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History of Atomic Model
• Democritus:
• - all things are composed of minute, invisible,
and indivisible particles, atoma (indivisibles) in
constant motion through otherwise empty space.
• Sir Joseph John Thompson 1900:
• analyzed the nature of cathode rays
• he reduced that they had particles like
properties and were identical regardless of the
material producing the rays.
• Plum-Pudding Model:
• - Lord Kelvin and JJ Thompson concluded that
the atom was composed of tiny negatively
charged electrons and positive charge mixed
together. This was called the Plum-Pudding
• Rutherford Gold Foil Experiment 1911:
• - Ernst Rutherford shot alpha particle at
extremely thin gold foil
• - This result was thought to be like cannon balls
bouncing off
• - Most went right through with little deflection,
but some bounced back tissue paper
• Rutherford Atomic Model:
• -The alpha particle must have bounced off an
area of the atom that is positively charged and
extremely dense
• -Rutherford concluded that the atom has a dense
positive nucleus with electrons orbiting around.
• Bohr Model 1913
• - Light is emitted from matter at particular
energies, or quanta
• -Light is produced when electrons moved from
high energy atoms to low energy atoms
• - Electrons exist at particular orbits
• Modern Atomic Model:
• - Quantum Mechanism shows how there is a
limit to our ability to determine the motion and
position of particles
• - The motion of objects is described using a
wave equation Ψ (PSI), where Ψ is the
probability distribution around the hydrogen
atom we obtain orbital shapes.
• Inside the Nucleus
• - the nucleus contains protons and neutrons
• - protons and neutrons are composed of quarks
• -the strong force between the quarks is what
holds the nucleus together. The mechanism is
still not well understood.