Download Democritus - The Laughing Philosopher

What are important discoveries
related to the structure of an atom?
• Three sub-atomic particles:
• Atom – basic unit of matter
• Element –substance consisting of one type of
atom
• Compound – substance consisting of two or more
different atoms
Democritus
The Laughing Philosopher
- Matter composed of atoms (tiny
indestructible units)
- No experiments, Little evidence
- Smooth (sweet) and sharp (sour)
atoms
John Dalton 1808
Dalton's Atomic Theory
1) Matter is made of atoms
which are indivisible and
indestructible.
2) All atoms of an element
are identical in mass and
properties.
3) Compounds are formed by
two or more different kinds
of atoms coming together.
4) A chemical reaction is a
rearrangement of atoms.
JJ Thomson 1897
• Lots of positive space
with negative clusters
• Cathode Ray Experiment
• Discovered electrons
• Plum Pudding Model
• Chocolate Chip Muffin
What is plum pudding?
Ernest Rutherford
1908
• Atoms= mostly empty space
• Discovered nucleus that
contained positively charged
particles
• Gold Foil Experiment
• Particles were deflected
• Electrons circle nucleus
Robert Millikan
1909
• Oil Drop Experiment
• Calculated mass and charge
amount of electron
Flea
on a
Elephant
Neglible
Zero
Mass
Neils Bohr 1913
• Electrons move in orbitals
(energy levels) around nucleus
• Like planets and the sun
• Each orbital holds a certain
number of electrons
James Chadwick
1932
• Discovered neutrons
• Neutral particle with mass
close to proton
Current Model
• Watch “Atomos, Atomos” Video
• Watch Rutherford's Gold Foil Experiment