The document discusses atomic structure, including Niels Bohr's theory which describes the behavior of electrons around the nucleus. It also classifies solids based on their electrons and energy bands, differentiating between conductors, insulators, and semiconductors. Additionally, it covers the properties of semiconductors, their types, and the effect of temperature on their conductivity.

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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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