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Semiconductors
Part
1: Atomic Structure
The Bohr Model
In the early
twentieth century, scientists began to uncover the secrets of the
atom. They found that the atom consisted of a nucleus, containing
neutrons and protons, around which orbit electrons. These high energy
particles are held together by the electrical attraction between
the positive protons and the negative electrons. This description
of the atomic structure is known as the Bohr model. Later research
showed that the protons, neutrons and electrons are in fact made
of up even smaller particles. For more information on quantum physics,
visit the web sites of these major research facilities: Fermi
National Accelerator Laboratory in the United States and CERN
in Switzerland. Releasing
the tremendous power locked in the atom can create nuclear energy
and atomic bombs. Knowledge of the atomic structure also enabled
researchers to develop the transistor.
Normally there
are an equal number of electrons and protons in every atom, and
the number of electron-proton pairs (the atomic number) determines
the physical and electrical properties of the element. If an electrical
force removes or adds electrons to the atom, it becomes a positive
ion (missing electron) or a negative ion (extra electron). The electrons
orbit the central nucleus at different energy levels known as orbital
rings or shells.
The diagram
shows the maximum number of electrons which may be located in each
shell of an atom. The outer shell, however, never contains more
than 8 electrons. Elements with 8 electrons in the outer shell (or
two, in the case of helium) are stable and do not interact chemically
with other elements. These are the inert gases. The atomic structure
also determines whether an element will be an electrical conductor,
and insulator, or a semiconductor.
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