Types of bonding and Forces in solid Questions in English

(C) In metallic bonds,the valence shell electrons are delocalised and shared between many atoms.
These delocalised electrons allow the metal atoms to slide past one another without being subjected to strong repulsive forces.
The malleability and ductility of metals is due to this sliding capacity of the layers of metal ions.

(C) Graphite is a soft solid lubricant that is extremely difficult to melt.
This is because graphite has a layered structure where carbon atoms are arranged in large hexagonal plates (rings) held together by strong covalent bonds within the layers,while the layers themselves are held together by weak van der Waals forces (interplate bonds).
These weak interplate bonds allow the layers to slide over each other,making it a lubricant,while the strong covalent bonds within the layers require very high temperatures to break,making it difficult to melt.

(C) The lustre of metals is due to the presence of free or mobile electrons in the metallic lattice.
When light strikes the surface of the metal,these mobile electrons absorb the energy of the incident light and then re-emit it.
This reflection of light by the mobile electrons gives the metal its characteristic shiny appearance or lustre.

(B) The enthalpy of solution $(\Delta H_{\text{sol}})$ is given by the sum of the lattice enthalpy and the enthalpy of hydration:
$\Delta H_{\text{sol}} = \Delta H_{\text{lattice}} + \Delta H_{\text{hyd}}$
Given: $\Delta H_{\text{lattice}} = +788 \ kJ \ mol^{-1}$ and $\Delta H_{\text{hyd}} = -784 \ kJ \ mol^{-1}$
$\Delta H_{\text{sol}} = 788 \ kJ \ mol^{-1} + (-784 \ kJ \ mol^{-1}) = +4 \ kJ \ mol^{-1}$

(D) Network solids (also known as covalent solids) are formed by the formation of covalent bonds between adjacent atoms throughout the crystal. $AlN$,diamond,$ZnS$,and $SiO_2$ are network solids. (Note: $ZnS$ is often classified as a network solid due to its covalent character). Thus,the number of network solids is $4$.
Ionic solids are formed by the three-dimensional arrangement of cations and anions held by strong electrostatic forces. $CaF_2$,$MgO$,and $NaCl$ are ionic solids. Thus,the number of ionic solids is $3$.
$H_2O$ (ice) and $CCl_4$ are molecular solids.
$Cu$ and $Ag$ are metallic solids.
Therefore,the number of network solids and ionic solids is $4$ and $3$ respectively.

(C) Dipole-induced dipole interactions occur between a polar molecule (possessing a permanent dipole) and a non-polar molecule (lacking a permanent dipole).
The permanent dipole of the polar molecule distorts the electron cloud of the non-polar molecule,inducing a dipole in it.
$NH_3$ is a polar molecule,while $H_2$ is a non-polar molecule. Therefore,dipole-induced dipole interactions exist between them.
$H_2O$ and $C_2H_5OH$ are both polar,exhibiting dipole-dipole interactions.
$Cl_2$ and $CCl_4$ are both non-polar,exhibiting London dispersion forces.
$SiF_4$ and $BF_3$ are non-polar due to their symmetrical structures,exhibiting London dispersion forces.

(A) The interaction energy between stationary dipoles is proportional to $1 / r^3$.
For rotating polar molecules,the interaction energy is proportional to $1 / r^6$ (often referred to as Keesom forces).
Therefore,the correct proportionality is $1 / r^3$ for stationary and $1 / r^6$ for rotating molecules.

(C) In $diamond$,each carbon atom is $sp^3$ hybridized and bonded to $4$ other carbon atoms in a rigid,three-dimensional tetrahedral network. This structure prevents the movement of atoms,making it extremely hard.
In $graphite$,each carbon atom is $sp^2$ hybridized,forming planar hexagonal layers. These layers are held together by weak $van \ der \ Waals$ forces,which allow the layers to slide over each other,making $graphite$ soft.

(C) Silicon carbide $(SiC)$ is a covalent solid (also known as a network solid).
In this structure,silicon and carbon atoms are linked by covalent bonds in a three-dimensional network.
$MgO$ is an ionic solid,$Mg$ is a metallic solid,and $CaF_2$ is an ionic solid.

(B) Lattice enthalpy of an ionic solid is defined as the energy required to completely separate $1 \ mol$ of a solid ionic compound into its gaseous constituent ions.
For $NaCl_{(s)}$,the process is represented as:
$NaCl_{(s)} \longrightarrow Na^{+}_{(g)} + Cl^{-}_{(g)}$
Thus,the enthalpy change of this reaction $(\Delta_r H)$ corresponds to the lattice enthalpy of $NaCl_{(s)}$.

(C) In the solid state,$PCl_{5}$ undergoes auto-ionization to form an ionic lattice consisting of tetrahedral $[PCl_{4}]^{+}$ cations and octahedral $[PCl_{6}]^{-}$ anions.
The reaction is: $2PCl_{5}(s) \longrightarrow [PCl_{4}]^{+}(s) + [PCl_{6}]^{-}(s)$.