Transcript Atomic Theory Evolution

Atomic Theory
The Who’s Who of Atoms
Democritus
• ~460 BCE.
• Defined atom as the “smallest bit of
matter.
• 100 years later, Aristotle dismissed
his idea as “worthless.”
John Dalton
• 1805
• Said matter consisted of
elementary lumpy particles
• First Atomic Theory
• 5 Parts to his model:
Dalton’s Atomic Model
1. All matter is made of tiny particles
called atoms.
2. All atoms of one element are alike.
3. Atoms of one element are different
from atoms of other elements.
4. Compounds are formed when atoms
from different elements combine.
5. Chemical reactions involve rearrangement of atoms, not changes in
atoms themselves.
J.J. Thomson
• 1897
• Discovered the electron with his
Cathode Ray Tube Experiment
• Came up with the “Plum Pudding
Model” of atom
Cathode Ray Tube
Experiment
Plum Pudding Model
“Real” Plum Pudding
Max Planck
• 1900
• When you vibrate atoms enough
(heat it until it glows), you only get
energy in whole intervals: energy
packets called “quanta.”
Ernest Rutherford
• 1911
• Discovered the nucleus with his
Gold Foil Experiment
• Nucleus: the small, dense, positivelycharged center of the atom
• In 1919, he identified
“protons”
Rutherford’s Atom
Robert A. Millikan
• 1916
• Found charge and mass of electron
with his Oil Drop Experiment
Oil Drop Experiment
Niels Bohr
• 1912
• Developed planetary model of the
atom
• Discovered that electrons move
around the nucleus at set
distances
• Called these “electron
orbitals.”
Electron Orbitals
“Bohr Model” of the Atom
James Chadwick
• 1932
• Discovered the neutron
So Then We Have This!
Let’s Memorize These Guys!
• It’s the least we can do to
commemorate all their hard work!
• Quiz on Friday!
• 5 minute break? Then SUBATOMIC
PARTICLES!