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.
4
Conductor/Insulator/Semiconductor
• Elements whose electrons are stable and
cannot easily move from one atom to
another make good insulators.
• Any elements that are not considered
conductors or insulators are categorized as
semiconductors.
5
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.
6
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.
7
Conductors: Example Ag & Cu
Silver
(Ag)
2
8
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.
Copper
(Cu)
1
18
8
2
This free flow of
electrons is what makes
silver and copper good
conductors.
Nucleus
Number of
Electrons in Orbit
8
Insulator
• When an element’s outer ring is complete,
or full, its electrons cannot 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.
9
Insulator
• Plastics are polymers or long chains of
atoms bonded to one another.
• Neon and argon, both gases, are good
insulators and are often used in light
bulbs.
10
Insulator: Example Ne & Ar
Neon
(Ne)
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.
This stable electron
structure is what makes
neon and argon good
insulators.
Argon
(Ar)
8
8
2
11
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:
Carbon (used to make resistors).
Silicon (used to make transistors)
12
Semiconductors: Example C & Si
Carbon
(C)
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.
This electron structure is
what makes carbon and
silicon good
semiconductors.
Silicon
(Si)
4
8
2
13