Slides in this set
Previous Theories About The
· 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
· 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
Current Accepted Theory About The
· 1909 - Ernest Rutherford:
Fired alpha particles at thin
gold foil and found that:
Most went straight through. +
Majority of atom is space.
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
Rutherford's Atomic Structure
The nucleus is tiny but makes up most of the
mass of the atom. It contains protons (which
are positively charged) and neutrons (which
are neutral) giving the charge overall as
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
Electron ½000 -1
Protons + Neutrons…read more
When an atom with a very large nucleus absorbs a neutron:
·The nucleus splits into two smaller nuclei. A controlled
·A large amount of energy is released. needed.
· The new atoms formed are themselves radioactive.
· In the fusion process, further neutrons are released, which can cause
further nuclear fission resulting in a chain reaction.…read more
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
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.
Control Rods absorb excess neutrons Exchanger
Fuel Rods Steam