Thomson:
§Thomson's atomic model is a theory of
atomic structure proposed in 1904 by Joseph John Thomson, who discovered the
electrón1 in 1897, long before the discovery of the proton and the neutron. In
this model, the atom is composed of negatively charged electrons in an atom
positive pasas.2 as pudding was thought that the electrons are distributed
uniformly around the atom. At other times, instead of a cloud of negative
charge was running with a cloud of positive charge.
Rutherford:
§In 1909 Ernest Rutherford
conducted what is now a famous experiment where he bombarded gold foil with
alpha particles (Helium nuclei). A source which undergoes alpha decay is
placed in a lead box with a small hole in it. Any of the alpha particles
which hit the inside of the box are simply stopped by the box. Only those
which pass through the opening are allowed to escape, and they follow a
straight line to the gold foil. The animation below shows the experiment in action.
Bohr:
§Bohr used these observations to
argue that the energy of a bound electron is "quantized."
Quantized is a fancy word meaning only certain quantities of energy are
allowed. This explanation addresses the true origin
of light. Since only certain
energy levels are allowed it is actually possible to diagram the atom in terms
of its energy levels. In the animation below you will see a model of a
Hydrogen atom and to the right of it, a Bohr energy level diagram.
Cloud:
§The cloud model represents a
sort of history of where the electron has probably been and where it is likely
to be going. The red dot in the middle represents the nucleus while the
red dot around the outside represents an instance of the electron.
Imagine, as the electron moves it leaves a trace of where it was. This
collection of traces quickly begins to resemble a cloud. The probable
locations of the electron predicted by Schrödinger's equation happen to
coincide with the locations specified in Bohr's model.
reference:
by: andres, correa
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