Important Questions On The Solid State

Solid is a state of matter in which the constituent particles are tightly packed together. Atoms, ions, and other particles can make up the component particles of a solid substance. Solids have a specific shape, mass, and volume as a result of strong and brief interactions between their components. Intermolecular distances in solids are short and the intermolecular forces are strong. The constituent particles in solid (atoms, molecules or ions) have fixed positions and can only oscillate about their mean positions. According to the nature of order present in the arrangement of their constituent particles, solids can be classified into two main types- crystalline or amorphous. In amorphous solids, the arrangement of constituent particles has short-range order, isotropic in nature and no sharp melting point while crystalline solids have a characteristic shape, with the constituent particles in the arrangement of long-range order, anisotropic in nature and a sharp melting point.

Solid State of Matter

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Very Short Answer Questions (1 Mark Questions)

Ques. A solid's density is increased by which point defect in its crystal units? 

Ans. The point defect in which crystal units increase the density of a solid is termed the interstitial defect.

Ques. How do metallic and ionic compounds conduct electricity differently? 

Ans. In metallic substances, electrical conductivity is owing to free electrons, whereas, in ionic substances, conductivity is related to the presence of ions.

Ques. How may an inherent semiconductor's conductivity be increased? 

Ans. Adding an acceptable amount of suitable contaminant increases conductivity. Intrinsic doping is the name given to this process.

Ques. When LiCl is heated in Li vapours, why does it turn pink?

Ans. This is due to a metal excess defect caused by anionic vacancies, in which unpaired electrons occupy anionic sites (F-centres).

Ques. What makes liquid and gases fluids? 

Ans. Liquid and gases are categorized as fluids because their particles may flow.

Ques. Give an example of a molecular solid and an ionic solid. 

Ans. Molecular solid → Iodine (I₂)

Ionic solid → Sodium Chloride (NaCl)

Ques. In solids, which type of ionic substances display the Schottky defect?

Ans. Highly ionic compounds that have a high coordination rjuniber and a small difference in the size of cations and anions show the Schottky defect.

Ques. What type of interactions is responsible for holding the molecules together in a polar molecular solid? 

Ans. Dipole-dipole forces of attraction are responsible for holding the molecules together in a polar molecular solid.

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Short Answer Questions (2 Marks Questions)

Ques. What causes solids to be incompressible? 

Ans. Solids are incompressible because their constituent particles (atoms, ions, or molecules) are densely packed in regions with very small interparticle gaps. If we try to condense the electron clouds of the constituent particles, repulsive interactions will take precedence.

Ques. In a bcc unit cell, how many atoms per unit cell (z) are there? 

Ans. The number of atoms in a unit cell of a body-centred cubic structure:

Contribution by 8 atoms on the corners

= 18 × 8 = 1

Contribution by the atom present within the body = 1

∴ Total number of atoms present in the unit cell = 1 + 1 = 2 atoms

Ques. Other than metallic shine, write a point of contrast between a metallic solid and an ionic solid. 

Ans. Metallic solids conduct electricity in their solid state, whereas ionic solids conduct electricity only in their molten state or in solution. Metals conduct electricity through electrons, while ionic substances conduct electricity through ions. Ionic solids are hard and brittle, whereas metallic solids are flexible and ductile.

Ques. Why is glass thought to be a super-cooled liquid? 

Ans. Although it is an amorphous solid, glass is classified as a supercooled liquid since it exhibits some of the characteristics of liquids. It is slightly thicker near the bottom, for example. This is only feasible if it has flowed like liquid, although slowly.

Ques. When a solid is heated, what kind of defect can occur? What physical property is influenced by it, and how? 

Ans. When a solid is heated, electrons become mobile, and when one is removed, and electron-deficient hole occurs, changing the solid's conductivity. It also has an effect on the magnetic characteristics of solids. When metallic solids are heated, their conductivity drops.

Ques. Why do ionic substances conduct electricity when they are molten but not when they are solid? 

Ans. The electrical conductivity of any ionic solid owes to the mobility of the ions. These are non-conducting in this state because ionic mobility is negligible in the solid-state. The ions present get some mobility as they melt. Thus, this is how ionic solids become conductors.

Crystalline and Amorphous Solids

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Long Answer Questions (3 Marks Questions)

Ques. Why do solids have a definite volume? 

Ans. Because they have weak intermolecular forces and the ions are not grouped in a regular pattern, gases and liquids can flow and take on the shape of their container. As a result, when they are subjected to a specific pressure or temperature, their ions or molecules rearrange and exhibit flow features. 

Solids, on the other hand, have ions or molecules grouped in a regular and repeating three-dimensional structure. As a result, when solids are subjected to pressure or heat, their ions or molecules do not rearrange themselves, and they do not exhibit flow qualities or have a definite volume.

Ques. Explain how an ionic solid gets vacancies when a cation with a higher valence is added as an impurity. 

Ans. A stoichiometric point defect is a vacancy defect. Such a flaw can be found in ionic solids. Some vacancies are generated in ionic solids when the ionic impurity has a different valence than the primary component.

When molten NaCl containing a little quantity of SrCl₂ crystallises, Sr²⁺ ions occupy some of the Na⁺ ions' sites. Each Sr²⁺ ion takes the place of two Na+ ions. The number of cationic vacancies created is the same as the quantity of Sr²⁺ ions.

Ques. What are the characteristics of Amorphous solid? 

Ans. The characteristics of amorphous solids are as follows: 

• They have an asymmetrical shape.
• They've placed a short-term order.
• They gradually soften as the temperature changes.
• They are isotropic in nature, which means they have identical physical properties in all directions.
• They are cut into two pieces with uneven surfaces when sliced with a sharp-edged instrument.
• They don't have a distinct fusion heat.
• Pseudo solids or super cooled liquids are the terms used to describe them. This is due to their proclivity towards flowing, although slowly.

Ques. Answer the following questions:

1. Classify the following solids on the nature of intermolecular forces: Benzene, Silver
2. Give the reason why AgCl shows Frenkel defect while NaCl does not.
3. What type of semiconductor will be formed when Ge is doped with Al? 

Ans. (a) Benzene is a Molecular solid (non-polar)

Silver is a Metallic solid

(b) The size of Ag+ is smaller than the larger Na+ ion of NaCl due to the intermediate radius of AgCl, so it can easily occupy interstitial spaces and shows Frenkel defect.

(c) a p-type semiconductor is formed when Ge is doped with Al.

Ques. What do you understand by a semiconductor? Brief about the two main types of semiconductors.

Ans. A semiconductor is defined as a solid material whose electrical conductivity lies between those of the typical metallic conductors and insulators. The semiconductors possess conductivity in the range of 102 to 10-9 ohm-1 cm-1.

These are two types of semiconductors majorly:

• n-type semiconductors: Doping of higher group element impurity results in the formation of n-type semiconductors.
• p-type semiconductors: The impurity of lower groups results in electron-deficient bonds in the structure and the electron deficiency develops in the p-hole.

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Very Long Answer Questions (5 Marks Questions)

Ques. Explain the different types of point defects. (5 marks )

Ans. Point defects can be divided into three categories:

• Stoichiometric Defects: The electrical neutrality of the material and the ratio of positive and negative ions (Stoichiometric) are unaffected by this type of point defect. The term "intrinsic" or "thermodynamic" faults are used to describe this type of flaw. They are separated into two groups: There are two sorts of defects: Vacancy defect and Interstitial defect.
• Frenkel Defect: The smaller ion (cation) moves out of its ionic solids site and into an intermolecular space, which is referred to as the Frenkel defect. The old position has a vacancy defect, whereas the new site has an interstitial defect in this circumstance.
• Schottky Defect: A sort of vacancy defect that can be seen in ionic solids is the Schottky defect. When it comes to ionic compounds. However, by eliminating an equal number of anions and cations, we can restore the complex's electrical neutrality. It reduces the density of the material. The cations and anions are approximately the same sizes in this situation.

Ques. What are the four types of crystalline solids? Explain.

Ans. The four types of crystalline solids are elaborated as follows: 

Ionic Solids:- 

• The constituent particles of an ionic solid are cations and anions. These ions are grouped in three-dimensional space in a uniform way. The formation of an ionic solid is the strong electrostatic attraction between cations and anions. 
• Sodium chloride (NaCl), potassium chloride (KCl), and lead bromide (PbBr₂) are examples of ionic solids.

Metallic Solids

• Metals such as iron, copper, gold, silver, sodium, and potassium exist as solids at room temperature. Metallic bonding is a strong gravitational pull that holds the atoms together in a metallic crystal. The metal occupies fixed locations in metallic crystals, although their electron shells migrate.

Covalent Solids

• Covalent solids are solids in which covalent bonds bind the atoms throughout the crystal. Covalent solids are also known by the following terms:

1. Atomic solids
2. Network solid
3. Macromolecular crystals
4. Giant molecules

Molecular Solids

• These are solids whose constituent particles are molecules. Molecular solids include things like iodine (I₂), ice (H₂O), dry ice (solid carbon dioxide), and naphthalene.

Ques. What type of materials, ferromagnetic or ferrimagnetic, would make better permanent magnets? 

Ans. A magnetic field attracts Ferromagnetic compounds such as iron, cobalt, nickel, gadolinium, and others very strongly, and these substances can be permanently magnetised. In the solid-state, the metal ions of ferromagnetic compounds are organised into tiny regions called domains. Each domain is a little magnet. The domains of a ferromagnetic substance that has not been magnetised are randomly orientated, and their magnetic moments are cancelled.

When the substance is exposed to a magnetic field, however, all of the domains align in the direction of the magnetic field, resulting in a significant magnetic effect. Even when the magnetic field is removed, the domain order remains. Magnetic fields attract ferromagnetic compounds on a weekly basis. As a result, ferromagnetic materials would be better permanent magnets.

Ques. Explain

(i) The basis for metallic and ionic crystals' similarities and differences.

(ii) Ionic solids are brittle and rigid. 

Ans. (i) The electrostatic force of attraction holds both metallic and ionic crystals together, which explains their similarities. The electrostatic force acts between the positive ions and the electrons in metallic crystals. It operates between the oppositely charged ions in ionic crystals. As a result, they both have high melting points.

The distinction between metallic and ionic crystals is that the electrons in metallic crystals are free to travel, allowing them to conduct electricity. The ions in ionic crystals, on the other hand, are not free to migrate. As a result, they are unable to conduct electrical current. However, in a molten state or in a liquid state, they do conduct electricity in an aqueous solution.

(ii) Ions are the particles that make up ionic crystals. The electrostatic force of attraction holds these ions together in three-dimensional patterns. The charged ions are held in place by the electrostatic force of attraction, which is quite powerful. Ionic crystals are hard and brittle because of this.

Ques. Describe the characteristics of the solid state.

Ans. The following characteristics determine the state of a solid. They're as follows:

• Specific Mass, Volume, and Structure

Solids have specific mass, volume, and structure because strong intermolecular interactions hold the constituent particles of matter together. The intermolecular force tends to overpower the thermal energy at low temperatures, so solids stay in a stable state.

For example: If you put a 10 cm cube of timber into a 13-mL beaker, it will keep its shape and volume, but if you pour 10 cm water into the beaker, it will keep its volume but change the form of the beaker and have a smooth surface.

• Intermolecular Distance Is Short

Because of the dense packing of constituent particles of matter in a solid, the intermolecular space between them is small. Strong intermolecular interactions keep the atoms and molecules close together.

• Intermolecular forces are extremely powerful

Because the constituent particles of matter are so close together, intermolecular interactions are particularly strong in solids.

• Densely Packed

Solids have a density that is greater than liquids and gases. Solids also have a high density since their volume is fixed.

• Solids are hard and incompressible

Solids are hard and incompressible in nature due to strong intermolecular forces that keep particles locked in their locations. Solids cannot be squeezed any farther since there is no gap between molecules.

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