Class – XII
Subject – Chemistry
SOLID STATE
ASSIGNMENT
NCERT
Example
1.1 A compound is formed by two
elements X and Y. Atoms of the element Y (as anions) make ccp
and those of the element X (as cations) occupy all the octahedral voids.
What is the formula of the compound?
Ans:-XY
1.2 Atoms of element B form hcp
lattice and those of the element A occupy 2/3rd of tetrahedral voids.
What is the formula of the compound formed
by the elements A and B?
1.3 An element has a body-centred
cubic (bcc) structure with a cell edge of
288 pm. The density of the element is 7.2 g/cm3. How
many atoms are present in 208 g of
the element?
Ans:-24.16×1023 atoms
1.4 X-ray diffraction studies
show that copper crystallises in an fcc
unit cell with cell edge of 3.608×10-8 cm. In a separate
experiment, copper is determined to have a density of 8.92 g/cm3, calculate the atomic mass of copper. Ans:-63.1u
1.5 Silver forms ccp lattice and X-ray studies of its crystals show that the edge length of its unit cell
is 408.6 pm. Calculate the density of silver (Atomic mass = 107.9 u). Ans:-10.5×103 kg m-3
Intext
Questions
1.1 Why are solids rigid?
1.2 Why do solids have a definite
volume?
1.3 Classify the following as
amorphous or crystalline solids: Polyurethane, naphthalene, benzoic acid,
teflon, potassium nitrate, cellophane, polyvinyl chloride, fibre glass, copper.
1.4 Why is glass considered a
super cooled liquid?
1.5 Refractive index of a solid
is observed to have the same value along all directions. Comment on the nature
of this solid. Would it show cleavage property?
1.6 Classify the following solids
in different categories based on the nature of intermolecular forces operating
in them:
Potassium sulphate, tin, benzene, urea, ammonia, water, zinc
sulphide, graphite, rubidium, argon, silicon carbide.
1.7 Solid A is a very hard
electrical insulator in solid as well as in molten state and melts at extremely
high temperature. What type of solid is it?
1.8 Ionic solids conduct
electricity in molten state but not in solid state. Explain.
1.9 What
type of solids are electrical conductors, malleable and ductile?
1.10 Give
the significance of a ‘lattice point’.
1.11 Name the parameters that
characterise a unit cell.
1.12 Distinguish between:-
(i) Hexagonal and monoclinic unit cells
(ii) Face-centred and end-centred unit cells.
1.13 Explain how much portion of
an atom located at (i) corner and (ii) body centre of a cubic unit cell is part
of its neighboring unit cell.
1.14 What is the two dimensional
coordination number of a molecule in Square
close-packed layer?
Ans- 4
1.15 A compound forms hexagonal close-packed structure.
What is the total number of voids in 0.5 mol of it? How many of these are
tetrahedral voids?
Ans- Total number of voids = 9.033 × 1023
Number of tetrahedral voids = 6.022 × 1023
1.16 A compound is formed by two
elements M and N. The element N Forms ccp
and atoms of M occupy 1/3rd of tetrahedral voids.
What is the formula of the compound?
Ans-M2N3
1.17 Which of the following
lattices has the highest packing efficiency (i) simple cubic (ii) body-centred
cubic and (iii) hexagonal close-packed lattice?
1.18 An element with molar mass
2.7×10-2 kg mol-1 forms a cubic unit cell with edge
length 405 pm. If its density is 2.7×103 kg-3, what is the nature
of the cubic unit cell? Ans- ccp
1.19 What type of defect can arise
when a solid is heated? Which physical
property is affected by it and in what way?
1.20 What type of stoichiometric
defect is shown by:
(i) ZnS (ii) AgBr
1.21 Explain how vacancies are
introduced in an ionic solid when a cation of higher valence is added as an
impurity in it.
1.22 Ionic solids, which have
anionic vacancies due to metal excess defect, develop colour. Explain with the
help of a suitable example.
1.23 A group 14 element is to be
converted into n-type semiconductor by doping it with a suitable impurity. To
which group should this impurity belong?
1.24 What type of substances would
make better permanent magnets, ferromagnetic or ferrimagnetic. Justify your
answer.
EXERCISE
QUESTION
1.1 Define the term 'amorphous'.
Give a few examples of amorphous solids.
1.2 What makes a glass different
from a solid such as quartz? Under what conditions could quartz be converted
into glass?
1.3 Classify each of the
following solids as ionic, metallic, molecular, network (covalent) or
amorphous.
(i) Tetra phosphorus decoxide (P4O10)
(vii) Graphite
(ii) Ammonium phosphate (NH4)3PO4
(viii) Brass
(iii) SiC
(ix) Rb
(iv) I2
(x) LiBr
(v) P4 (xi) Si
(vi) Plastic
1.4 (i) What is meant by the term
'coordination number'?
(ii) What is the coordination number of atoms:
(a) in a cubic close-packed structure?
(b) in a body-centred cubic structure?
1.5 How can you determine the
atomic mass of an unknown metal if you know its density and the dimension of
its unit cell? Explain.
1.6 'Stability of a crystal is
reflected in the magnitude of its melting points'.Comment. Collect melting
points of solid water, ethyl alcohol, diethyl ether and methane from a data
book. What can you say about the intermolecular forces between these molecules?
1.7 How will you distinguish
between the following pairs of terms:
(i) Hexagonal close-packing and cubic close-packing?
(ii) Crystal lattice and unit cell?
(iii) Tetrahedral void and octahedral void?
1.8 How many lattice points are
there in one unit cell of each of the following lattice?
(i) Face-centred cubic
(ii) Face-centred tetragonal
(iii) Body-centred
1.9 Explain:-
(i) The basis of similarities and differences between metallic
and ionic crystals.
(ii) Ionic solids are hard and brittle.
1.10 Calculate the efficiency of
packing in case of a metal crystal for
(i) simple cubic
(ii) body-centred cubic
(iii) face-centred cubic (with the assumptions that atoms are
touching each other).
1.11 Silver crystallises in fcc
lattice. If edge length of the cell is 4.07 × 10–8cm and density is
10.5 g cm–3, calculate the atomic mass of silver.
[Ans.: 103u]
1.12 A cubic solid is made of two elements P and Q. Atoms of Q are at
the corners of the cube and P at the body-centre. What is the formula of the
compound? What are the coordination numbers of P and Q?
1.13 Niobium crystallises in
body-centred cubic structure. If density is 8.55g cm–3, calculate
atomic radius of niobium using its atomic mass 93 u.
1.14 If the radius of the
octahedral void is r and radius of the atoms in closepacking is R, derive
relation between r and R.
1.15 Copper crystallises into a
fcc lattice with edge length 3.61 × 10–8 cm. Show that the
calculated density is in agreement with its measured value of 8.92 g cm–3.
1.16 Analysis shows that nickel
oxide has the formula Ni0.98O1.00.
What fractions of nickel exist as Ni2+ and Ni3+ ions?
1.17 What is a semiconductor?
Describe the two main types of semiconductors and contrast their conduction
mechanism.
1.18 Non-stoichiometric cuprous
oxide, Cu2O can be prepared in laboratory.In this oxide, copper
to oxygen ratio is slightly less than 2:1. Can you account for
the fact that this substance is a p-type semiconductor?
1.19 Ferric oxide crystallises in
a hexagonal close-packed array of oxide ions with two out of every three
octahedral holes occupied by ferric ions.Derive the formula of the ferric
oxide.
1.20 Classify each of the
following as being either a p-type or a n-type semiconductor:
(i) Ge doped with In (ii) B doped with Si.
1.21 Gold (atomic radius = 0.144
nm) crystallises in a face-centred unit cell.What is the length of a side of
the cell? .
[Ans.: 4.07 × 10–8 cm]
1.22 In terms of band theory, what
is the difference
(i) between a conductor and an insulator
(ii) between a conductor and a semiconductor?
1.23 Explain the following terms
with suitable examples:
(i) Schottky defect (ii) Frenkel defect (iii) Interstitials and
(iv) F-centres.
1.24 Aluminium crystallises in a
cubic close-packed structure. Its metallic radius is 125 pm.
(i) What is the length of the side of the unit cell?
(ii) How many unit cells are there in 1.00 cm3 of
aluminium?
[Ans.: (i) 354 pm; (ii) 2.26 × 1022]
1.25 If NaCl is doped with 10–3
mol % of SrCl2, what is the concentration of
cation vacancies?
1.26 Explain the following with
suitable examples:
(i) Ferromagnetism
(ii) Paramagnetism
(iii) Ferrimagnetism
(iv) Antiferromagnetism
(v) 12-16 and 13-15 group compounds.
SHORT
ANSWER TYPE QUESTION
Q.1.What is the no. of atom per
unit cell in a body centered structure?
Q.2.What is the no. of atom per
unit cell in a face centered structure?
Q.3.Why
are amorphous solids is isotropic is nature
Q.4.What is the co-ordination no.
in a rock salt type structure?
Q.5.What
is the coordination number of an octahedral void?
Q.6.What is the coordination no. of
an atom in a ccp crystal structure?
Q.7.What is the maximum possible
coordination no. of an atom in an hcp crystal structure of an element?
Q.8.What is the coordination number of a
tetrahedral void?
Q.9.State
the importance of voids in crystals.
Q.10.What is the no. of octahedral
& tetrahedral voids in a unit cell of ccp structure?
Q.11.Is the octahedral voids are
larger the tetrahedral voids? Give reason
Q.12.What is the no. of nearest
neighbour for give lattice point in a face centered cubic lattice?
Q.13.Name the non –stoichiometric
defect point defect responsible for colour in alkali halide.
Q.14.Explain the term dislocation
in relation to crystal.
Q.15..What type of lattice
imperfection found in crystals?
Q.16.Name the crystal defect which
lowers the density pof an ionic crystal.
Q.17.What makes the crystal of KCl
appears sometimes violet?
Q.18.Why is
KCl sometimes voilet instead of pure white?
Q.19.Why is
NaCl (common salt) sometimes yellow instead of pure white?
Q.20.Why
does ZnO appears yellow on heating?
Q.21.Why
are solids containing F-CENTRE are paramagnetic?
Q.22.Mention
one property which is caused due to the presence of F-CENTRE in a solid?
Q.23.What is the effect of Schottky
& Frenkel defect on the density of crystalline solid?
Q.24.Why the Frenkel defect is not
foun in pure alkali halide?
Q.25.Why does the Frenkel defect
not affect the density of AgCl?
Q.26.Why is Frenkel defect found in
AgCl?
Q.27.Name a substance which on
addition to AgCl causes cationic vacancy in it?
Q.28.What is the effect of Frenkel
defect on the electrical conductivity of the solid?
Q.29.What is the effect of presence
of Schottky defect on the density of a crystal?
Q.30.What type of substance exhibit
Schottky defect? Give two examples.
Q.31.Name the solid which contain
both Schottky & Frenkel defect?
Q.32.What
type of stoichiometric defect is shown by (i) ZnS and (ii) AgBr?
Q.33.Name the point defects which
lower the density?
Q.34.Name
the crystal defect produced when NaCl crystal is doped with MgCl2
Q.35.Out of CdCl2 &
NaCl which will produce Schottky defect, if added to AgCl crystal?
Q.36.What is doping? Why it is
done?
Q.37.Name an element with which
silicon can be doped to give n-type semiconductor.
Q.38.Name an element with which
silicon can be doped to give p-type semiconductor.
Q.39.Name an element with which
germanium can be doped to give n-type semiconductor.
Q.40.How does pure silicon, which is
an insulator, behave as semiconductor on heating?
Q.41.What may be the difference
between phosphorus & gallium dupped semiconductor?
Q.42.What cause the conduction of electricity
in semiconductor?
Q.43.What is
the effect of increasing temperature on the conductivity of semiconductors?
Q.44.Explain band model of
conductor, semiconductor & insulator?
Q.45.What is the effect of
temperature on electrical conductivity of the following substance:-
Metallic conductor , semiconductor &
insulator
Q.46.What is Curi temperature?
Q.47.What happen when ferromagnetic
substance is subjected to high temperature?
Q.48.What happens when
ferrimegnetic Fe3O4
is heated at 850k & why? (similar to 47)
Q.49.Why
is Fe3O4 ferrimagnetic at room temperature but becomes
paramagnetic at 850K?
Q.50.How can a ferromagnetic
substance be change to a paramagnetic one?
Q.51.Define photovoltaic compound?
.Q.52.
What is polymorphism?
Q.53.What
is a primitive unit cell?
Q.54.What is the % of free space in
BCC crystal?
Q.55.What is the % of free space in
FCC crystal?
Q.56.Calculate the packing fraction
of FCC crystal?
Q.57.How
many spheres are in contact with each other in a single plane of a close packed
structure?
Q.58.Name
two closest packed arrangements of identical spheres.
Q.59.What
is meant by long range order in crystals?
Q.60.Which
of the following lattices has the highest packing efficiency: (i) Simple cubic;
(ii) Body centered cubic and (iii)
Hexagonal close-packed lattice?
Q.61. Define the following terms:-
(a)Amorphous (b) Bravis lattice (c) Point
defects defect (d) Interstitials defect
(e)
Vacancy defect (f) Co-ordination
number (g) Voids
Q.62.
Differentiate the following
(A) Crystalline
& amorphous solid
(B) Schottky
defect & Frankel defect
(C) Isotropic
& anisotropic properties
(D)Metallic
& ionic solid
(E) Orthorhombic & monoclinic structure
(F) Ferro & ferri
magnetism
(G)Para &
ferromagnetism
(H) Paramagnetism and diamagnetism.
Q.63.Classify the following solids as metallic;
molecular, amorphous, covalent or ionic
(i) SO2 (ii) Diamond (iii)
I2 (iv) MgO (iv)
Ag (v)
Quartz (vi) Ar
Q.64.Comment on the following on the basis of
magnetic behaviour:-
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(a) (b) (c) |
NUMERICALS
Q.1.An element occurs in bcc
structure with the edge length 300pm. The density of the element is 5.2g cm-3.
How many atoms of the element does 200g of the element contain?
Ans:
- 2.84x1024atom
Q.2.Na crystallizes in the cubic
lattice & the edge of the unit cell is 430pm. Calculate the no. of atom
in a unit cell. (At. Mass of Na=23 d=0.9623)
Ans:-2 atom
Q.3.An metallic elements exist as
bcc crystal lattice. each edge of the unit cell is 288pm. The density of the
metal is 7.2gcm-3. How many atom & unit cell are there in 100g
of the metal? Ans:-1.1632x1024,
5.816x1023
Q.4.The density of the Cr metal is
7.2gcm-3. If the unit cell has length of 289pm, determine the type
of unit cell. (At. Mass of Cr=52u) Ans:-
(bcc)
Q.5.Determine the type of the
cubic lattice to which the iron crystal belongs if it cell has an edge
length of 286pm & the density of the iron crystal is 7.86g cm-3. (at. Mass
of Fe=56gmpol-1)
Ans:-bcc
Q.6.Unit cell of element has an
edge length 409pm. Deduce the type of crystal lattice. (At. Mass=108u and density=
10.5gcm-3) Ans:-z=4,
FCC
Q.7.An element A crystallizes in
FCC structure. 200g of the element has 4.12x1024 atoms. The density
of A is 7.2gcm-3. Calculate the edge length of the unit cell.
Ans:-299.8pm
Q.8.An element having bcc structure
has atomic mass 50u & density 6.81gcm-1. Calculate the edge
length of the unit cell. Ans:-289.6pm
Q.9.An element crystallizes in FCC
structure. Its density is 7.2gcm-3. 208g of its element has 4.283x1024
atoms. Calculate edge length of the unit cell. Ans:-300pm
Q.10.The length of the unit cell edge
of a bcc crystal is 352pm. Calculate the radius of an atom of a metal.
Ans:-152.416pm
Q.11.An element crystallizes in
simple cubic structure. Its density is 8gcm-3 & its 200g contain
24x1023 atoms. Calculate the edge length. Ans:-218pm
Q.12.An metal has a bcc crystal
lattice structure. The density of the metal is 5.91gcm-3. Find out
the volume of the unit cell. (At. Mass=50u) Ans:-2.809x10-23cm3
Q.13. Li metal crystal has bcc
structure. Its density is 0.53gcm-3
and its molar mass is 6.94gmol1. Calculate the volume of the unit
cell. Ans:-4.348x10-23cm3
Q.14.An element exists in bcc
structure with a cell edge of 288pm. If the density of the element is 7.2gcm-3,
what is the atomic mass of the element? Ans:-52gmol-1
Q.15.An element occurs in bcc
structure. It has an edge length of 250pm. Calculate the molar mass if
its density is 8gcm-3. Ans:-37.64g
mol-1
Q.16.An metal has a FCC crystal
lattice structure. The length of the unit cell is 404pm. What is the molar
mass of the metal atom if the density of the metal atom is 2.72gcm-3?
Ans: - 27gmol-1
Q.17.An element A crystallises in FCC
structure, 208g of this element has 4.283x1034 atoms. If the edge
length of the unit cell is 408pm calculate its density. Ans:-2.86gcm-3
Q.18. A FCC element (molar, mass = 604 g mol–1 has cell
edge 4.0 × 10–8 cm. Calculate its density (NA=
6.023 × 1023 mol–1).
[Ans.: 6.23 g cm–3]
Q.19. An element crystallizes in a structure having a FCC unit
cell of an edge 200 pm. calculate its density if 200 g of this element
contain 24 × 1023 atoms.
[Ans.: 41.6
g cm–3]
Q.20.Cu crystallises in FCC cubic
lattice & has a density of 8.930gcm-3 at 293K. Calculate the radius of copper
atom. Atomic mass of Cu=63.55u. Ans:
- 127.7pm
Q.21.Metallic gold crystallises in
a FCC lattice & has a density of 19.3gcm-3. Calculate the radius of gold
atom. (Atomic mass of Au=197u).
Ans:-144.2pm.
Q.22. A metallic element has a body central cubic lattice. Each
end of its unit cell is 2.88 × 10-8 cm.The density of the metal is
7.20 g cm-3.Calculate:-
(i) The volume of unit cell.
(ii) Mass of unit cell.
(iii) Number of atoms in 100 g of metal.
[Ans.:
(i) 2.39 × 10-23cm3 (ii) 1.72 × 10-22g
(iii) 1.162 × 1024 atoms]
Q.23. A metal crystallises into two cubic phases FCC and bcc,
whose unit lengths are 3.5 and 3.0 วบ respectively, Calculate the ratio of
the densities of FCC and bcc lattices. [Ans.:1.26]
Q.24. an element of atomic mass 98.5 g mol–1 occurs in FCC
structure. If its unit edge length is 500pm and its density is 5.22 g cm–3.
Calculate the value of Avogadro constant.
[Ans.:
6.03 × 1023 mol–1]
CONCEPTUAL
Q.1.A cubic solid is made up of two
element x & y. atom y bare at the corner the of the cube & x at body
centre. What is the formula of the compound?
Q.2.A compound formed by elements P and Q crystallises in cubic
structure where P atom are at
the corners of a cube and Q atoms are at the face centre. What
is the formula of the compound?
[Ans.: PQ3]
Q.3.In
the formula of a compound A2B, which site would be occupied by A
ions?
Q.4.If
the formula of an ionic compound is A+B-, can the A+ occupy all the
(i)
Tetrahedral voids
(ii)
Octahedral voids?
Q.5.In
Zinc Sulphide; ZnS which ions.
(i)
Occupy tetrahedral voids
(ii)
Form the close packed lattice?
Q.6.In
NaCl crystal, Cl - ions form the cubic close packing. What sites are
occupied by Na+ ion?
Q.7.Calculate the no. of atoms in a
cube based on unit cell having one atom at each corner & two atoms at each
diagonal?
HOTS
ONE MARK QUESTIONS
TYPE-I
1. Account for the following:
(i) Solids are rigid and have a definite volume. NCERT INTEXT QUESTION 1.1 & 1.2
(ii)Quartz is regarded as a crystalline solid.
(iii)Glass is regarded as an amorphous solid.
(iv)Crystalline solids are anisotropic in nature.
(v)Amorphous solids are isotropic in nature.
(vi)Stability of a crystal is reflected in the magnitude of its
melting point.
(vii)Ionic solids conduct electricity in molten state but not in
solid state.
(viii)Vacancies are introduced in an ionic solid when a solid of
higher valence is added as
an impurity in it.
(ix)The cation vacancies in certain crystals make them good
catalysts.
(x)Non-Stoichiometric sodium chloride is a yellow solid.
(xi) In a p-type semiconductor the current is said to more through
holes.
(xii) Conductivity of metals decreases with rise in temperature.
2. Explain why ionic and metallic crystals have higher heat of
vaporization than do covalent molecular solids?
[Hint: Electrostatic forces of attraction act
between the ions in ionic compounds and between
the lattice of metal cation and delocalized electrons in metallic
crystals which are stronger than
the van der Walls forces of attraction acting in covalent
molecular solids.]
3. One of the best electric insulator is solid sulphur. In terms
of electronic configuration, why is
sulphur an insulator?
[Hint: Sulphur consists of S8 molecules which have no free electrons unlike
metals. Therefore
it regarded as best electric insulator.
4. Metallic cerium occurs both as hexagonal and Face-centred cubic
close packed crystals. Would you expect the density of Face-centred cubic
close-packed cerium crystals to be much different from the density of hexagonal
close-packed cerium crystals why or why not?
[Hint: Both face-centred-cubic close-packed and hexagonal
close-packed crystals have the
same coordination numbers and packing fraction. So they have this
same densities.
TYPE:-II
1. Iron-changes from the body centred cubic lattice to the
face-centred cubic lattice at 1199 K. How would the density of iron change
during this transformation?
[Hint: In closest packed face-centred cubic lattice, the
coordination number in 12 whereas body
Centred-cubic lattice has only eight (8) nearest neighbours. The
smaller the number of nearest
neighbours. The less compact is the packing. Hence, BCC lattice
has less density than the FCC
Lattice.]
2. Why are Cu–Be alloys sometimes used in electric switches whose
circuits are closed and
opened frequently, instead of copper metal, which is much better
electric conductor than
Cu–Be alloy?
[Hint. Cu and Be form interstital solid solution which is
harder than copper and has more
melting point.]
3. Which one of the following statement is incorrect? Assign the
reason of your choice.
(a) The coordination number of each type of ion in CsCl crystal in
8.
(b) A metal that crystallizes in bcc structure is more compact as
compared the same metal
that crystallizes in cubic-close packed lattice.
(c) A unit cell of an ionic crystal shares some of its ions with
the other unit cells.
(d) The length of unit cell in NaCl in 522 pm (r Na += 95 pm, r cl
- =181 pm)
[Hint: (b) because bcc lattice has a coordination number of
8 and ccp arrangement has
a coordination number of 12 that makes later more compact.]
TYPE-III.
Problems
1. In corundum, oxide ions form hcp and Al3+ occupy two
third of octahedral voids. Find the formula Of corundum. [Ans.: Al2O3]
2. An ion oxide crystalies in hcp array of oxygen with two out of
three vacant octahedral voids
occupied by iron. Find the formula of iron oxide. [Ans.: Fe2O3]
3. A solid A+ B– has NaCl type close packed
structure. If the anion has a radius of 250 pm. What
should be the ideal radius for the cation? Can a cation C+
having a radius of 180 pm be stepped
into the tetrahedral void of the crystal A+B–? Give reason for
your answer.
4. r (Rb+) = 1.47 A°, r (Br–) = 1.95 A° r (I)
= 2.16 A°, Predict the probable geometry for Rb Br and RbI.
[Ans.: CsCl and NaCl type]
2
MARKS QUESTIONS
1. (a) What is meant by the term, ‘crystallinity of a solid’?
(b) Why is quartz regarded as a crystalline solid while glass an
amorphous solid?
2. “Stability of a crystal is reflected in the magnitude of its
melting point” justify the statement.
3. Explain with the help of diagrams the structural differences
between various types of cubic units Cells.
3. Explain how much portion of an atom located at (a) corner (b)
body centre and (c) face-centre
Of a cubic unit cell in part of its neighbouring unit-cell.
4. Explain the term ‘Unit Cell’. Name the parameters that
characterize a unit cell.
5. Explain:
(a) Ionic solids are hard and brittle
(b) Copper is malleable and ductile
6.Explain the term ‘crystal imperfections or crystal defects’.
Name the two types of crystal
Imperfections.
7. Define the term, ‘Point Defect’. Name the various types of
point defects.
8.What is meant by non-stoichiometric defect? Ionic solids which
have anionic vacancies due to metal-excess defect develop colour. Explain with
the help of a suitable example.
9..Explain how vacancies are introduced in a solid when a cation
of higher valence is added in it.
10. Explain the terms: (i) Intrinsic semiconductors and (ii)
Extrinsic semiconductors.
Hots11. Pure Silicon is an insulator.
Silicon doped with phosphorus is a semiconductor. Silicon doped With gallium is
also a semiconductor. What is the difference between the two doped silicon
Semiconductors?
12. How can you calculate the density of a crystal whose length of
the edge of the unit cell is
Known?
13.Cu is conducting as such while
coppersulphate is conducting only in molten state or in aqueous solution.
THREE MARK QUESTIONS
1. Give reasons for:
(i) Window panes of the old buildings are thick at the bottom.
(ii) Glass is considered a super cooled liquid.
(iii) Amorphous solids are isotopic is nature.
2.(i) What is the origin of magnetic moments associated with
electrons is atoms?
(ii) What is the (a) percentage of free space and (b) coordination
number of a sphere in the
following close packed structure.
(A) Hexagonal close pack.
(B) Body centered close pack.
3. Explain the basis of: (i) similarities and (ii) differences
between metallic and cubic crystals.
4. Write and explain three differences between consequences of
Schottky and Frenkel defects
Under the heads.
(i) Effect on density
(ii) Effect on electrical conductivity
(iii) Effect on stability of the crystal
Hots5. Account for the following:
(i) Zinc oxide on heating turns yellow.
(ii) Schottky defect decreases the dencity of a crystal.
(iii) The cation vacancies in certain crystals move them good
catalysts.
Hots6. Give reasons for: (Repeated)
(i) Non-stoichiometric sodium chloride is a yellow in colour.
(ii) Solids with F-centre are paramagnetic.
(iii) Doping of NaCl crystal with SrCl2 changes its
structure.
7. What is a semiconductor? Describe the two main types of
semiconductors and contrast their
Conductance mechanism.
8. A metallic element
crystallises into a lattice containing sequence of layers of ABABAB....
Anypacking of spheres leaves out voids in the lattice. Assume the radius of
every sphere to be ‘r’.Calculate:
(a) The number of spheres in this HCP unit cell.
(b) Volume of this HCP unit cell.
