moving to more than one location
  in the atom!
• In Bohrs Model of the atom, electrons orbit the
  nucleus like planets orbit the sun. It is called
  THE PLANETARY MODEL.
• When electrons jump up to different energy
  levels, they eventually fall back down and give
  off light!

43

• Electron can jump up, and when they fall back
  down, they give off colors of light!

44
The colors we see for Hydrogen
45
Different substances give off different
colors.Why?
46
Different elements have different electrons, that
can jump to different places in the atom!
Carbon
Helium
Neon
47
(No Transcript)
48
Electrons in Energy Levels

• Level maximum number of electrons
• 1 2
• 2 8
• 3 18
• 4 32

49
Another problem with the puzzle.

• Werner Heisenberg, a famous German scientist,
  suggested that it was impossible to know exactly
  where an electron was at all times!
• To watch an electron orbit the nucleus would
  require light!
• Shining light on an electron might do what.?
• Move it!
• And electrons are so small, and move so fast,
  that we would lose where it would go!
• The Heisenberg Uncertainty Principle It is
  impossible to simultaneously know an electrons
  location and speed around the nucleus of an atom.

Photon of light
Unknown new location
50
So what does THAT mean???

• Electrons travel around the nucleus, and we cant
  be sure where they are some of the time!
• Erwin Schrodinger used complicated mathematics
  and probability to calculate where electrons were
  most likely to be located.
• This new model, called the Quantum Mechanical
  Model predicts the probability of where the
  electron is going to be 90 of the time!
• It is also called the electron cloud model or the
  90 probability model!
• It means that we THINK that the electron is
  located in some region or cloud of space, 90
  of the time! But if we went looking for it by
  shining light on it, it might move to some
  unpredictable location!

51

• A model where we dont know where the electron
  is???
• But Schrodinger did calculations to figure out
  exactly where in the energy levels we could
  probably find the electron.
• These locations were called sublevels.
• Even within these sublevels, Schrodinger figured
  out what shape an electron would be located in
  when it movedcalled an orbital!
• So remember, electrons dont travel in nice
  circular orbitsthey travel in unpredictable,
  wavelike patterns in a 3-dimensional area.These
  areas are called sublevels..the electron could
  be there at any time! It would be like taking a
  snapshot picture.The orbital is a collection of
  all of the potential snapshots

52
Why do we care about where the electrons are so
much???

• The electrons are the outside part of the atom!
• They are the only part of the atom that can be
  added or removed!
• They are what make an atom react! Where they
  are has everything to do with how an atom will
  react!

53
s, p, d, and f Sublevels
Insert figure 5.31
54

• Some hints.
• Any energy level n has exactly n sublevels in
  it
• Each sublevel has a specific number of orbitals,
  as seen on the chart below
• Since electrons dont like each other, having the
  same charge and repelling each other, an orbital
  can
• hold a maximum of only 2 e-. This is known as
  the Pauli Exclusion Principle.
• Remember - a sublevel simply tells us where an
  electron is located, and an orbital tells us
  something
• about the shape that it moves within as it
  travels in a wave!

8
18
n sublevels names 1 1 s 2 2 s,
p 3 3 s, p, d 4 4 s, p, d, f 5 4 s, p,
d, f
55
Who wants to draw complicated atoms with these
sublevels and orbitals included in the picture?

• Instead, we can use shorthand for where the
  electrons are located!
• There are two shorthand ways of indicating where
  electrons are located
• Electron Configurations
• Orbital Diagrams
• Lets look at each and discuss why we use them!

56
Electron Configurations

• We use this shorthand to indicate where electrons
  live
• We use numbers to indicate the energy level,
  letters to indicate the shape or sublevel, and
  superscripts (exponents) to indicate how many
  electrons there are in a particular sublevel!
• For example, Lithium would be written as
• Li 1s22s1
• Notice there are 3 electrons total - 2 electrons
  in the s sublevel of the 1st energy level, and 1
  electron in the s sublevel of the 2nd energy
  level!

of electrons
Li 1s22s1
sublevel
energy level
57
What energy level would an electron fill first?

• The lowest possible energy level, of course!
• Electrons are negative!
• They want to be as close to the nucleus as
  possible!
• This is the lowest energy, most stable location..
• This is known as the Aufbau Principle
• Electrons fill lowest energy levels first!
• Can we write the electron configuration for
  sodium, then?
• Sodium has.
• 11 electrons!
• We know that electrons would first occupy the
  first energy level!
• Once that is filled, they would then fill the
  second, and then the third, etc.
• Na 1s22s22p63s1

58
Inverted Triangle Apartment Building
Floor n Apt orbital (s, p, d, f) s 1
bedroom 2 e- p 3 bedroom 6 e- d 5 bedroom
10 e- f 7 bedroom 14 e- (2 e- per room)
59
Electron Configurations
Notice the violation of the Aufbau Principle.
60
Electron Configurations

• 7s 7p .. .. .. .. ..
• 6s 6p 6d 6f .. ..
• 5s 5p 5d 5f ..
• 4s 4p 4d 4f
• 3s 3p 3d
• 2s 2p
• 1s

• Look at potassium
• 19 electrons
• You would think its configuration would be
• K 1s22s22p63s23p63d1
• Instead, it is
• K 1s22s22p63s23p64s1
• This is known as a violation of the Aufbau
  Principle!
• Why would an atom DO THIS????

61
Insert figure 5.36
62
The second way to show where electrons are
located is called an orbital diagram

• This is a better way of actually seeing where
  electrons are!
• We draw square boxes to indicate sublevels.
• We draw up and down arrows to indicate electrons
• Oxygen would be written like this.

An orbital diagram.
O

• Each box represents a shape - a sphere, a figure
  8, etc.
• Notice anything weird about this?
• The last two electrons filled separate orbitals
  first!
• Why would they fill separate p orbitals first,
  instead of just going into the same orbital?
• Electrons repel each other, and want to stay as
  far away from each other as possible!
• This is known as Hunds rule - electrons fill
  singly occupied orbitals first!

63
Marble Model
Plum Pudding Model
The Nuclear Model
The Planetary Model
64
Why is learning about the atom important.?

• The atom was considered to be an imaginary
  thing, something that people laughed at!
• Roosevelt trusted Einstein, and funded his secret
  research known as the Manhattan Project
• In a few short years, the idea of an invisible
  atom had been developed into a city-destroying
  weapon - the atomic bomb! They figured out they
  could split atoms apart, and this would release
  tons of energy!

65
In Hiroshima, of a resident civilian population
of 250,000 it was estimated that 45,000 died on
the first day and a further 19,000 during the
subsequent four months. In Nagasaki, out of a
population of 174,000, 22,000 died on the first
day and another 17,000 within four months. Over
90 of each city was destroyed.
Only two atomic bombs have ever been used in
wartime history - The U.S. used them both against
Japan to end World War II.
The first video shows one of the actual bombs
being detonated.The second, the first testing of
a Hydrogen Bomb