The document traces the evolution of atomic theory from ancient Greek philosophers like Democritus, who proposed that all matter is made up of indivisible atoms, to modern scientists like Rutherford, Bohr, Thomson, Chadwick and others. Their experiments and findings progressively revealed more about the internal structure of atoms, including discovering the electron, nucleus, neutron, and that atoms are mostly empty space with electrons in motion around the dense nucleus. The current model depicts electrons in a probabilistic "electron cloud" rather than on fixed orbits as in the Rutherford-Bohr model.

1. The Evolution of The
Atomic Theory

2. Democritus
Lived: 460BC-370BC
Main concepts:
Everything is made of atoms
Atoms are indivisible (cannot be
divided)
Atoms are small and solid particles
Named the atom (called it “atomos”)

3. Dalton
Lived 1766-1844
Main concepts:
Each element has a different atom
and a different atomic weight
All atoms of the same element are
perfectly identical
Atoms cannot be created or
destroyed in chemical reactions.

4. Thomson
Lived: 1856-1940
Main concepts:
Discovered that atoms ARE divisible
Discovered the electron through his
Cathode-Ray experiment
Atoms have a much larger mass than
electrons
Inferred that atoms have a positive charge
Plum Pudding Model

5. Rutherford
Lived 1871-1937
Discovered that there is a small, dense
positively charged nucleus
Discovered that most of an atoms mass
is in it’s nucleus
Predicted the existence of neutrons
Stated that electrons move rapidly in
the empty space around the nucleus
Conducted the gold foil experiment
Stated that atoms are mostly empty
space.

6. Bohr
Lived 1885-1962
Stated that electrons can only travel at
specific distances from the nucleus
Stated that electrons can jump between
levels/paths around the nucleus
Stated that the chemical properties of
an element are determined by how
many electrons are in the outer shell.

7. Chadwick
Lived 1891-1974
Discovered the previously unknown part
of the nucleus of an atom- the Neutron!
Named the neutron because of it’s lack
of an electrical charge.
His discovery made it possible to create
new elements in the laboratory (heavier
than Uranium) which was not possible
before.

8. Electron Cloud Model
This is our most modern and
accepted model of the atom
It differs from Bohr’s model
because it states that the electrons
can be found in a general region
around the nucleus, not specific
paths.

9. Time for:
The atom song!
http://www.youtube.com/wat
ch?v=vUzTQWn-wfE

10. Time for:
The atom song!
http://www.youtube.com/wat
ch?v=vUzTQWn-wfE