Physsssssssssics

1. FUNDAMENTAL Physics – Atomic Physics: 7.1 The Nuclear Atom
The Atom
http://www.youtube.com/watch?v=DwqYsoDqbCQ
Learning Objectives
• I can describe the Geiger-Marsden Experiment
• I can describe how these results explain Rutherford’s Model of the nuclear
atom
• I can define a nucleus in terms of Proton Number and Nucleon Number
• I know how ISOTOPES occur
• I know that some isotopes are UNSTABLE and undergo a RANDOM process
of radioactive decay
• I know that Alpha, Beta and Gamma radiation is emitted when an unstable
nucleus decays
• I know the nature of Alpha, Beta and Gamma radiation and their defferent
penetration
The Scientific Process
Phenomena → hypothesis → prediction → investigate/experiments → theory
→ Law
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2. FUNDAMENTAL Physics – Atomic Physics: 7.1 The Nuclear Atom
Earlier Models of the Atom; JJ Thompson – Plum Pudding
Geiger-Marsden Experiment – Alpha Particle Scattering by a Gold Foil
The results of this experiment were:
• The large majority of the alpha particles go straight and are not deflected
• A small number of alpha particles are deflected through a small angle.
• A very small number of alpha particles are deflected through a large angle
(rebound)
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Florescent screen
Large majority of
flashes occur
straight ahead
Small number of α
particles are deflected
Very small number of
α particles deflected
at a large angle

3. FUNDAMENTAL Physics – Atomic Physics: 7.1 The Nuclear Atom
Rutherford’s Model of the Nuclear Atom
The observations from the Geiger-Marsden experiment
were used by Rutherford and led him to propose the
theory of the nuclear atom.
Observation from the
Geiger-Marsden Experiment
Hypothesis proposed by Rutherford
Large majority of the α particles go
straight through the gold leaf
Most of an atom is ......... space and
therefore the mass of the atom must be
held in a small region, called the ..........
Some of the α particles are
scattered.
No useful hypothesis can be considered.
A very small number of positively
charged α particles undergo LARGE
ANGLE SCATTERING. (repelled back
through more than 90o
)
There must be a …….., …………… charged
nucleus, that contains almost all of the
………….. of the atom.
Other advancements (not required):
• Niels Bohr postulated the quantum energy levels of the electrons.
• 1932 Neutrons discovered by James Chadwick.
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4. FUNDAMENTAL Physics – Atomic Physics: 7.1 The Nuclear Atom
What Affects the Scattering of the Alpha Particles (required)
What affects the amount of deflection?
1. Charge – the alpha particles are positively charged that is why they
experience ............... from the ............ charged nucleus.
2. Speed – Particles B and F are moving ............... than particle A. They
experience a smaller deflection because they spend ........... time close to
the nucleus.
3. Proximity to the nucleus – only the very small number of alpha particles
that pass very close to the ............. experience enough repulsion for ‘large
angle scattering’ such as particle D.
The Rutherford-Bohr / Standard Model of the Atom
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5. FUNDAMENTAL Physics – Atomic Physics: 7.1 The Nuclear Atom
5
Positive
protons
Neutral
Neutrons
Negative
electrons

6. FUNDAMENTAL Physics – Atomic Physics: 7.1 The Nuclear Atom
Atomic Symbols
Eg. Carbon
Z for example 6 is the proton number / atomic number, which is the number of
protons in the nucleus. The proton number defines the element.
A, for example 12 is the mass number / nucleon number which is the number of
protons plus neutrons in the nucleus.
Isotopes
A given element is defined by the given number of protons. However the number
of neutrons can change. An isotope is different version of the same ……….. that
has a different number of …………….
Radio-isotopes
Since neutrons play an important role in binding the nucleus together, too ………
or too ……… neutrons will affect the stability of the nucleus.
A radio-isotope has an unstable nucleus that can, at any moment, decay in order
to try and achieve stability.
6
C
12
6
C
A
Z

7. FUNDAMENTAL Physics – Atomic Physics: 7.1 The Nuclear Atom
Radioactive Decay
Decay is a random process by which an alpha or beta particle or a gamma photon
is emitted from an ………….. nucleus which is trying to become stable.
Radioactive Particles
http://www.youtube.com/watch?v=N8JRqW1-my4&NR=1
http://www.youtube.com/watch?v=9j62CVRwZPc
Name Symbol Nature Sources Ionising
Power
Penetratio
n
Stopped
by
Range
in air
Alpha α
………..
Nucleus
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He2+
Larger
nuclei
Eg.
208
Po
High Low ……… 2-3cm
Beta β
An ………
-1β-1
smaller
nuclei
eg. 40
K
Medium Medium
1-2cm
of ……..
Few
feet
Gamma γ
An EM
wave. A
packet of
…….
called a
PHOTON.
Eg. 99
Tc
low high
Several
inches
of …….
kms
Homework Page 253 Q 1-4
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8. FUNDAMENTAL Physics – Atomic Physics: 7.1 The Nuclear Atom
For this topic please make use of www.furryelephant.com which has many electricity
animations and explanations.
School username: islandschool
School password: islandscience
This was expensive, but it is very very good.
The Wall
http://www.youtube.com/watch?v=M_bvT-DGcWw
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