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CBSE Class-12 Chemistry Quick Revision Notes
Chapter-01: The Solid State

• Solid:
Solid is a state of matter in which the constituting particles are arranged very closely
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• Properties of solids:
a) They have definite mass, volume and shape
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c) Intermolecular distances are short and hence the intermolecular forces are strong
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• Classification of on the basis of the arrangement of constituent particles:
a) Crystalline solids: The arrangement of constituent particles is a regular orderly
arrangement
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b) Amorphous solids: The arrangement of constituent particles is an irregular
arrangement
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• Properties of crystalline solids:
c) They have a definite characteristic geometrical shape
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e) They have a sharp melting point
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e
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g) They have a definite and characteristic heat of fusion
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i) When cut with a sharp edged tool, they split into two pieces and the newly generated
surfaces are plain and smooth
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• Polymorphic forms or polymorphs:
The different crystalline forms of a substance are known as polymorphic forms or
polymorphs
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• Characteristics of amorphous solids:
a) They have an irregular shape
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c) They gradually soften over a range of temperature
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e
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e) When cut with a sharp edged tool, they cut into two pieces with irregular surfaces
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g) They are called pseudo solids or super cooled liquids
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Types of crystalline solids:
Molecular Solids
A
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Constituent
Particles

Bonding/
Electrical
Attractive
conductivity
Forces
Dispersion or Insulator
London forces

Physical Melting Examples
nature
point
Soft

Very
low

Ar, CCl4,
H2,
I2,
CO2

Molecules

Dipole- dipole
interactions

Insulator

Soft

Low

HCl, solid
, solid NH3

Molecules

Hydrogen
bonding

Insulator

Hard

Low

H2O (ice)

Ionic Solids
Constituent Particles: Ions
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D
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• Lattice points or lattice sites:
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A group of lattice points which when repeated over and over again in 3
dimensions give the complete crystal lattice
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The crystal can consist of an infinite
number of unit cells
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b) Inclination of the edges to each other:
This is denoted by the angle between the edges α , β , and respectively
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• Seven crystal systems:
a) Cubic: α = β = γ = 90° , a = b = c
b) Tetragonal: α = β = γ = 90° ; a = b ≠ c
c) Orthorhombic: α = β = γ = 90°; a ≠ b ≠ c
d) Monoclinic: α = γ = 90°, β ≠ 90°; a ≠ b ≠ c
e) Hexagonal: α = β = 90°, γ =120°; a = b ≠ c
f)

Rhombohedral or trigonal: α = β = γ ≠ 90°; a = b = c

g) Triclinic: α ≠ β ≠ γ ≠ 90°; a ≠ b ≠ c
• Types of unit cells:
a) Primitive or simple unit cells have constituent particles only at its corners
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• Types of centred unit cells:
a) Face centred unit cell:
It consists of one constituent particle present at the centre of each face in addition to
those present at the corners
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It consists of a one constituent particle is present at its body centre in addition to
those present at the corners
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• Number of particles at different lattice positions:
a) Corner:
If an atom is present at any one corner, it is shared by eight unit cells
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b) Face centre:
If an atom is present at the centre of the face, it is shared by two unit cells
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c)

Body centre:
If an atom is present at the body centre, it is not shared by any other unit cell
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d) End centre:
If an atom is present at the edge centre, it is shared by four unit cells
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fourth of an atom belongs to the unit cell
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• Close packed structures:
a) Close packing in one dimension:
Each sphere is in contact with two of its neighbours
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b) Close packing in two dimensions: It is generated by stacking the rows of close packed
spheres in two ways:
i) Square close packing and ii) Hexagonal close packing
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It can be obtained in two ways:
i) Square close packed layers and ii) Hexagonal close packed layers
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This
way the spheres are aligned horizontally as well as vertically
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The coordination number is 4
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The arrangement is
ABAB type
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It has a AAAA type pattern
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• Three dimensional close packing from two dimensional hexagonal close packed layers: There
are two steps involved as:
i) Placing the second layer over the first layer
ii) Placing the third layer over the third layer
• Placing the second layer over the first layer:
If a two dimensional layer is considered as A, the second layer which is placed above the
first layer in such a way that the spheres of the second layer (considered as B) are placed
in the depressions of the first layer
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• Placing the third layer over the third layer:
There are two possibilities:
a) Covering the tetrahedral voids:
Here, tetrahedral voids of the second layer may be covered by the spheres of the third
layer
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The three dimensional structure is called
hexagonal close packed structure
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Examples: Mg, Zn
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b) Covering the octahedral voids:
Here, octahedral voids of the second layer may be covered by the spheres of the third
layer
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The three dimensional structure is
called cubic close packed structure or face centred cubic structure
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Example: Cu, Ag
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It is formed at the centre when four spheres are joined in the form of a tetrahedron
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•

•

•
•
•

In hexagonal close packing or cubic close packing arrangement, the octahedral and
tetrahedral voids are present
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The number of tetrahedral voids is twice the number
of octahedral voids
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4%
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414 times the radius of
the sphere
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414
R
Radius ratio for tetrahedral void:
For an atom to occupy a tetrahedral void, its radius must be 0
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r
= 0
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Relationship between radius of constituent particle (r) and edge length(a):
a) Simple cubic unit cell: a= 2r
b) Face centred unit cell: a  2 2r
4r
c) Body centred unit cell: a =
3

•

Volume of a unit cell = (edge length)3 = a3
a) Simple cubic unit cell: Volume= (2r)3

(

b) Face centred unit cell: Volume  2 2r

•

•
•
•

•

 4r 
c) Body centred unit cell: Volume = 

 3
Number of atoms in a unit cell (z):
a) Simple cubic unit cell: z = 1
b) Face centred unit cell: z = 4
c) Body centred unit cell: z = 2

)

3

3

Density of unit cell=
Crystal defects are basically irregularities in the arrangement of constituent particles
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b) Line defects
Line defects are the irregularities or deviations from ideal arrangement in entire
rows of lattice points
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c) Impurity defects
These are the defects in ionic solids due to the presence of impurities present in them
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This
defect results in decrease in density of the substance
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This defect results in increase in density of the
substance
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In this defect equal number of cations and anions are missing
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It decreases the density of a solid
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It includes NaCl,
KCl, CsCl and AgBr
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It creates a vacancy defect at its original site and an interstitial defect at
its new location
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Frenkel defect is shown by
ionic substance in which there is a large difference in the size of ions
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•

Different types of non-stoichiometric defects:
a) Metal excess
This type of defect is due to excess of metal cations
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b) Metal deficiency
This defect arises because of absence of metal ions from its lattice sites
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• Reasons for the cause of metal excess defect:
a) Anionic vacancies:
A compound may have an extra metal ion if the negative ion is absent from its lattice
site
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To maintain electrical neutrality this site is
occupied by an electron
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The F- centre is responsible for the colour of the compound
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An electron is present in the interstitial site to maintain the electrical neutrality
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b) Insulators
These are the solids with very low conductivities ranging between 10–20to10–10
ohm–1m–1
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•

•

Band theory
A metal is characterized by a band structure
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The gap between the
two bands is called forbidden band
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c) In case of semiconductors, forbidden gap is small
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Electrical conductivity of
semiconductors increases with rise in temperature, since more electrons can jump
to the conduction band
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Only some
electrons may jump to conduction band and show some conductivity
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Example: Silicon, germanium
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Their electrical conductivity is high
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The increase in conductivity is due to the negatively charged electrons
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The increase in conductivity is due to the positively charged holes
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Transistors:
They are made by sandwiching a layer of one type of semiconductor between two layers
of the other type of semiconductor
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The 12- 16 compounds:
These compounds are formed by the combination of group 12 and group 16 compounds
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Examples - ZnS, CdS, CdSe and HgTe
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They possess an average valency of 4
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Every substance has some magnetic properties associated with it
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Each electron in an atom behaves like a tiny magnet
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Classification of substances based on their magnetic properties:
a) Paramagnetic substances
These are those substances which are weakly attracted by the magnetic field
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b) Diamagnetic substances
Diamagnetic substances are weakly repelled by a magnetic field
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c) Ferromagnetic substances
These are those substances which are attracted very strongly by a magnetic field
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e) Ferrimagnetic substances
They have unequal number of parallel and antiparallel magnetic dipoles resulting in a
net dipole moment
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