electron theory electronology

ELECTRON THEORYLearning Objectives:At the end of the lesson the trainees should be able to:Define and differentiate the following:

Atom Element Molecule Compound

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Discuss Atomic structure of conductor, insulator and semiconductor

Discuss the significance of valence electrons. Explain ionization process. Explain and discuss different sources of Electricity

Introduction

Electricity is a fundamental entity of nature. It consists mainly of negatively and positively

charged particles commonly found in the atom.

Through man-made influence and natural phenomena, it is possible to observe how the electron (negatively charged) and the proton (positively charged) interact magnetically.

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The Theory

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Matter is anything that has weight and occupies space.

Examples of matter are air, water, automobiles, clothing, and even our own bodies.

Matter can be found in any one of three states: solid, liquid, and gaseous.

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• Any particle that is a chemical combination of two or more atoms is a molecule.

• In a compound, the molecule is the smallest particle that has all the characteristics of that compound.

MATTER MOLECULESMOLECULES

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• Water, for example, is a compound made up of two atoms of hydrogen and one atom of oxygen.

• It maybe chemically or electrically divided into its separate atoms, but it cannot be divided by physical means.

An atom is the smallest part into which an element can be divided.

Elements are the basic building blocks of all matter. Some common elements include silver, copper, gold, tin, hydrogen and oxygen

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MATTER MOLECULE ATOM

All atom consist of two basic parts: a body at the center of the atom, called Nucleus, and electron orbiting around the nucleus.

Atoms may have more than one orbiting electron, but each atom contains only one nucleus

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MATTER MOLECULE ATOM

Elements and Compounds• An element is a substance that cannot be reduced

to a simpler substance by chemical means. • Examples are iron, gold, silver, copper, and

oxygen. • All substances are composed of one or more of

these elements.• When two or more elements are chemically

combined, the resulting substance is a compound.

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Elements and Compounds• A compound is a chemical combination of

elements that can be separated by chemical but not by physical means.

• Examples of common compounds are water (hydrogen and oxygen) and table salt (sodium and chlorine).

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REMEMBEROne rule that is very prevalent in all forms of

electricity, and also magnetism, is that like charges, or poles, repel and unlike charges, poles, will attract.

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-- --

+ +

-- +

Composition of Atoms

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Atoms are composed of :Nucleus – at the center


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Atoms are composed of :Nucleus – at the center which consists of protons

(+) charge

++

PROTONS


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++

NEUTRONS


(+) charge and neutrons which has no charge.


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++

---- ELECTRONS


(+) charge and neutrons which has no charge. Electrons – orbiting the nucleus

Electron

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The electron is a fundamental sub-atomic particle which carries a negative electric charge

Within an atom the electrons surround the nucleus of protons and neutrons in an electron configuration.

In our study of electricity, we are particularly interested in the electrons in the outermost shell called ‘valence electron’.

The movement of valence electrons from one atom to another atom produces electric current .

Periodic Table of Elements

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For any element:Number of Protons = Atomic NumberNumber of Electrons = Number of Protons = Atomic NumberNumber of Neutrons = Mass Number - Atomic Number

Valence Electron

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These are the electrons in the outermost shell which are knocked or forced out to form a flow of electricity.

The maximum number of valence electrons is 8.

The larger the number of valence electrons, the tighter they are held in the atom, this is the property of an insulator.

Examples of insulators are plastic, rubber, wood, glass…

INSULATOR

Valence Electron

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A material that contain atoms with only 1 or 2 valence electrons is said to have unstable atoms these materials are conductors. Silver, copper, gold and aluminum all have one valence electron and are good conductors of electricity.

The flow of electricity is formed in these conductors when a stray electron bumps into the valence electron of an atom knocking it out of orbit.

CONDUCTOR

Valence Electron

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A material that is neither a conductor or an insulator is called a semiconductor.

A semiconductor will have 4 valence electrons and as they are heated they conduct more electricity.

The main semiconductor materials used are silicon and germanium.

A pure semiconductor material cannot be used to construct a device, so it is mixed or 'doped' with an impurity.

If water was absolutely pure, with no impurities, it would be an insulator.

SEMICONDUCTORSEMICONDUCTOR

Ionization The process by which an atom loses or gains electrons.

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Positive Ion

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Cu+29

--

--

• Positive ion is when an atom loses an electron.

• Example : Copper = 29 protons – 28 electrons = Cu+ ion

CLICK THE MOUSE ONCE TO IONIZE THIS COPPER ATOM.

--

--

----

--

--

--

-- --

--

--

----

--

--

--

--

------

--

--

--

--

--

----

Negative Ion

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Cu+ 29

--

--

--

--

--

--

--

----

-- --

-- --

--

--

--

----

----

-- ----

--

--

--

----

--

• Negative ion is when an atom gains an electron.

• Example : Copper = 29 protons – 30 electrons = Cu – ion

CLICK THE MOUSE ONCE TO IONIZE THIS COPPER ATOM.

--

Motion of electrons in a conductor

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--

--

-

--

--

-

--

-

-

-

-

-

-

- - - - - - -

- - - - - - -By applying energy to a conductor, the free electrons

will be pushed in a particular direction.

NO APPLIED FORCE

WITH APPLIED FORCE

(POTENTIAL DIFFERENCE)

- +

Electromotive Force Is the measure of push on each electron which makes the

electron move. Emf is the potential difference, or voltage, between the

terminals of a source of electricity. Electromotive force is usually measured in volts . The symbol for volts is V.

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eE

BE 6 V.

e

Voltage The term potential difference and voltage are often used

interchangeably to mean the “push”, thus you may see the term electromotive force (EMF)

When writing voltages in electrical formulas, the letter E is used to symbolize voltage or potential difference, while the letter V is more commonly used to abbreviate the unit of voltage on volts.

Potential difference always involve two points. If a potential difference exist between two points and a conductor is placed between them, current will flow.

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Sources of Electricity

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Chemical energy Voltage is produced by chemical reaction in a battery cell.

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Electromagnetism Voltage is produced in a conductor when the conductor

moves through a magnetic field, or a magnetic field moves through the conductor so that the magnetic lines of force of the field are cut.

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Light (photoelectricity) Voltage is produced by light striking photosensitive (light

sensitive) substances.

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Pressure (piezoelectricity) Voltage is produced by squeezing crystals of certain

substances.

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Pressure (piezoelectricity) Voltage is produced by squeezing crystals of certain

substances.

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Heat (thermoelectricity) Voltage is produced by heating the joint (junction) where two

unlike metals are joined.

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1.Battery - Direct Current – DC2.Generators - Alternating Current – AC 3.Solar Cell – Photovoltaic (PV) – DC4.Piezoelectric – DC5.Thermoelectric - DC

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VOLTAGE OUTPUTS OF SOURCES OF ELECTRICITY

Electron Current Flow

If a voltage exists across a complete conducting path, or a circuit, electrons flow in this circuit from low to high potential.

This flow of electrons is given the name “electron current”.

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Battery

-_ +

- - -

Conventional Current FlowIt is the reverse of “electron flow”. It is the flow of positive charges from high to low

potential.

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Battery

+_ +

+++

Current

It is the movement of electrons in a particular direction as pushed by an electromotive force.

Movement of electrons = Current The symbol for current is “ I “The strength of current is measured in Amperes

represented by A or Amps.A current flowing in a single direction is called a

direct current (d.c.)When the direction of flow of current is continually

reversing, it is called an alternating current (a.c.)

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Closed or Complete Circuit

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Current can only flow in a closed circuit

Direct Current

Is a steady current flowing in a single direction

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Battery

e_ +

e e e

Direct Current (DC) Voltage

The DC voltage means that the polarity of the voltage never changes, the positive terminal always has positive voltage and the negative terminal always has negative voltage.

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Output of the positive battery terminal with respect to its negative terminal

Alternating CurrentIs when the direction of flow of current is continually

reversing

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A.C. Generator

eeee

Alternating Current (AC) Voltage Alternating current (AC) is current derived from a voltage

which is continuously varying. The mains voltage being fed to our house is 220 volts AC. The voltage is derived from a generator at the power station

which is basically a coil of wire being rotated within a large magnet, this action causes the lines of flux in the magnet to be cut, inducing a voltage into the coil of wire.

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In modern ships the main supply is usually A.C. but D.C. has many uses.

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Summary

• Matter is anything that has weight and takes up space.• All matter is made up of molecules.• All Molecules are made up of Atoms.• Atoms are made up of Protons and Neutrons in a nucleus with

electrons forming shells around them – much like the solar system.

• Electrons have a negative charge, Protons have a positive charge, and Neutron has no charge.

• Electrons can be forced to move from one atom to the next and this is accomplished using electromotive force.

• This movement of electrons is electrical current.

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PROPERTIES OF CRYSTAL• Some substances, when in solid state, will have a molecular

structure termed crystalline• A crystalline structure is one in which the atoms or

molecules take up precise positions in a geometric form of lattice

• The structure of a solid substances which do not have a symmetric arrangement of their atoms or molecules is termed amorphous

• Some crystalline substances the imperfections in the molecular structure will confer additional properties on the materials, such as luminescence, chemical effects or electrical effects

• Crystals of substances which exhibit electrical properties due to imperfections in their molecular structure are termed semiconductor

• Examples of semiconductors are:

• Germanium, Silicon• One important electrical

property of all semiconductors such as Ge & Si is that a reduction in resistance with increase in temperature are said to have a negative temperature coefficient.

Covalent bond- Bonding in which atoms share electrons

• Under normal conditions, semiconductors cannot be classified as conductors or insulators.

• A semiconductor crystal is at some temperature above absolute zero there will be:

some level of internal energy due to the normal molecular motion (vibrations) within the crystal lattice structure.

a number of free electrons in the crystal lattice moving randomly through it and acting as charge carrier

Characteristics of a semiconductor materials

• Under certain imposed conditions semiconductors can behave as conductors or insulators

• At the absolute zero of temperature (0 K or -273 oC) all particles forming the semiconductor crystal will at rest and will occupy precise positions in a geometric lattice structure, and that:

the internal energy (due to molecular motion) will be zero

there will be no free electrons to act as charge carriers

it behave as perfect insulator

Characteristics of a semiconductor materials

• 1. How much energy in Joules is required to move a charge of 6 coulomb through a difference in potential of 3 Volts?

• 2. How many Joules does a 40-watt light bulb consume in 1 Day?

• 3. Find the current flow through a light bulb from a steady movement of

a. 60 C in 4 sec.b. 15 C in 2 min.

• 4. Find the average input power to a radio that consumes 3600 J in 2 min. (from rearranging P=W/t and from the fact that 1 Ws=1J.)

• 5 Find the conversion relation between kilowatt-hours and joules. (The approach here is to convert from kilowatt-

hours to watt-seconds, and then use the fact that 1J = 1 Ws)• 6. If 48eV of energy is required to moved a charge through a

potential difference of 12Volts, determine the charge involved. (1eV= 1.6x10-19 J)

• Problems-Calculation

electron theory electronology

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