INTERMOLECULAR-FORCES-OF-LIQUIDS-AND-SOLIDS

Intermolecular Forces; Liquids and Solids

• Presentation by Mrs. Maria Niña C. Cabrera

• Focus on understanding properties of liquids and solids, intermolecular forces, and molecular structure effects.

Learning Competencies (Week 1)

• Use kinetic molecular model to explain liquid and solid properties.

• Differentiate types of intermolecular forces.

• Explain properties of liquids: surface tension, viscosity, vapor pressure, boiling point, and molar heat of vaporization.

• Properties of water in relation to molecular structure and intermolecular forces.

• Describe structure distinctions between crystalline and amorphous solids.

Atoms and Molecules

• Oxygen Atom Composition: 8 protons, 8 neutrons, and 8 electrons.

• Water Molecule: 1 Oxygen atom (O) and 2 Hydrogen atoms (H), chemical formula H₂O.

Kinetic Molecular Theory of Matter (KMT)

• Definition: Matter is made of constantly moving particles with varying energy levels based on temperature.

• KMT helps understand the states of matter: solid, liquid, gas.

• Discusses arrangement, kinetic energy, particle motion, attractive forces, and intermolecular forces.

KMT and Properties of Matter

• Solid:

  • Particles are closely packed, vibrate in fixed positions.

  • High density, definite shape, and volume.

• Liquid:

  • Particles are close but can slide past one another, taking the shape of the container.

  • Relatively high density, incompressibility, ability to diffuse, exhibits surface tension, and capillary action.

• Gas:

  • Particles are far apart, move freely, and possess low density and high compressibility.

  • Diffusion: spontaneous mixing of particles due to random motion.

  • Effusion: gas particles passing through small openings.

5 Assumptions of KMT

1. Gases consist of large numbers of tiny particles, spaced far apart.

2. Collisions between gas particles are elastic.

3. Gas particles are in constant, rapid, random motion, possessing kinetic energy.

4. No forces of attraction exist between gas particles.

5. Temperature represents the average kinetic energy of the particles.

Intermolecular Forces of Attraction

• Intermolecular forces differ from intramolecular bonds, being weaker and dependent on particle types.

Types of Intermolecular Forces

1. Dipole-Dipole Forces: Attractive forces between polar molecules' oppositely charged poles.

2. Dipole-Induced Dipole Forces: Polar molecules induce a temporary dipole in nonpolar ones.

3. Ion-Dipole Forces: Attractions between ions and polar molecules (e.g., Na⁺ with water's negative pole).

4. London Dispersion Forces: Weak forces due to fluctuations in electron distribution, present in all molecules but significant in nonpolar ones.

5. Hydrogen Bonds: Strong forces occurring between molecules with N, O, or F bonded to H.

Properties of Liquids

• Surface Tension: Molecules at the surface are held tightly together, creating a tension effect, which diminishes with rising temperature.

• Viscosity: Measure of fluid resistance to flow; impacted by molecular shape and polarity. Higher viscosity = greater resistance (e.g., honey vs. water).

• Capillary Action: Spontaneous rise of liquids in narrow spaces, resulting from cohesive and adhesive forces.

• Vapor Pressure: Pressure exerted by vapor in equilibrium with its liquid/solid form; volatile substances have high vapor pressures.

• Vaporization: Transition of liquid to gas; includes evaporation (occurs below boiling point) and boiling (occurs at boiling point).

Properties of Water

• Uniquely exists as liquid, solid (ice), and gas (steam) under natural conditions.

• Notable properties include:

  • Density due to H-bonding.

  • High boiling point and specific heat.

  • Action as a solvent due to its polarity and strong intermolecular forces.

Properties of Solids

• Particles Arrangement: Strong attraction results in fixed positions for particles, leading to definite shape and volume.

• Movement: Limited to vibrational motion.

• Melting Point: Temperature at which a solid melts; correlated with strength of attractive forces.

• Classes of Solids:

  1. Crystalline Solids: Ordered particle arrangement, distinct geometric forms (e.g., salt).

  2. Amorphous Solids: Random particle arrangement, no definite shape (e.g., glass, rubber).