Download 25 The Atom - SJHS-IB

7: Atomic and Nuclear
Physics
7.1 The Atom
Atomic Theory
The Plum Pudding Model
Negative charged
electrons
Positive charged
mass
Rutherford’s Alpha Particle Scattering Experiment
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Results
Rutherford found out that...
1. Most of the alpha particles passed through the
gold foil undeviated.
2. A few alpha particles were deflected from their
path but continued through the gold foil.
3. A small number of alpha particles rebounded.
Conclusions
1. As most alpha particles passed through the gold
foil atoms undeviated, Rutherford concluded that
most of the atom was actually empty space.
2. The deviation of some alpha particles from their
original path were due to positive charges within the
foil.
3. A very small number of alpha particles had
rebounded because they collided with something
with a much bigger mass, which contains a
concentrated region of positive charge. This is now
called the nucleus .
The Rutherford - Bohr Model of the Atom
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n
Energy Levels
E = hf
h
= Planck constant
= 6.6 x 10-34 m2kgs-1
E.g.
hf = E2 - E1
Emission Spectra (Line Spectra)
Hydrogen...
Helium...
Neon...
Limitations of the Bohr Atom
Electron ‘probability cloud’:
The Nucleus
Any nuclide can be represented in the following
way:
A
Z
X
A = nucleon number
Z = proton number
X = symbol for the element
N = neutron number
Q. Nucleons must experience a force other than
electrostatic force. Why?
Isotopes
Nuclide: an atomic nucleus with a particular
combination of protons and neutrons.
Isotope: Atoms with the same number of protons
but different numbers of neutrons.
E.g.1
35
37
17
17
E.g.2
Hydrogen
Deuterium
Tritium
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