Using gas discharge tubes, William Crookes 18321919 noticed that with an electric current corpuscles

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Probing the Atom
Using gas discharge tubes, William Crookes
(1832-1919) noticed that with an electric current
(corpuscles) from a Cathode a pinwheel would
rotate.
These corpuscles were shown to have a negative
charge by John Thompson in (1856-1940). He
called them electrons.
Eugen Goldstein did the same experiments with
Anodes and discovered the proton.
Led to the Thompsons RAISIN BUN MODEL
Electrons are embedded in a positive dough
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Radiation

• Beta Particles (-)
• Fast moving electrons

• Gamma Rays
• Energy wave

• Alpha Particles ()
• 4x the mass of a proton

Rutherford used radiation and his gold foil
experiment to postulate that atoms must contain
A Nucleus - a very positive, dense and
massive core
An Electron Cloud - a low density, negative
envelope around the
nucleus
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Scientists didnt believe Rutherford
Wouldnt negative electrons spiral into the
positive nucleus?

• Niels Bohr (1885-1962) added further proof to
  Rutherfords model

• Atoms are like a solar system

• Planets - Electrons

• Sun - Nucleus

Orbits - Electron Shells
Shells are 3 dimensional and sphere like - the
shell in which electrons reside depends on the
amount of energy electrons possess
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We have heard about Protons and Electrons but
there is one more particle
Neutrons
Neutrons are about the same mass as Protons are
are located in the nucleus.
They sit between protons so the repulsive
positive forces between the atoms are not so
great that the nucleus splits
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Isotopes When one extra neutron is added to or
removed from the element..