Type of solid and Their properties Questions in English

(C) Quartz $(SiO_2)$ is a network solid where silicon and oxygen atoms are linked together by a continuous network of covalent bonds. Therefore,it is classified as a covalent or network solid.

(D) Isotropy is the property of exhibiting the same physical properties in all directions.
Amorphous solids are isotropic in nature because their constituent particles are arranged randomly,leading to identical properties in all directions.
In contrast,crystalline solids are anisotropic.

(D) Graphite consists of layers of carbon atoms arranged in a hexagonal lattice,where layers are held together by weak van der Waals forces.
Cadmium iodide $(CdI_2)$ also exhibits a layered structure where layers of $I^-$ ions are held together by van der Waals forces with $Cd^{2+}$ ions occupying octahedral holes.
Therefore,both graphite and cadmium iodide possess a layered crystal structure.

(A) Amorphous solids are isotropic in nature,meaning their physical properties (such as refractive index,electrical conductivity,etc.) are the same in all directions. $Glass$ is an amorphous solid,whereas $Sodium$ (a metal) and $Lime$ $(CaO)$ are crystalline solids,which are anisotropic. Therefore,$Glass$ is the correct answer.

(B) Anisotropy is a property exhibited by crystalline solids,where physical properties like refractive index,electrical conductivity,and thermal expansion vary with the direction of measurement.
Among the given options,$Barium \ chloride$ $(BaCl_2)$ is a crystalline solid,whereas glass,wood,and paper are amorphous solids.
Therefore,$Barium \ chloride$ will show anisotropy.

(B) Amorphous solids are often referred to as pseudo solids or supercooled liquids because they do not have a long-range order of particles.
Rubber,glass,and plastics are common examples of amorphous solids.
$CaF_2$ and $NaCl$ are crystalline solids,which possess a regular,repeating arrangement of particles.
Therefore,rubber is the correct answer.

(B) Ionic solids consist of ions held together by strong electrostatic forces of attraction.
These forces are significantly stronger than the intermolecular forces found in molecular solids or the forces in amorphous solids.
While covalent network solids (like diamond) also have very high melting points,in the context of general classification,ionic solids are characterized by high melting points due to their rigid crystal lattice structure.

(B) The correct answer is $B$.
Crystalline solids are characterized by a regular and repeating pattern of constituent particles (atoms,ions,or molecules) that extends throughout the entire three-dimensional structure of the solid.
This is known as $ \text{long-range order} $.
In contrast,amorphous solids exhibit only $ \text{short-range order} $.

(D) The energy gap (band gap) is the energy difference between the valence band and the conduction band.
For conductors,the gap is zero or negligible.
For semiconductors,the gap is small (typically $0.5 \ eV$ to $3 \ eV$).
For insulators,the gap is very large.
Among the given options:
$B$ (Boron) is a metalloid/non-metal with a large gap.
$Zn$ (Zinc) is a metal,but in the context of solid-state band theory,$Ge$ (Germanium) is a well-known semiconductor with a small band gap of approximately $0.67 \ eV$.
$Cl$ (Chlorine) is a non-metal insulator with a very large gap.
Therefore,$Ge$ has the smallest energy gap among the choices provided.

(A) In semiconductors,the energy gap between the valence band and the conduction band is small.
At low temperatures,electrons are unable to jump to the conduction band.
As the temperature increases,more electrons gain sufficient thermal energy to jump from the valence band to the conduction band.
This increase in the number of charge carriers leads to an increase in the conductivity of semiconductors.

(A) An intrinsic semiconductor is a pure semiconductor material without any significant dopant species present. $Ge$ (Germanium) and $Si$ (Silicon) are group $14$ elements that act as intrinsic semiconductors in their pure form. $Ga-As$ is a compound semiconductor,and $Ge-Ga$ represents a doped semiconductor. Therefore,$Ge$ is the correct answer.

(B) The electrical conductivity of semiconductors is low at room temperature.
By adding a small amount of appropriate impurity (a process known as $Doping$),the number of charge carriers (electrons or holes) increases significantly.
This process increases the electrical conductivity of the semiconductor.

(A) $Ge$ is a group $14$ element.
$As, P, Sb,$ and $Bi$ are group $15$ elements.
When a group $14$ element is doped with a group $15$ element,there is an extra electron available after forming four covalent bonds with the neighboring $Ge$ atoms.
This excess electron increases the conductivity of the semiconductor,resulting in an $n-$ type semiconductor.

(B) Silicon $(Si)$ belongs to group $14$ of the periodic table,which has $4$ valence electrons.
Boron $(B)$,Aluminum $(Al)$,and Gallium $(Ga)$ belong to group $13$,which has $3$ valence electrons.
When $Si$ is doped with group $13$ elements,there is a deficiency of one electron in the crystal lattice,creating an electron hole.
Since the charge carriers are positive holes,the resulting semiconductor is a $p-$type semiconductor.

(A) In $n$-type semiconductors,the doping is done with group $15$ elements (like $P$ or $As$) in a group $14$ element (like $Si$ or $Ge$).
This results in an excess of electrons.
Therefore,the conduction of electricity is primarily due to the movement of these extra electrons.

(B) In $p$-type semiconductors,the doping is done with group $13$ elements (like $B$,$Al$,$Ga$) into group $14$ elements (like $Si$,$Ge$).
This creates electron-deficient sites known as holes.
These holes act as charge carriers,and the movement of electrons into these holes results in the conduction of electricity.
Therefore,the conduction in $p$-type semiconductors is primarily due to holes.

(C) Intrinsic semiconductors like $Si$ or $Ge$ are group $14$ elements. To create $p$-type semiconductors,they are doped with group $13$ elements,which are trivalent (having $3$ valence electrons). This creates an electron hole,which acts as a charge carrier.

(A) Substances that show permanent magnetism are called ferromagnetic substances.
$Fe_3O_4$ (magnetite) is a well-known ferromagnetic substance used in making permanent magnets.
$MnO$ is antiferromagnetic,while $Gd$ (Gadolinium) is ferromagnetic but $Fe_3O_4$ is the standard textbook example for permanent magnets.

(B) $CrO_2$ is a metal oxide that exhibits metallic conductivity like metals. It also shows ferromagnetic properties,which makes it useful in the manufacture of magnetic tapes.

(D) Ferromagnetic substances are those that are strongly attracted by a magnetic field. $Fe_3O_4$ (magnetite) and ferrites like $MgFe_2O_4$ are examples of ferrimagnetic substances,which show strong attraction due to unequal alignment of magnetic moments. However,$ZnFe_2O_4$ is an example of an antiferromagnetic substance where the magnetic moments of the domains are aligned in such a way that they cancel each other out,resulting in zero net magnetic moment. $Fe_2O_3$ is also known to exhibit ferrimagnetism or antiferromagnetism depending on the phase. Among the given options,$ZnFe_2O_4$ is specifically classified as antiferromagnetic.

(A) Antiferromagnetic substances possess domain structures similar to ferromagnetic substances,but their domains are oppositely oriented and cancel out each other's magnetic moment.
$MnO$ (Manganese$(II)$ oxide) is a classic example of an antiferromagnetic substance.
$TiO_2$ is diamagnetic.
$VO_2$ and $CrO_2$ are ferromagnetic.

(A) Ferroelectric materials are those that possess a permanent electric dipole moment even in the absence of an external electric field.
$BaTiO_3$ (Barium titanate) is a well-known example of a ferroelectric material.
In $BaTiO_3$,the $Ti^{4+}$ ion is displaced from the center of the octahedral void,creating a permanent dipole moment.

(C) When mechanical stress is applied to certain crystals,they produce electricity due to the displacement of ions. This phenomenon is known as $piezoelectricity$.

(B) The phenomenon in which a substance exists in more than one form is known as $Polymorphism$.
If the substance is an element,it is specifically called $Allotropy$.
However,in the context of general solid-state chemistry,$Polymorphism$ is the term used for compounds existing in multiple crystalline forms.

(B) Amorphous solids are those in which the constituent particles do not have a long-range ordered arrangement.
Glass is a classic example of an amorphous solid (often called a supercooled liquid).
Diamond,rock salt $(NaCl)$,and $CaCO_3$ are crystalline solids with a well-defined,long-range ordered structure.

(B) Glass is an amorphous solid,which is primarily composed of silica $(SiO_2)$,lime $(CaO)$,and sodium carbonate $(Na_2CO_3)$.
These components are fused together at high temperatures to form ordinary soda-lime glass.

(C) In the solid state,$N_2O_5$ exists as the nitronium nitrate salt,which is composed of $[NO_2]^+$ and $[NO_3]^-$ ions.
Therefore,it is an ionic solid.
$BrF_5$ is a covalent molecule,$S_4N_4$ is a covalent cage structure,and $NO$ is a covalent gas.

(A) The setting of cement is a complex process involving the hydration of its constituents.
$C_3A$ (Tricalcium aluminate) sets the fastest,causing flash set.
$C_3S$ (Tricalcium silicate) is responsible for early strength.
$C_2S$ (Dicalcium silicate) hydrates very slowly and is responsible for the development of strength over a long period.
Therefore,$C_2S$ sets at the slowest rate.

(B) The existence of a substance in more than one solid modification is known as polymorphism.
For example,sulphur is a polymorphic substance,its two polymorphic forms are rhombic and monoclinic sulphur.

(C) $C_6H_6$ is diamagnetic $(i-5)$.
$CrO_2$ is ferromagnetic $(ii-3)$.
$MnO$ is antiferromagnetic $(iii-1)$.
$Fe_3O_4$ is ferrimagnetic $(iv-2)$.
$Fe^{3+}$ is paramagnetic with $5$ unpaired electrons $(v-4)$.

(A) The stability of a crystal depends upon the strength of the interparticle attractive force.
The melting point of a solid is a measure of the energy required to overcome these attractive forces.
Therefore,a higher melting point indicates stronger interparticle forces,which corresponds to higher crystal stability.
Thus,the stability of a crystal is reflected in the magnitude of its melting point,and the Reason correctly explains the Assertion.

(C) Ferromagnetic and ferrimagnetic substances possess ordered magnetic domains at room temperature.
On heating,the thermal energy increases,which leads to the randomisation of the magnetic moments (spins).
This randomisation results in the loss of the ordered magnetic structure,causing the substance to become paramagnetic.
The reason provided is incorrect because the electrons do not change their intrinsic spin; rather,the alignment of the spins becomes random due to thermal agitation.

(N/A) The intermolecular forces of attraction present in solids are very strong. The constituent particles of solids have fixed positions and cannot move from their mean positions. They can only oscillate about their mean positions. This is the reason why solids are rigid.

(B) The intermolecular forces of attraction present in solids are very strong.
The constituent particles of solids have fixed positions,meaning they are rigid and cannot move freely.
Because the particles are held tightly in fixed positions,solids maintain a definite volume.

(N/A) Amorphous solids: Polyurethane,teflon,cellophane,polyvinyl chloride,fibre glass.
Crystalline solids: Naphthalene,benzoic acid,potassium nitrate,copper.

(N/A) An isotropic solid has the same value of physical properties when measured along different directions.
Therefore,the given solid,having the same value of refractive index along all directions,is isotropic in nature.
Hence,the solid is an amorphous solid.
When an amorphous solid is cut with a sharp-edged tool,it cuts into two pieces with irregular surfaces,meaning it does not show the cleavage property.

(N/A) The classification of the given solids based on the nature of intermolecular forces is as follows:
$1$. Potassium sulphate $(K_2SO_4)$: Ionic solid
$2$. Tin $(Sn)$: Metallic solid
$3$. Benzene $(C_6H_6)$: Molecular (non-polar) solid
$4$. Urea $(NH_2CONH_2)$: Polar molecular solid
$5$. Ammonia $(NH_3)$: Polar molecular solid
$6$. Water $(H_2O)$: Hydrogen bonded molecular solid
$7$. Zinc sulphide $(ZnS)$: Ionic solid
$8$. Graphite $(C)$: Covalent or network solid
$9$. Rubidium $(Rb)$: Metallic solid
$10$. Argon $(Ar)$: Non-polar molecular solid
$11$. Silicon carbide $(SiC)$: Covalent or network solid

(B) The given properties,such as being very hard,acting as an electrical insulator in both solid and molten states,and having an extremely high melting point,are characteristic of a covalent or network solid.
In these solids,atoms are linked by a continuous network of covalent bonds.
Examples of such solids include diamond $(C)$ and quartz $(SiO_2)$.

(N/A) In ionic compounds,electricity is conducted by the movement of ions.
In the solid state,ions are held together by strong electrostatic forces of attraction and are not free to move throughout the crystal lattice.
Therefore,ionic solids act as insulators in the solid state.
However,in the molten state or when dissolved in a polar solvent,the crystal lattice breaks down,and the ions become free to move,allowing them to conduct electricity.

(C) Metallic solids are characterized by the presence of a sea of delocalized electrons,which makes them good electrical conductors. Due to the non-directional nature of metallic bonds,they are also malleable and ductile.

(B) An $n-$type semiconductor conducts electricity due to the presence of extra electrons.
Since group $14$ elements have $4$ valence electrons,doping them with a group $15$ element (which has $5$ valence electrons) introduces an extra electron into the crystal lattice.
Therefore,a group $14$ element is converted into an $n-$type semiconductor by doping it with a group $15$ element.

(A) Ferromagnetic substances make better permanent magnets.
In the solid state,the metal ions of ferromagnetic substances are grouped together into small regions called domains. Each domain acts as a tiny magnet.
In an unmagnetised piece of a ferromagnetic substance,the domains are randomly oriented,causing their magnetic moments to cancel out.
However,when the substance is placed in an external magnetic field,all the domains align in the direction of the magnetic field,producing a strong magnetic effect.
This alignment of the domains persists even after the removal of the external magnetic field,thereby making the ferromagnetic substance a permanent magnet.

(N/A) Amorphous solids are solids whose constituent particles are arranged in an irregular pattern and possess only short-range order.
These solids are isotropic in nature and melt over a range of temperature.
Because of this,they are sometimes referred to as pseudo solids or supercooled liquids.
They do not have a definite heat of fusion.
When cut with a sharp-edged tool,they break into pieces with irregular surfaces.
Examples of amorphous solids include $glass$,$rubber$,and $plastic$.

(N/A) The arrangement of the constituent particles makes glass different from quartz. In glass,the constituent particles have short-range order,whereas in quartz,the constituent particles have both long-range and short-range orders.
Quartz can be converted into glass by heating it to a high temperature and then cooling it rapidly (quenching).

(N/A) The classification of the given solids is as follows:
$1$. Ionic: $(ii)$ $(NH_{4})_{3}PO_{4}$ and $(x)$ $LiBr$ (composed of ions held by electrostatic forces).
$2$. Metallic: $(viii)$ Brass (an alloy) and $(ix)$ $Rb$ (alkali metal).
$3$. Molecular: $(i)$ $P_{4}O_{10}$,$(iv)$ $I_{2}$,and $(v)$ $P_{4}$ (composed of discrete molecules held by van der Waals forces).
$4$. Network (Covalent): $(iii)$ $SiC$,$(vii)$ Graphite,and $(xi)$ $Si$ (composed of atoms linked by a continuous network of covalent bonds).
$5$. Amorphous: $(vi)$ Plastic (lacks a long-range ordered structure).

(N/A) The stability of a crystal is directly related to the magnitude of its melting point. $A$ higher melting point indicates stronger intermolecular forces of attraction,which leads to greater stability of the crystal lattice.
The melting points of the given substances are:
$1$. Solid water: $273 \ K$
$2$. Ethyl alcohol: $158.8 \ K$
$3$. Diethyl ether: $156.85 \ K$
$4$. Methane: $89.34 \ K$
Conclusion: Based on the melting point values,the intermolecular forces are strongest in solid water due to hydrogen bonding and weakest in methane due to weak London dispersion forces.

(N/A) $(i)$ The basis of similarities between metallic and ionic crystals is that both these crystal types are held by electrostatic forces of attraction. In metallic crystals,the electrostatic force acts between positive metal ions and delocalized electrons. In ionic crystals,it acts between oppositely charged ions. Consequently,both types generally possess high melting points.
The basis of differences is that in metallic crystals,electrons are free to move,allowing them to conduct electricity in the solid state. In ionic crystals,ions are held in fixed positions and are not free to move; therefore,they are insulators in the solid state but conduct electricity in the molten state or in aqueous solution.
$(ii)$ The constituent particles of ionic crystals are ions held together in a three-dimensional lattice by strong electrostatic forces of attraction. Because these forces are very strong and directional,the ions are locked in fixed positions,making the crystals hard. They are brittle because the application of an external force can shift the layers of ions,causing like-charged ions to come close to each other,resulting in strong electrostatic repulsion that causes the crystal to fracture.

(N/A) Semiconductors are substances having conductance in the intermediate range of $10^{-6}$ to $10^{4} \ ohm^{-1} \ m^{-1}$.
The two main types of semiconductors are:
$(i)$ $n$-type semiconductor
$(ii)$ $p$-type semiconductor
$n$-type semiconductor: The semiconductor whose increased conductivity is a result of negatively-charged electrons is called an $n$-type semiconductor. When the crystal of a group $14$ element such as $Si$ or $Ge$ is doped with a group $15$ element such as $P$ or $As$,an $n$-type semiconductor is generated.
$Si$ and $Ge$ have four valence electrons each. In their crystals,each atom forms four covalent bonds. On the other hand,$P$ and $As$ contain five valence electrons each. When $Si$ or $Ge$ is doped with $P$ or $As$,the latter occupies some of the lattice sites in the crystal. Four out of five electrons are used in the formation of four covalent bonds with four neighbouring $Si$ or $Ge$ atoms. The remaining fifth electron becomes delocalised and increases the conductivity of the doped $Si$ or $Ge$.
$p$-type semiconductor: The semiconductor whose increased conductivity is a result of electron holes is called a $p$-type semiconductor. When a crystal of group $14$ elements such as $Si$ or $Ge$ is doped with a group $13$ element such as $B$,$Al$,or $Ga$ (which contains only three valence electrons),a $p$-type semiconductor is generated.
When a crystal of $Si$ is doped with $B$,the three electrons of $B$ are used in the formation of three covalent bonds and an electron hole is created. An electron from the neighbouring atom can come and fill this electron hole,but in doing so,it would leave an electron hole at its original position. The process appears as if the electron hole has moved in the direction opposite to that of the electron that filled it. Therefore,when an electric field is applied,electrons will move toward the positively-charged plate through electron holes. However,it will appear as if the electron holes are positively-charged and are moving toward the negatively-charged plate.

(A) $(i)$ $Ge$ (a group $14$ element) is doped with $In$ (a group $13$ element). Since $In$ has one less valence electron than $Ge$,a hole is created,resulting in a $p$-type semiconductor.
$(ii)$ $Si$ (a group $14$ element) is doped with $B$ (a group $13$ element). Similar to the first case,$B$ has one less valence electron than $Si$,creating a hole,which also results in a $p$-type semiconductor.