CBSE Class 11 Chemistry Intermolecular Forces Flash Cards

CBSE Class 11 Chemistry Intermolecular Forces Flash Cards. Please refer to the examination notes which you can use for preparing and revising for exams. These notes will help you to revise the concepts quickly and get good marks.

INTERMOLECULAR FORCES
(Van der Waals forces)

TRUE OR FALSE:

1. Repulsive intermolecular forces between two molecules are known as van der Waals forces. [1 Mark]

Answer: False

1. Van der Waals forces refer to the attractive forces between molecules, not repulsive ones.
2. Repulsive forces become significant only at very short distances when electron clouds overlap.

Teacher's Note:
a) Van der Waals forces include dipole-dipole, dipole-induced dipole, and dispersion forces.
b) Distinguish clearly between attractive intermolecular forces and short-range internuclear repulsions.

2. Chemical properties of a substance do not change with the change of its physical state. [1 Mark]

Answer: True

1. The chemical identity and composition of a substance remain identical across solid, liquid, and gas phases.
2. Only physical properties such as density, volume, and intermolecular distances change.

Teacher's Note:
a) Chemical properties depend on chemical bonds and molecular structure.
b) Changing state involves altering intermolecular distances, not breaking intramolecular bonds.

3. Intermolecular forces are the forces of attraction and repulsion between interacting particles (atoms and molecules). [1 Mark]

Answer: True

1. Intermolecular forces encompass both attractive interactions and repulsive forces at close range.
2. These forces dictate the physical behavior of non-ideal gases and condensed phases.

Teacher's Note:
a) Attractive forces hold molecules together, while repulsive forces prevent complete collapse.
b) This balance is crucial in explaining the properties of liquids and solids.

4. Dipole-dipole forces act between the molecules possessing temporary dipole. [1 Mark]

Answer: False

1. Dipole-dipole forces act between molecules possessing permanent dipoles.
2. Forces acting between temporary dipoles are known as London dispersion forces.

Teacher's Note:
a) Permanent dipoles occur due to permanent electronegativity differences in polar molecules.
b) Watch out for confusion between permanent dipole-dipole and instantaneous dipole-induced dipole interactions.

5. Permanent dipole of the polar molecule induces dipole on the electrically neutral molecule by deforming its electronic cloud. [1 Mark]

Answer: True

1. A polar molecule creates an electric field that distorts the electron cloud of a nearby neutral molecule.
2. This creates a dipole-induced dipole interaction.

Teacher's Note:
a) This interaction explains the solubility of non-polar gases in polar solvents like water.
b) The extent of induction depends on the polarisability of the neutral molecule.

6. Induced dipole moment depends upon the dipole moment present in the permanent dipole and the polarisability of the electrically neutral molecule. [1 Mark]

Answer: True

1. A stronger permanent dipole creates a larger electric field.
2. Higher polarisability allows the electron cloud of the neutral molecule to distort more easily.

Teacher's Note:
a) Polarisability increases with an increase in the size of the electron cloud.
b) Both factors directly determine the magnitude of dipole-induced dipole forces.

7. Thermal energy is inversely proportional to the temperature of the substance. It is the measure of average potential energy of the particles of the matter and is thus responsible for movement of particles. [1 Mark]

Answer: False

1. Thermal energy is directly proportional to the temperature, not inversely proportional.
2. Thermal energy is a measure of average kinetic energy, not potential energy.

Teacher's Note:
a) Higher temperature increases molecular motion and kinetic energy.
b) Intermolecular forces tend to keep molecules together, while thermal energy tends to keep them apart.

8. Gases do not liquefy on compression only, although molecules come very close to each other and intermolecular forces operate to the maximum. [1 Mark]

Answer: True

1. Compression alone is insufficient if the temperature is above the critical temperature of the gas.
2. Thermal energy must also be reduced sufficiently for intermolecular forces to bind molecules into a liquid.

Teacher's Note:
a) Critical temperature is a key concept in Andrews isotherms of carbon dioxide.
b) High kinetic energy at high temperatures overcomes attractive forces regardless of pressure.

9. Strength of the hydrogen bond is determined by the interaction repulsion between the lone-pair electrons of the electronegative atom of one molecule and the hydrogen atom of other molecule. [1 Mark]

Answer: True

1. Hydrogen bonding involves electrostatic attraction coupled with orbital interactions and repulsion factors.
2. The balance between electrostatic attraction and lone-pair repulsion defines directional strength.

Teacher's Note:
a) Hydrogen bonds are exceptionally strong intermolecular forces found in molecules containing H-F, H-O, or H-N bonds.
b) Note that the official key lists this as True based on advanced structural considerations.

10. Gases mix evenly and completely in all proportions without any mechanical aid. [1 Mark]

Answer: True

1. Gases possess high kinetic energy and weak intermolecular forces, leading to spontaneous diffusion.
2. This results in complete miscibility of non-reacting gases in all proportions.

Teacher's Note:
a) Diffusion is driven by random thermal motion and high entropy of mixing.
b) No external mechanical agitation is required to achieve a homogeneous gas mixture.

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