Basic Electron Theory
Digital Electronics
Basic Electron Theory
This presentation will
• Review the basic structure of the atom.
• Define conductor, insulator, and semiconductor.
2
Structure of an Atom
Example – Carbon Atom
Nucleus
• 6 Protons
• 6 Neutrons
-
-
Electrons
-
+ +
-
Orbits
-
-
The distribution of electrons in the orbital rings around an
atom’s nucleus determines the element’s electrical properties.
3
Conductor / Insulator / Semiconductor
• The stability of the electrons in the outer ring determines
whether a material made from this element is a
conductor, insulator, or semiconductor.
• Elements whose electrons are unstable and can easily
move from one atom to another make good conductors.
• Elements whose electrons are stable and can not easily
move from one atom to another make good insulators.
• Any elements that are not considered conductors or
insulators are categorized as semiconductors.
4
Conductors
• When an element’s outer electron ring is incomplete or not
full, its electrons can move more freely from one atom to
another atom.
• Elements whose electrons can move more freely make
good conductors.
• In general, most metals make good conductors because
they only have one or two electrons in their outer band.
• Silver and gold are the best conductors. Copper is the
second best conductor. Most wiring uses copper wire
because it is a good conductor and is less expensive than
the other metals.
5
Conductors: Example Ag & Cu
2
8
Silver
Copper
(Ag)
(Cu)
18
18
1
Because the outer-most
band is incomplete, the
single electron is unstable
and loosely bonded to the
atom. Hence, it can easily
move to the outer band of
another adjacent atom.
1
18
8
2
This free flow of electrons
is what makes silver and
copper good conductors.
Nucleus
Number of
Electrons in Orbit
6
Insulator
• When an element’s outer ring is complete, or full, its
electrons can not easily move from one atom to another
atom.
• Elements whose electrons can not move freely make
good insulators.
• Examples of good insulators are glass, plastic, rubber,
paper, or air. Most wiring uses plastic as an insulator.
• Plastics are polymers or long chains of atoms bonded to
one another. Viewing the atomic structure of plastics is
far beyond the scope of this class (If you are interested
in such topics, you may want to take AP Chemistry.).
• Neon and argon, both gases, are good insulators and
are often used in light bulbs.
7
Insulator: Example Ne & Ar
Neon
Argon
(Ne)
(Ar)
2
8
The outer-most orbits of neon and
argon can each contain a maximum
of eight (8) electrons. This is exactly
how many they have. This makes
the electron in the outer-most
bands stable.
8
8
2
This stable electron structure is
what makes neon and argon good
insulators.
8
Semiconductor
• When an element’s outer ring is neither
complete nor incomplete, the element is
considered to be a semiconductor.
• Examples of good semiconductor materials are
– Carbon (used to make resistors)
– Silicon (used to make transistors)
9
Semiconductors: Example C & Si
Carbon
Silicon
(C)
(Si)
2
4
The outer-most orbits of carbon and
silicon can each contain a
maximum of eight (8) electrons.
Because they both contain four (4),
these electrons are neither stable
nor unstable.
4
8
2
This electron structure is what
makes carbon and silicon good
semiconductors.
10