Compendium ClassXIIChemistry
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Transcript of Compendium ClassXIIChemistry
Compendium/Chemistry/Class XII 1 © 2010 Vidyamandir Classes
Dear Students,Vidyamandir Classes academic team knows that you are rigourously studying to cover the entire prescribedsyllabus. As the Final Exams approach, this is the time when you need to revisit the concepts you havelearned. At this time, you have to be very focused and directed in your approach.To make your learning process precise, effective and enjoyable, we at Vidyamandir Classes conceptualizedthe compendium series, strategically designed to help you in scoring high grades in examination. TheCompendium is primarily intended to present the concepts of chapter in a concise manner. All key definitions,diagrams and formulae have been integrated for a quick revision of the chapter.To help you to easily master complicated concepts, definitions, diagrams and formulae, we have addedinteresting tips, mnemonics, maps and matrices. Let us take a look at the elements of the Compendium andhow to use them.Knowing these features will make it easier for you to assimilate complex information.
Icon Description How it can help you
Concept map To directly recapitulate main concepts of the
chapter.
Drawing Tips
Drawing Tips
To help you draw and remember diagrams, we have thoughtfully developed some mnemonics to help you to memorise information
Compare Contrast Matrix To help you in comparing different concepts
Memory Tips To make your learning process effective, easy
tips have been provided.
In this compendium, we have also incorporated:• CBSE Blue Print: Type of questions asked and the weightage of different forms of questions.• Analysis of Previous Years CBSE questions: The topic wise analysis of previous years question along
with the marks allocated.• We are confident that this Compendium will prove very helpful in achieving excellent result in your
exams.
All the very best for your exams!Vidyamandir Classes Academic Team
ABOUT THE COMPENDIUM
Compendium/Chemistry/Class XII 2 © 2010 Vidyamandir Classes
The Solid State
Matter exists in nature in four states namely solid, liquid, gas and plasma. All these statesdiffer from each other in attractive forces, and arrangement of particles. This chapter looks atsolid state in detail.
Solids are of two types as given in the following table with their properties:
About The Solid State
Property Crystalline Solids Amorphous Solids
1. Shape Have definite characteristic geometrical shape
Irregular shape
2. Melting point
Have sharp and characteristic temperature
Soften over a range of temperature
3. Cleavage property
On cutting with a sharp edge tool, these cut into two pieces having smooth surfaces and plain
On cutting with a sharp edge tool, these cut into two pieces with irregular surfaces
4. Anisotropy Isotropic in nature Anisotropic in nature
5. Nature True solids Pseudo solids or supercooled liquids
6. Order in arrangement of constituent particles
Long range order Short range order
Compendium/Chemistry/Class XII 3 © 2010 Vidyamandir Classes
Molecular solids Type of solid Non polar Polar Hydrogen
bonded
Ionic solids Metallic solids
Covalent or network solids
Examples Ar, CCl4 HCl, SO2, HBr
H2O (ice)
NaCl, CsCl, MgO, ZnS, CaF2
Fe, Cu, Ag, Mg
SiO2 (quartz), SiC, C (diamond), AlN, C(graphite)
Constituent particles
Molecules Molecules Molecules Ions Positive ions in sea of delocalized
Atoms
Bonding forces Weak dispersion forces
Dipole-dipole interaction
Hydrogen bonds
Coulombic Metallic bonding
Covalent bonding
Physical nature Soft Soft Hard Hard but brittle
Hard but malleable and ductile
Hard, graphite is soft
Melting point Very low Low Low High Fairly high Very high Electrical conductivity
Insulator Insulator Insulator Insulator in solid state but conductors in molten state or aqueous solutions
Conductors Insulators Graphite (exception) is conductor
Crystalline solids can be further classified into four categories.
Crystal LatticesThe constituent particles (atoms, ions or molecules) of a crystal are arranged in a definite andregular order in space. The relative positions of such particles in a crystal are shown by points.The arrangement of these points in a crystal is called space lattice. The seven crystal systemsform the 14 possible Bravais lattices listed in the following table:
Crystal System Types of Lattices
Cubic Simple, Face centred, Body centred
Tetragonal Simple, Body centred
Orthorhombic Simple, Face centred, Body centred, End Centred
Monoclinic Simple, End Centred
Rhombohedra Simple
Triclinic Simple
Hexagonal Simple
Compendium/Chemistry/Class XII 4 © 2010 Vidyamandir Classes
The seven crystal systems form the following Bravais lattices according to the arrangement ofthe points in the different unit cells involved.
Figures of 14 Bravais lattices associated with the seven crystal systems are:
Crystal system Possible variation
Axial distances or edge lengths
Axial angles Examples
Cubic
Primitive, Body-centred, Face-centred
a = b = c
α = β = γ = 90°
NaCl, KCl, Diamond, Zinc blende (ZnS), Cu, Ag
Tetragonal
Primitive, Body-centred
a = b c
α = β = γ = 90°
White tin, SnO2, TiO2, CaSO4
Orthorhombic
Primitive, Body-centred, Face-centred, End-centered
a b c
α = β = γ = 90°
Rhombic sulphur, KNO3, K2SO4, BaSO4, PbCO3
Hexagonal Primitive a = b c α = β = 90°, γ = 120° Graphite, ZnO, CdS, PbI2
Rhombohedral or Trigonal
Primitive a = b = c α = β = γ 90° Calcite (CaCO3), quartz NaNO3, HgS (Cinnabar)
Monoclinic
Primitive, End-centered
a b c
α = γ = 90°, β 120°,
Monoclinic sulphur, Na2SO4 .10H2O
Triclinic Primitive a b c α β γ 90° CuSO4.5H2O, K2Cr2O7, H3BO3
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CENTRED UNIT CELLS
Atoms are present at eight corners(one atom shared between eightcubes) and one (not shared withany) atom is present at the centreof the cube.
Atoms are present at eight corners(one atom shared between eightcubes) and six atoms (each sharedbetween two cubes) present on thesix faces of the cube.
Body-centred unit cell
No. of atoms in unit cell1 8+1 28
Face-centred unit cell
No. of atoms in unit cell 1 1= 8+6 48 2
End-centred unit cells
CLOSE PACKED STRUCTURESIn solids the constituent particles are close-packed, leaving minimum vacant space. Closepackings are of following types:(i) Close Packing in One Dimension: the spheres representing particles touch each other in a
row, the coordination number is 2.
(ii) Close Packing in Two Dimensions:Square close packing: Can be generated by placing together the rows of close packedspheres (Arrangement 1).Hexagonal close packing: Generated by placing the second row on the depression betweenthe spheres of first row (Arrangement II).
Compendium/Chemistry/Class XII 7 © 2010 Vidyamandir Classes
Voids: The empty spacesbetween atoms in a crystal arecalled voids. Voids are of threetypes: tetrahedral, octahedraland trigonal voids.
(iii) Close Packing in Three Dimensions:
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IMPERFECTIONS IN SOLIDS: CRYSTAL DEFECTS
Types of Defects Diagram Examples
Vacancy defect
Some lattices are vacant
Point defects
Stoichiometric defects
Interstitial defect
Constituent particles occupy an interstitial site
Calculations involving unit celldimensions
Density of anunitcellMassof unitcell
Volumeof unit cellzMor d 3a NA
where, z = number of atoms inunit cell
M = Molar massNA = Avogadro constanta3 = Volume of unit cell
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Frenkel defect, also called dislocation defect
A vacancy defect at original site and interstitial defect at new location,
ZnS, AgCl, AgBr, AgI
Stoichiometric defects
Schottky defect
This defect has equal number of cations and anions
NaCL, CsCl, KCl, AgBr
Impurity defects Impurity occupies the sites of a crystal
SrCl2 in NaCl, solid solution of CdCl2 and AgCl
Metal excess defect
Due to the presence of extra cations at interstitial sites
ZnO
Point defects
Non stoichiometric defects
Metal deficiency defect
Have less amount of metal compared to stoichiometric proportion
FeO which is mostly found with a composition of Fe0.95O
Compendium/Chemistry/Class XII 10 © 2010 Vidyamandir Classes
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ANALYSIS OF CBSE QUESTIONS (2004-08)
CONCEPTS YEAR(S)
Crystal structure, formula of compound Close packed structures Defects in crystals Semiconductors Magnetic properties Numerical on unit cell dimensions
2008, 2006, 2005 2007 2007, 2006, 2004 2007 2007 2008, 2007, 2006, 2005, 2004
CBSE BLUEPRINT
Types of questions Very short answer (1 mark)
Short answer I (2 marks)
Short answer II (3 marks)
Total marks
Option I 1 – 1 1 + 3 = 4
Option II – 2 – 2 2 = 4
Tips to answer
Formula of a compound Check the type of lattice (ccp, hcp, etc.), find the number of voids and occupancy of the elements of the compound in lattice and voids. Find the ratio of two, e.g., A:B = 4:3 gives the formula A4B3
Coordination number Find the type of packing, then the number of closest neighbours
Doping Indicate the type of element with which silicon, germanium are to be doped, e.g. group 15 element gives n-type (electron rich) whereas group 13 element gives p-type (electron deficient) semiconductors
Number of atoms in unit cell Check that how many atoms are shared between the unit cells in vicinity and calculate accordingly
Atomic radius, density, number of atoms etc.
Can be calculated using formula
3A
Z×MDensity of the unitcell = a N
Number of tetrahedral voids Twice the number of atoms
Number of octahedral voids Number of atoms
Number of vacancies on adding ions
Number of corresponding ions added