P4 Atomic Structure
Development of The Model of The Atom
Overview
Atoms have a radius of 1x10-10m
Radius of nucleus < 1/10000 of the radius of the atom
All of the mass of the atom is concentrated in the nucleus
Protons have a mass of 1 and a positive charge, neutrons have a mass of 1 and no charge
Electrons
Electrons orbit the nucleus is energy levels (energy levels further from the nucleus are at a higher
level than those that are closer)
They can change energy levels if they gain energy but once the energy is emitted, they move back
History
1. D
e
m
o
c
r
i
t
u
s
450-370 BC
Everything made up of tiny solid spheres that were indivisible
2. Plum pudding model, Thomson 1904
Discovery of the electron 1897
Atom was a sphere of positive charge with tiny negative electrons stuck in them
3. Rutherford model 1911
Geiger and Marsden (1909), alpha scattering experiment to
test the plum pudding model
They fired alpha particles are gold foil
If plum pudding model was correct then the positive
charge inside the atom would be cancelled out by the
negative charge and the particles would pass through
The results: most went through but some were deflected
at extreme angles.
Conclusion: the atom was mostly empty space, most of its
mass was in the nucleus, nucleus was positively charged,
electrons orbit the nucleus
Alpha particles and gold foil both positively charged so repelled one another
4. Bohr model 1913
Electrons can orbit nucleus at specific distances
The further away an electron was from the nucleus the more energy it has
When an electron loses energy, electromagnetic radiation is emitted it moves down
When an electron gains energy, electromagnetic radiation is absorbed and it moves up
Development of The Model of The Atom
Overview
Atoms have a radius of 1x10-10m
Radius of nucleus < 1/10000 of the radius of the atom
All of the mass of the atom is concentrated in the nucleus
Protons have a mass of 1 and a positive charge, neutrons have a mass of 1 and no charge
Electrons
Electrons orbit the nucleus is energy levels (energy levels further from the nucleus are at a higher
level than those that are closer)
They can change energy levels if they gain energy but once the energy is emitted, they move back
History
1. D
e
m
o
c
r
i
t
u
s
450-370 BC
Everything made up of tiny solid spheres that were indivisible
2. Plum pudding model, Thomson 1904
Discovery of the electron 1897
Atom was a sphere of positive charge with tiny negative electrons stuck in them
3. Rutherford model 1911
Geiger and Marsden (1909), alpha scattering experiment to
test the plum pudding model
They fired alpha particles are gold foil
If plum pudding model was correct then the positive
charge inside the atom would be cancelled out by the
negative charge and the particles would pass through
The results: most went through but some were deflected
at extreme angles.
Conclusion: the atom was mostly empty space, most of its
mass was in the nucleus, nucleus was positively charged,
electrons orbit the nucleus
Alpha particles and gold foil both positively charged so repelled one another
4. Bohr model 1913
Electrons can orbit nucleus at specific distances
The further away an electron was from the nucleus the more energy it has
When an electron loses energy, electromagnetic radiation is emitted it moves down
When an electron gains energy, electromagnetic radiation is absorbed and it moves up
