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Previous Theories About The
Atomic Structure
· 5th BC - Democritus: He believed that all matter was made up
of identical lumps called "atomos".
· 1804 ­ John Dalton: Agreed with Democritus that matter was
made up of tiny spheres that couldn't be broken up but he also
thought that each element was made up of a different type of
"atom".
· 1900s ­ JJ Thomson: Discovered that electrons could be
removed from atoms. Atoms could be broken up ­ making
Dalton's theory slightly wrong. Thomson suggested that atoms
were spheres of positive charge with tiny negative electrons stuck
in them like plums in a plum pudding.…read more

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Current Accepted Theory About The
Atomic Structure
· 1909 - Ernest Rutherford:
+
Fired alpha particles at thin
gold foil and found that:
Most went straight through. +
Majority of atom is space.
Alpha Source
+
A few were deflected.
There is a small dense
+
nucleus inside the atom.
A very small number
rebounded straight back. +
The nucleus has a positive
charge. +…read more

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Rutherford's Atomic Structure
The nucleus is tiny but makes up most of the
mass of the atom. It contains protons (which
Electrons
are positively charged) and neutrons (which
are neutral) ­ giving the charge overall as
positive.
The rest of the atom is mostly empty space.
The negative electrons move round the
outside of the nucleus really fast ­ giving the
+ atom its overall size.
Particle Mass Charge
Proton 1 +1
Neutron 1 0
Nucleus:
Electron ½000 -1
Protons + Neutrons…read more

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Nuclear Fission
When an atom with a very large nucleus absorbs a neutron:
·The nucleus splits into two smaller nuclei. A controlled
reaction is
·A large amount of energy is released. needed.
· The new atoms formed are themselves radioactive.
n
n
n n
n
=
n Explosion
n
· In the fusion process, further neutrons are released, which can cause
further nuclear fission resulting in a chain reaction.…read more

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The Nuclear Reactor
The chain reaction is controlled in a nuclear reactor. Large quantities of uranium can
be produced from a small amount of nuclear fuel. The products of the fission process
are radioactive, often with long half-lives, making the disposal of nuclear waste
difficult.
Control rods are raised and lowered to control the reaction and a moderator is used
to slow down the neutrons in an energy fuelled reactor.
Heat
Control Rods ­ absorb excess neutrons Exchanger
Concrete
Fuel Rods Steam
Hot
Enriched
Uranium
Water Coolant
Moderator Water
Casing…read more

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