History of Elementary Particles
• Greeks invented concept of Atom approximately 2500 years ago
• Later thought matter was made up of fire,water,air,earth
Definition of Atom: Smallest particle of an element that retains the chemical identity of the
element
Let’s call it … an atom.
400 B.C
0
1700 A.D.1492 A.D.
Columbus Discovers the
West
Greeks invent concept of atom
About late 1700s some new ideas through experiments came to be discussed.
What Were Some of the Results of These Experiments?
• Law of Conservation of Mass
• Law of Constant Composition (also called Law of Definite Proportions)
• Law of Multiple Proportions
Law of Conservation of Mass
• Matter is not created or destroyed in a chemical reaction
+ =
Law of Constant Composition or Law of Definite Proportions
A chemical has exactly the same proportions no matter the size
Example: Doesn’t matter if 3 crystals or
a jar of salt 66 % of mass is always
Chloride 33 % of the mass is always
Sodium
OR
Same “Proportions”, Same “Composition”
Example of the Law or Constant Composition (Law of Definite Proportions)
What would happen if I take a small bite of cake or a GIANT bite of cake?
Would it taste the same? The “Composition” of the cake is
the same all the way through. A COMPOUND (like sugar or salt)
is the SAME no matter where you find it, or how much you have.
The Law of Multiple Proportions
Chemicals always combine in ratios of small whole numbers
Example: H2O - Water There will always be a 2 to
1 ratio between Hydrogen and Oxygen
Whether you have one water molecule or an ocean full water
Law of Multiple Proportions Example
Molecules are not made up of “1/2” or an atom or pieces of an atom
This proportion might be 1: 3/4
Remember WHOLE numbers.
400 B.C0
Late 1700s
1492
A.D.
Columbus
Discovers the West
Greeks invent concept of atom
John Dalton and the Atomic Theory of
Matter
New Experiments and Laws
1803
QuickTime™ and aTIFF (Uncompressed) decompressor
are needed to see this picture.
• At age 12 Dalton was teaching the local school
• Was reading Newton’s Book in Latin
• Color Blindness was called “Daltonism” for a lengthy time
QuickTime™ and aTIFF (Uncompressed) decompressor
are needed to see this picture.
John Dalton - 1803Atomic Theory of Matter
• UNIQUE - Atoms are unique from other elements
• GROUPS - Compounds are combined in small whole numbers.
• LAW OF CONSERVATION OF MATTER - atoms are rearranged or combined but not destroyed
• INDIVIDUALS - Elements are composed of atoms (smallest building block)
QuickTime™ and aTIFF (Uncompressed) decompressor
are needed to see this picture.QuickTime™ and a
TIFF (Uncompressed) decompressorare needed to see this picture.
QuickTime™ and aTIFF (Uncompressed) decompressor
are needed to see this picture.
400 B.C0
Late 1700s
1492
A.D.
Columbus
Discovers the West
Greeks invent concept of atom
John Dalton
and the
Atomic Theory
of Matter
New Exper-iments and Laws
1803
QuickTime™ and aTIFF (Uncompressed) decompressor
are needed to see this picture.
Almost 1900
QuickTime™ and aTIFF (Uncompressed) decompressor
are needed to see this picture.
Thompson Discovers the Electron
John Thompson, circa 1900 Discovers Electron
• Prior to this a man named Faraday hypothesized that atoms had a charge
• Thompson hypothesized that the electrical charge was negative and that the particle had mass
QuickTime™ and aTIFF (Uncompressed) decompressor
are needed to see this picture.
Thompson’s Experiment using a Cathode Ray Tube (CRT)
• Elements are neutral (no charge)
• Thompson could alter path of particles by using magnets (that showed they had a charge)
• The type of magnet showed that it had a negative charge
QuickTime™ and aTIFF (Uncompressed) decompressor
are needed to see this picture.
battery magnets
Thompson (continued)
• Now Thompson knew that there was a negative particle in the atom but where???QuickTime™ and a
TIFF (Uncompressed) decompressorare needed to see this picture.
QuickTime™ and aTIFF (Uncompressed) decompressorare needed to see this picture.
I’m tired…
400 B.C0
Late 1700s
1492
A.D.
Columbus
Discovers the West
Greeks invent concept of atom
John Dalton
and the
Atomic Theory
of Matter
New Exper-iments and Laws
1803
QuickTime™ and aTIFF (Uncompressed) decompressor
are needed to see this picture.
Almost 1900
QuickTime™ and aTIFF (Uncompressed) decompressor
are needed to see this picture.
Thomp-son Dis-covers the Electron
QuickTime™ and aTIFF (Uncompressed) decompressor
are needed to see this picture.
Rutherford discovers the nucleus
1910
• Rutherford was not a brilliant man, often getting lost in Math, not terribly clever in experimentation, just tenacious and open-minded
• His assistant was Hans Geiger, inventer of the “Geiger Counter”
QuickTime™ and aTIFF (Uncompressed) decompressor
are needed to see this picture.
Rutherford’s Model of the Atom
QuickTime™ and aTIFF (Uncompressed) decompressor
are needed to see this picture.
QuickTime™ and aTIFF (Uncompressed) decompressor
are needed to see this picture.
Yum Yum!
Rutherford hypothesized that the inside of an atom was a mass with bits of matter mixed in.
He called the model the
“Plum Pudding”
Model
Rutherford’s Gold Foil Experiment
• Rutherford set up very thin gold foil as a target
• “shot” positive charges to foil
• Watched patterns that positive particles made
QuickTime™ and aTIFF (Uncompressed) decompressor
are needed to see this picture.
Results of the Rutherford’s Experiment
• Alpha particles (positive particles) went through
• Only sometimes ‘bounced” back
• Proved that nucleus was mostly empty space
• Called center “nucleus”
QuickTime™ and aTIFF (Uncompressed) decompressor
are needed to see this picture.
Rutherford’s NEW Model of the Atom
QuickTime™ and aTIFF (Uncompressed) decompressor
are needed to see this picture.
QuickTime™ and aTIFF (Uncompressed) decompressor
are needed to see this picture.
Yuck!
Rutherford hypothesized that the inside of an atom was a small mass called a nucleus.
Rutherford’s Gold Foil Experiment Animation
http://micro.magnet.fsu.edu/electromag/java/rutherford/index.html
What Do I Need to Remember ?
• Greeks came up with Atom• 3 Laws that started it all…• Dalton - Atomic Theory of Matter• Thompson CRT Experiment• Rutherford’s Gold Foil Experiment
Memory Helps
• Rutherford– A Ford Truck carrying
– Plum Pudding
– Covered in Gold Foil
– Discovered the Nucleus
QuickTime™ and aTIFF (Uncompressed) decompressor
are needed to see this picture.
I’d “Rather” have a Ford (Rutherford)
3 Laws
One You Already Know…
Always
Whole #s
Law of Conservation of Matter Law of Definite
Proportions Law of Multiple Proportions
Thompson Cathode Ray Tube
QuickTime™ and aTIFF (Uncompressed) decompressor
are needed to see this picture.
Daltons Theory of Matter
• UGLI– U Unique (Elements are..)
– G Groups (They are grouped in small whole number groups Law of Multiple Proportions)
– L Law of Conservation of Matter
– I Individual (Matter is made up of individual atoms)
QuickTime™ and aTIFF (Uncompressed) decompressor
are needed to see this picture.