Transcript Atomic Theory

Atomic Theory
The Atom

Recall the atom is the smallest
particle making up an element
Evolution of the Atom
Our ideas about the nature of atoms have progressed over
the last two centuries (and continue to develop today).
There are a few scientists who’s works have contributed
to our current knowledge of the atom.
JJ Thomson
MODEL
THOMSON (1900)
DIAGRAM

Year 1900

Discovered the electron

Thomson proposed raisin bun model…

Described the atom as positively
charged sphere of matter with negative
electrons dispersed throughout

electrons=raisins, positive mass=dough
Raisin Bun
Ernest Rutherford
MODEL
RUTHERFORD (1910)
DIAGRAM

Year 1910

Rutherford proposed the nuclear model….

Described the atom as having a central
positive nucleus (core) surrounded by
negative orbiting electrons
Nuclear Model
Proof?
Rutherford’s Famous
Gold Foil Experiment
A beam of positively charged alpha particles are aimed
at a thin sheet of gold foil (source radioactive radium)
Rutherford expected that the positive particles would pass
through the sheet of gold foil since years earlier Thomson
proposed that mass of the atom was evenly dispersed
throughout the atom.
MOST of the alpha particles did go straight through
the gold foil with NO deflection.
1.
However a small hand full of particles were deflected from
original path.
This could only happen if the the particles hit something that
had substantial mass and size and then bounced off at an
angle.
Rutherford’s experiment PROVED the presence of a dense,
positively charged core called the nucleus which was
surrounded by mostly empty space and orbiting electrons.
Niels Bohr
MODEL
BOHR (1911)
DIAGRAM

Year 1911

Bohr proposed the planetary model….

Nucleus (core) contains protons and
neutrons but electrons are located in
specific regions around the nucleus
1.
Solar System
Like planets are at a defined distance from Sun
In each of the 3 boxes on the lower half of your
sheet, make the following headings:
location charge symbol mass
Electron
Location
Charge
Symbol
Mass
orbitals
negative
e-
1/1800
amu
Proton
Location
Charge
Symbol
Mass
nucleus
positive
p+
1 amu
1 atomic mass unit (amu) = 1.67 x
-24
g
1 amu = 0.00000000000000000000000000000167 g
Proton
Location
Charge
Symbol
Mass
nucleus
neutron
n0
1 amu
1 atomic mass unit (amu) = 1.67 x
-24
g