Evolution of atomic theory

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