History of Elementary Particles. Greeks invented concept of Atom approximately 2500 years ago Later thought matter was made up of fire,water,air,earth

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


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



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)


are needed to see this picture.QuickTime™ and a

TIFF (Uncompressed) decompressorare needed to see this picture.



400 B.C0

Late 1700s

1492

A.D.

Columbus

Discovers the West


John Dalton

and the

Atomic Theory

of Matter

New Exper-iments and Laws

1803



Almost 1900



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



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



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


John Dalton

and the

Atomic Theory

of Matter

New Exper-iments and Laws

1803



Almost 1900



Thomp-son Dis-covers the Electron



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”



Rutherford’s Model of the Atom





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



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”



Rutherford’s NEW Model of the Atom





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



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



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)



Documents

History of Elementary Particles. Greeks invented concept of Atom approximately 2500 years ago Later thought matter was made up of fire,water,air,earth