Question 14 Marks
Read the passage given below and answer the following questions from (i) to (v).
Chemical properties of a substance do not change withthe change of its physical state; but rate of chemicalreactions do depend upon the physical state. Many timesin calculations while dealing with data of experiments werequire knowledge of the state of matter. Therefore, itbecomes necessary for a chemist to know the physical laws which govern the behaviour of matter indifferent states. Intermolecular forces are the forces ofattraction and repulsion between interactingparticles (atoms and molecules). This termdoes not include the electrostatic forces thatexist between the two oppositely charged ionsand the forces that hold atoms of a moleculetogether i.e., covalent bonds.Attractive intermolecular forces are knownas van der Waals forces, in honour of Dutchscientist Johannes van der Waals (1837-1923) . van der Waals forces vary considerablyin magnitude and include dispersion forcesor London forces, dipole-dipole forces, anddipole-induced dipole forces. A particularlystrong type of dipole-dipole interaction ishydrogen bonding. Only a few elements canparticipate in hydrogen bond formation, therefore it is treated as a separatecategory.
Atoms and nonpolar molecules are electricallysymmetrical and have no dipole momentbecause their electronic charge cloud issymmetrically distributed. But a dipole maydevelop momentarily even in such atoms andmolecules. The temporary dipoles of two different atomattract each other. Similarly temporary dipolesare induced in molecules also. This force ofattraction was first proposed by the Germanphysicist Fritz London, and for this reasonforce of attraction between two temporary dipoles is known as London force. dispersion force forces are always attractive and interactionenergy is inversely proportional to the sixthpower of the distance between two interactingparticles (i.e.,$1/r ^6$ where r is the distancebetween two particles). These forces areimportant only at short distances (~500 pm)and their magnitude depends on thepolarisability of the particle.
Dipole-dipole forces act between the moleculespossessing permanent dipole. Ends of thedipoles possess “partial charges” and thesecharges are shown by Greek letter delta (δ).Partial charges are always less than the unitelectronic charge $(1.6\times 10^{–19} C)$. The polarmolecules interact with neighbouringmolecules. This interactionis stronger than the London forces but isweaker than ion-ion interaction because onlypartial charges are involved. The attractiveforce decreases with the increase of distancebetween the dipoles. As in the above case herealso, the interaction energy is inverselyproportional to distance between polarmolecules. Dipole-dipole interaction energybetween stationary polar molecules is proportional to $1/r^3$ and thatbetween rotating polar molecules is proportional to $1/r ^6$, where r is the distancebetween polar molecules.
Dipole–Induced Dipole Forcesare type of attractive forces operate betweenthe polar molecules having permanent dipoleand the molecules lacking permanent dipole.Permanent dipole of the polar moleculeinduces dipole on the electrically neutralmolecule by deforming its electronic cloud. Thus an induced dipole is developedin the other molecule. In this case alsointeraction energy is proportional to $1/r ^6$ where r is the distance between twomolecules. Induced dipole moment dependsupon the dipole moment present in thepermanent dipole and the polarisability of theelectrically neutral molecule.
Chemical properties of a substance do not change withthe change of its physical state; but rate of chemicalreactions do depend upon the physical state. Many timesin calculations while dealing with data of experiments werequire knowledge of the state of matter. Therefore, itbecomes necessary for a chemist to know the physical laws which govern the behaviour of matter indifferent states. Intermolecular forces are the forces ofattraction and repulsion between interactingparticles (atoms and molecules). This termdoes not include the electrostatic forces thatexist between the two oppositely charged ionsand the forces that hold atoms of a moleculetogether i.e., covalent bonds.Attractive intermolecular forces are knownas van der Waals forces, in honour of Dutchscientist Johannes van der Waals (1837-1923) . van der Waals forces vary considerablyin magnitude and include dispersion forcesor London forces, dipole-dipole forces, anddipole-induced dipole forces. A particularlystrong type of dipole-dipole interaction ishydrogen bonding. Only a few elements canparticipate in hydrogen bond formation, therefore it is treated as a separatecategory.
Atoms and nonpolar molecules are electricallysymmetrical and have no dipole momentbecause their electronic charge cloud issymmetrically distributed. But a dipole maydevelop momentarily even in such atoms andmolecules. The temporary dipoles of two different atomattract each other. Similarly temporary dipolesare induced in molecules also. This force ofattraction was first proposed by the Germanphysicist Fritz London, and for this reasonforce of attraction between two temporary dipoles is known as London force. dispersion force forces are always attractive and interactionenergy is inversely proportional to the sixthpower of the distance between two interactingparticles (i.e.,$1/r ^6$ where r is the distancebetween two particles). These forces areimportant only at short distances (~500 pm)and their magnitude depends on thepolarisability of the particle.
Dipole-dipole forces act between the moleculespossessing permanent dipole. Ends of thedipoles possess “partial charges” and thesecharges are shown by Greek letter delta (δ).Partial charges are always less than the unitelectronic charge $(1.6\times 10^{–19} C)$. The polarmolecules interact with neighbouringmolecules. This interactionis stronger than the London forces but isweaker than ion-ion interaction because onlypartial charges are involved. The attractiveforce decreases with the increase of distancebetween the dipoles. As in the above case herealso, the interaction energy is inverselyproportional to distance between polarmolecules. Dipole-dipole interaction energybetween stationary polar molecules is proportional to $1/r^3$ and thatbetween rotating polar molecules is proportional to $1/r ^6$, where r is the distancebetween polar molecules.
Dipole–Induced Dipole Forcesare type of attractive forces operate betweenthe polar molecules having permanent dipoleand the molecules lacking permanent dipole.Permanent dipole of the polar moleculeinduces dipole on the electrically neutralmolecule by deforming its electronic cloud. Thus an induced dipole is developedin the other molecule. In this case alsointeraction energy is proportional to $1/r ^6$ where r is the distance between twomolecules. Induced dipole moment dependsupon the dipole moment present in thepermanent dipole and the polarisability of theelectrically neutral molecule.
- Partial charges are always less than the unit electronic charge:
- $(1.6\times 10^{–19} C)$
- $(1.6\times 10^{–18} C)$
- $(1.6\times 10^{–17}C)$
- $(1.6\times 10^{–16} C)$
- Temporary dipoles are induced in molecules also. ,this force of attraction was first proposed by:
- Johannes van der Waals
- Fritz London
- Robert Boyle
- Joseph Lewis Gay Lussac
- Atoms and nonpolar molecules are electrically:
- Compositional
- Unsymmetrical
- Symmetrical
- All the above
- Partial Charges denoted by greek letter ….
- $\in$
- $\zeta$
- $\delta$
- $\eta$
- The attractive force … with the … of distance between the dipoles.
- Increase, increase
- Decrease, decrease
- Increase, decrease
- Decreases, increase
Answer
View full question & answer→- (a) $(1.6\times 10^{–19}C)$
- (b) Fritz London
- (c) Symmetrical
- (c) $\delta$
- (d) Decreases, increase