ELECTRON THEORY
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• We will start our discussion of electron
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theory
with
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definitions.
• Matter- is anything that has mass and takes
up space.
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The basic unit of matter is the atom.
Another Definition
Energy- is the ability to do work.
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• There are two forms of Energy.
1. Heat Energy
2. Light Energy
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When we apply heat or light to an object
we are able to make it work for us.
As I said, the basic unit of matter is the Atom.
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The Atom is made up of:
The Nucleus- which is made up of
protons and neutrons
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Electrons- which revolve around the
nucleus in paths called
orbits or shells.
The Atom
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A substance that is made of atoms that are
all the same, is called an Element.
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A substance that is made up of two or
more different elements is called a
Compound.
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A substance that is the smallest particle of a
compound and still contains all the
characteristics of that compound is called a
Molecule.
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The Atom
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Electric Charges
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Electrons- have a negative charge.
Protons- have a positive charge.
Neutrons- have a no charge.
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An Electrically Neutral atom has the same
number of Protons and Electrons.
The number of Protons plus the number
of Neutrons is the Atomic Weight.
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The number of Protons is the
Atomic Number.
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The negatively charged ELECTRONS are held in
their orbits by their attraction to the positively
charged
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Electrons in the outermost shell are called
Valence Electrons.
Valence Electrons that leave
the outermost shell are called
Free Electrons.
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When an atom loses electrons it
becomes a positively charged Ion.
When an atom gains electrons it
becomes a negatively charged Ion.
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The process by which atoms gain or
lose electrons is called Ionization.
Some materials hold their electrons very
tightly. Electrons do not move through them
very well. These things are called Insulators.
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Plastic, cloth, glass and dry air are good
insulators.
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Other materials have some loosely held
electrons, which move through them very
easily. These are called Conductors. Most
metals are good conductors.
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Like aluminum, gold, silver and copper.
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The simplest form of electricity is
called Static Electricity.
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Cause of Static Electricity
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Static electricity is usually caused when
certain materials are rubbed against each
other, like wool on plastic or the soles of your
shoes on the carpet. The process causes
electrons to be pulled from the surface of one
material and relocated on the surface of the
other material.
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Rubbing a balloon on a wool sweater creates
charges on the surfaces. The material that
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loses electrons ends up with an excess of
positive (+) charges. The material that gains
electrons ends up an excess of negative (-)
charges on its surface.
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Charges on Surface
Note that the charged atoms are on the
surface of the material. Static electricity is
different than regular electricity that flows
through metal wires. Most of the time the
materials involved in static electricity are
nonconductors of electricity.
If electrical charges build up on the
outside of a metal, most of them will
dissipate into the metal, similar to an
electrical current.
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Rub a balloon on a wool sweater. The
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balloon
collects
negative
electrical
charges on its surface and the wool
collects positive charges. You can then
stick the balloon to the wall, which does
not have an excess of either charge. The
balloon will also stick to the wool,
although the charges may jump back to
the original material in a short time.
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You can also run a comb through
your
hair
to
charge
the
comb
with
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static electricity. The comb can then
be used to attract neutral pieces of
tissue.
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How a Battery Works
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A basic law of the universe is that like charges
repel and unlike attract.
Two
negatives
will
repel
each
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other.
A negative and a positive will attract each other.
An electron has a negative charge.
The negative terminal of a battery will push
negative electrons along a wire.
The positive terminal of a battery will attract
negative electrons along a wire.
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Electric current will therefore flow from the
negative terminal of a battery, through the lamp, to
the positive terminal.