Getting Inside the Atom

1
Getting Inside the Atom

• Who were the people that first imagined what
  atoms looked like?
• What experiments gave clues about what atoms look
  like?
• What did our early models of atoms looks like?

2
Greeks Atomos Model(400 BC)

• 4 Elements
• Earth
• Wind
• Water
• Fire
• Atomos
• Smallest possible piece of something

3
John Dalton Billiard Ball Model (1803)

• Gases combine in fractions
• Example
• 2 parts H 1 part O ? water
• Mass before Mass after
• Atoms are different sized
• hard spheres that join

O
Water (H2O)
H
H
4
JJ Thomson Plum Pudding Model (1897)

• High voltage gases emit cathode rays that are
• attracted near magnets or electrically charged
  plates
• light weight (much less than atoms)
• Atoms have electrons inside

positively charged atom electrons
O

Water (H2O)


H
H
5
Ernest Rutherford Nuclear Model (1910)

• Send radioactive alpha particles into material
• Expected them to go quite straight
• Some deflected towards side
• A few deflected backwards
• Atoms contain a heavy
• central nucleus

positively charged nuclei electrons
O
Water (H2O)

H
H


6
How Hard Was Rutherfords Experiment?

• How small is the nucleus compared to the atom?
• Ball in ball point pen nucleus
• Classroom atom
• Atoms are mostly empty Space!
• Can you detect the nucleus?
• Shoot rubber bands at ball point pen
• If you ring it you have discovered the nucleus!
• If you miss the nucleus remains undiscovered today