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The Solid State : Important Questions And Answers

List of Questions and Answers

Q 1. What are the characteristics of solid state?

(i) They have definite mass, volume and shape.
(ii) Intermolecular distances are short.
(iii) Intermolecular forces are strong.
(iv) Their constituent particles (atoms, molecules or ions) have fixed positions and can only oscillate about their mean positions.
(v) They are incompressible and rigid.

Q 2. Examples of crystalline solids.

Metallic elements like Iron, copper and silver; non – metallic elements like sulphur, phosphorus and iodine and compounds like sodium chloride, zinc sulphide and naphthalene form crystalline solids

Q 3. What are crystalline solids?

A crystalline solid usually consists of a large number of small crystals, each of them having a definite characteristic geometrical shape. In a crystal, the arrangement of constituent particles (atoms, molecules or ions) is ordered. It has long range order which means that there is a regular pattern of arrangement of particles which repeats itself periodically over the entire crystal. Sodium chloride and quartz are typical examples of crystalline solids.

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Q 4.What are amorphous solids?


An amorphous solid (Greek amorphous = no form) consists of particles of irregular shape. The arrangement of constituent particles (atoms, molecules or ions) in such a solid has only short range order. In such an arrangement, a regular and periodically repeating pattern is observed over short distances only. Such portions are scattered and in between the arrangement is disordered.
Glass, rubber and plastics are typical examples of amorphous solids.

Q 5. Difference between crystalline and amorphous solids.


Crystalline Solids Amorphous Solids
Definite characteristic geometrical shape Irregular shape
Melt at a sharp and characteristic temperature Gradually soften over a range of temperature
When cut with a sharp edged tool, they split into two pieces and the newly generated surfaces are plain and smooth When cut with a sharp edged tool, they cut into two pieces with irregular surfaces
They have a definite and characteristic heat of fusion They do not have definite heat of fusion
Anisotropic in nature Isotropic in nature
True solids Pseudo solids or super cooled liquids
Long range order Only short range order.

Q 6. Why glass panes fixed to windows or doors of old buildings are found to be thicker at the bottom?

Glass panes fixed to windows or doors of old buildings are found to become thicker at the bottom because the glass flows down very slowly and makes the bottom portion thicker.

Q 7. Why are solids rigid?

Solids are rigid because the intermolecular forces of attraction that are present in solids are very strong. The constituent particles of solids cannot move from their positions they can only oscillate from their mean positions.

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Q 8. Classify the following as amorphous or crystalline solids: Polyurethane, naphthalene, benzoic acid, teflon, potassium nitrate, cellophane, polyvinyl chloride, fibre glass, copper.

Polyurethane - amorphous solids
Naphthalene - crystalline solids
Benzoic acid - crystalline solids
Teflon - amorphous solids
Potassium nitrate - crystalline solids
Cellophane - amorphous solids
Polyvinyl chloride - amorphous solids
Fibre glass - amorphous solids
Copper - crystalline solids

Q 9. Why is glass considered a super cooled liquid?

Glass is an amorphous solids and amorphous solids have a tendency to flow, through very slowly. That is why they are called supercooled liquid.

Q 10. 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?

Amorphous solids are isotropic in nature. It is because there is no long range order in them and arrangement is irregular along all the directions. Therefore, value of any physical property would be same along any direction. Amorphous solids will not show any cleavage property.

Q 11. Categorize Crystalline solids?

Crystalline solids can be classified on the basis of nature of intermolecular forces operating in them into four categories mainly,
metallic and
covalent solids.

Q 12. What are molecular solids?

Molecules are the constituent particles of molecular solids.They are divided into following categories:
1.Non polar Molecular Solids:They comprise of either atoms, for example, argon and helium or the molecules formed by non polar covalent bonds for example H2, Cl2 and I2.These solids are soft and non-conductors of electricity. They have low melting points and are usually in liquid or gaseous state at room temperature and pressure

2.Polar Molecular Solids:The molecules of substances like HCl, SO2, etc. are formed by polar covalent bonds. The molecules in such solids are held together by relatively stronger dipole-dipole interactions. These solids are soft and non-conductors of electricity.Their melting points are higher than those of non polar molecular solids yet most of these are gases or liquids under room temperature and pressure. Solid SO2 and solid NH3 are some examples of such solids.

3.Hydrogen Bonded Molecular Solids:The molecules of such solids contain polar covalent bonds between H and F, O or N atoms. Strong hydrogen bonding binds molecules of such solids like H2O (ice). They are non-conductors of electricity. Generally they are volatile liquids or soft solids under room temperature and pressure.

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Q 13. Explain Ionic solids?

Ions are the constituent particles of ionic solids. Such solids are formed by the three dimensional arrangements of cations and anions bound by strong coulombic (electrostatic) forces. These solids are hard and brittle in nature. They have high melting and boiling points. Since the ions are not free to move about, they are electrical insulators in the solid state. However, in the molten state or when dissolved in water, the ions become free to move about and they conduct electricity.

Q 14. Explain Metallic solids?

Metals are orderly collection of positive ions surrounded by and held together by a sea of free electrons. These electrons are mobile and are evenly spread out throughout the crystal. Each metal atom contributes one or more electrons towards this sea of mobile electrons. These free and mobile electrons are responsible for high electrical and thermal conductivity of metals. When an electric field is applied, these electrons flow through the network of positive ions. Similarly, when heat is supplied to one portion of a metal, the thermal energy is uniformly spread throughout by free electrons. Another important characteristic of metals is their lustre and colour in certain cases. This is also due to the presence of free electrons in them. Metals are highly malleable and ductile.

Q 15. Explain covalent or network solids?

Covalent bonds are strong and directional in nature, therefore atoms are held very strongly at their positions. Such solids are very hard and brittle. They have extremely high melting points and may even decompose before melting. They are insulators and do not conduct electricity. Diamond and silicon carbide are typical examples of such solids.

Q 16. 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.

Potassium sulphate : Ionic solid
Tin : Metallic solid
Benzene : non polar molecular solid
Urea : polar molecular solid
Ammonia : polar molecular solid
Water: hydrogen bonded molecular solid
Zinc sulphide : Ionic solid
Graphite : Covalent or network solids
Rubidium : Metallic solid
Argon : non polar molecular solid
Silicon carbide : Covalent or network solids.

Q 17. 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?

The properties specified above are of a covalent or network solid. Therefore, the given solid is a covalent or network solid. Diamond and quartz (SiO2) are examples for covalent or network solid.

Q 18. Ionic solids conduct electricity in molten state but not in solid state. Explain.

The constituent particles of ionic solid are not free to move in solid state. Therefore ionic solid are insulator in solid state. Ions becomes free to move in molten state so ionic solid can conduct electricity in molten state.

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Q 19.What type of solids are electrical conductors, malleable and ductile?

Metallic solids.

Q 20.What is crystal lattice?

Crystalline solids has a regular and repeating pattern of constituent particles.If its represented in a 3d form diametrically as shown below : Each particle represents a point and the arrangement is called crystal lattice.

Q 21.What is Bravais Lattices?

The 3D form of crystalline solids can be represented in 14 possible lattices which is called as Bravais Lattices.

Q 22.What are the characteristics of crystal lattice?

(a) Each point in a lattice is called lattice point or lattice site.
(b) Each point in a crystal lattice represents one constituent particle which may be an atom, a molecule (group of atoms) or an ion.
(c) Lattice points are joined by straight lines to bring out the geometry of the lattice.

Q 23.What is a unit cell in crystal lattice?

Unit cell is the smallest portion of a crystal lattice which, when repeated in different directions, generates the entire lattice.

Q 24.Name the parameters that characterise a unit cell in crystal lattice?

(i) its dimensions along the three edges, a, b and c. These edges may or may not be mutually perpendicular.
(ii) angles between the edges, α (between b and c) β (between a and c) and γ (between a and b). Thus, a unit cell is characterised by six parameters, a, b, c, α, β and γ.
Refer below figure for ref:

Q 25.What are primitive unit cells?

When constituent particles are present only on the corner positions of a unit cell, it is called as primitive unit cell.

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Q 26.What are centered unit cells?

When a unit cell contains one or more constituent particles present at positions other than corners in addition to those at corners, it is called a centred unit cell.
Centered unit cells are of 3 types:
a).Body centered unit cells: When a unit cell contains one or more constituent particles present at positions other than corners in addition to those at corners, it is called a centred unit cell.
b).Face centered unit cells:Such a unit cell contains one constituent particle present at the centre of each face, besides the ones that are at its corners.
c).End-centered unit cells:In such a unit cell, one constituent particle is present at the centre of any two opposite faces besides the ones present at its corners.

Q 27.Give the significance of a "lattice point".

Each lattice point represents one constituent particles of crystal. Particles of a solid may be an atom, a molecule, or an ion.

Q 28.Distinguish between
(i) Face-centred and end-centred unit cells.


Face-centred unit cell end-centred unit cells
Such a unit cell contains one constituent particle present at the centre of each face, besides the ones that are at its corners. In such a unit cell, one constituent particle is present at the centre of any two opposite faces besides the ones present at its corners

Q 29.Explain how much portion of an atom located at (i) corner and (ii) bodycentre of a cubic unit cell is part of its neighbouring unit cell.

(i) Atom of corner of a cubic unit cell is shared by eight adjacent unit cells.
Therefore, portion of the atom at the corner = 8 × 1/8 = 1 atom.

(ii) The atoms present at the center of the body is not available to its neighboring unit cell.
Therefore, portion of the atom at the center = 1 atom

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Q 30.What type of defect can arise when a solid is heated? Which physical property is affected by it and in what way?

When solid is heated it leads to vacancy defect.Vacancy defect gets created when some of the lattice sites are vacant.Vacancy defect makes the density of the solid weak.

Q 31.What type of stoichiometric defect is shown by AgBr ,Agl and ZnS?

ZnS shows Frenkel defect.
AgI shows Frenkel defect.
AgBr shows Frenkel defect and Schottky defect.

Q 32.Which stoichiometric defect in crystals increases the density of a solid?

Interstitial defect raises the density of crystal.