This presentation gives you idea about following topics 1.atomic structure 2.classification of solids based valance electron, free electron, energy band description 3.semiconductor and its type

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DELIBERATION OF
TOPICS:
Atomic structure
Classification of solids
Semiconductor

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Atomic Structure:
1.1 Neils bhor theory:
Atom consists of
+ve charge  nucleus, -ve  electrons (revolve in circular
orbits).
Electron revolve around nucleus only in certain permitted orbits.
Each orbit certain fixed amount of energy.
Additional energy of electron excitation.
orbit name K,L,M,P…
Nucleus protons + neutrons.
Protons (positively charge), neutrons(neutral)
Atomic weight = no of protons + no of neutrons.
Atomic number = no of protons / no of electrons in atom
No of electrons in orbit2n2

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1.2. Structure of elements:
No of electrons in any orbit2n^2 nnumber of orbits
Example:
1st
 2 electrons
2nd
 8 electrons
3rd
 18 electrons
Atomic structure: ex copper
Atomic weight = 64
Atomic number =29
No of protons = no of electrons = 29
No of neutrons = 64-29 = 35
Electron29 1st
orbit2, 2nd
orbit8, 3rd
orbit18, 4th
orbit 1

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1.3 Electron:
tiny particles electrons
Negatively charged particle have negligible mass
Important properties:
Charge of electrons, e = 1.602 *10^-19 coulomb
Mass of electrons, m = 9.0*10^ -31kg
Radius of an electron, r = 1.9 * 10^-15meter
Ratio e/m of electron is 1.77*10^11coulombs/kg
mass of an electron is very small
very mobile and greatly influenced by electric or magnetic
fields
Energy of an electron:
2 types kinetic energy due to its motion
Potential energy due to charge on the nucleus
Total energy = K.E+P.E
Energy of electron increases as its distance from the nucleus
increases.
Last orbits electron possess very high energy as compared to electron
in the inner orbits.

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1.4 Energy band:
range of energy possessed by an electron in
a solid is known as energy bands
Each orbit of an atom has a single energy

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1.5 Energy band description:
Bands are classified into 2 types :
1.Valence band:
energy possessed by valence electron.
2.Conduction band:
energy possessed by free electron.
3.Forbidden energy gap:
separation between conduction band and
valance band on the energy level diagram.
width measures the bondage of valence
electrons to the atom.

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Classification of solids:
2.1.classification based on:
1.valance electrons
2.Free electrons
3.Forbidden energy gap
Valance electron:
determines the metal, non-metal, solids, gas, and electrical
properties of a material.
based on outermost valance electron.
Electrical conductivity of material are classified into
conductor
insulator
semi-conductor
Conductor:
valance electron < 4
Insulator:
valance electron > 4
Semi-conductor:
valance electron = 4

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Examples:
1.Conductor:
2.Insulator:

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3.semi-conductor:

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Free electrons:
valance electrons which are Loosely attached to the
nucleus
Conductor:
has large number of free electrons
Insulator:
has no free electrons
Semi-conductor:
has few free electrons

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Forbidden energy gap:
1.Insulator:
do not allow the passage of electric current
2.conductor:
which easily allow the passage of
electric current.

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3.Semi-conductor:
electrical conductivity lies in-
between conductor and insulator.
negative temperature co-
efficient of resistance.

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Why silicon is widely used as
semiconductor?
Answer is…….

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germanium valence electron  Higher energy level

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Semi-conductor:
Substance which has resistivity (10^-4 to 0.5ohmmeter)
3.1. properties of semiconductor:
(a). Resistivity of a semiconductor less than insulator but
more than conductor.
(b). consists of negative temperature co-efficient of
resistance
(c). By adding impurity current conducting properties
change appreciably

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3.2. Bonds in semiconductor:
Semi-conductor bonds  covalent bonds

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3.3. Effect of temperature on semiconductor:
(i).At absolute zero:
 act as perfect insulator
(ii).Above absolute zero:
 act as perfect conductor

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3.4.Hole current:
The current conduction by holes.
1. Due to movement of
valence electron from
one covalent bond to
another.
2. Current flow due to
presence of holes in
covalent bond

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3.4.Types of semi-conductor:
semi-conductor is classified as two type
(i).Intrinsic semi-conductor
(ii).Extrinsic semi-conductor
(i).Intrinsic semi-conductor:
extremely pure form of semiconductor

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(i).Extrinsic semi-conductor:
impure form of semiconductor
Doping:
adding impurity to the semiconductor
Two types of impurity:
1.Pentavalent impurity (donor impurity)
2.Trivalent impurity (acceptor impurity)
Pentavalent impurity  n-type semiconductor
Trivalent impurity  p- type semiconductor
N-type semiconductor:

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N-type conductivity:
current conduction predominantly by free electron

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P-type semi-conductor:
current conduction predominantly by holes

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P-type conductivity:
current conduction predominantly by holes

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Summarization of topics discussed:
1.Atomic structure
2. classification of solids
3.Semiconductors

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