Liquids and Solids: Properties & Intermolecular Forces

• The topic is the physical properties of liquids, intermolecular forces, and the distinctions between amorphous and crystalline solids.

Physical Properties of Liquids and Intermolecular Forces

• Surface tension measures the elastic force on a liquid's surface.
• Surfactants enhance spreading and penetrating properties by reducing surface tension.

Cohesive & Adhesive Forces

• Cohesive forces exist between molecules within a liquid leading to less attraction to other surfaces.
• Adhesive forces exist between molecules and the surface of another substance, resulting in greater attraction.
• Meniscus formation arises from cohesive and adhesive forces, forming either concave up or convex down shapes.

Viscosity

• Viscosity refers to a liquid's resistance to flow.
• Viscosity is inversely proportional to temperature and directly proportional to the strength of intermolecular forces (IMF).
• Viscosity is directly proportional to size and complexity.
• The SI unit for viscosity is pascal-second (Pa-s), with centipoise (cP) equal to 0.001 Pa-s.

Vapor Pressure

• Vapor pressure is the equilibrium pressure of a vapor above its liquid or solid state, where the evaporation rate equals the condensation rate.
• Molecules in vapor exert pressure by colliding with container walls.
• Equilibrium vapor pressure is exerted by gas and increases with high vapor pressure and temperature, where molecules, with enough kinetic energy, overcome IMF.
• Vapor pressure is inversely proportional to IMF, notably in dipole-dipole interactions.
• Stronger IMF is correlated with a greater amount of energy.

Molar Heat of Vaporization

• Molar heat of vaporization is the energy needed to vaporize one mole of liquid at a specific temperature.
• High intermolecular attraction necessitates high energy and heat of vaporization, as energy is required to free molecules from the liquid phase, measured at atmospheric pressure.

Boiling Point

• Boiling point occurs when vapor pressure equals external pressure.
• Normal boiling point is the temperature at which a liquid converts to gas at 1 atm.
• Higher evaporation rates result in higher boiling points.

Amorphous and Crystalline Solids

Classes of Solids

• Crystalline solids are composed of numerous small crystals with a definite geometrical shape and exhibit rigidity and incompressibility.
• Crystalline solids feature long-range order of particles in a repeated arrangement and are considered "true solids".
• Crystalline solids possess a definite heat of fusion and a sharp melting point, transitioning immediately to a liquid upon melting.

Properties of Crystalline Solids

• The unit cell is the basic repeating unit of crystalline solids.
• Atoms or molecules at lattice points are identically arranged.
• In most metals, lattice points are occupied by atoms.
• Crystalline solids often display a plane of symmetry in their structure.
• Crystal structures are stabilized by intermolecular forces and exhibit well-defined order in three dimensions, with geometric shapes reflecting attractive intermolecular forces.

Crystals

Ionic Crystals

• Composed of charged ions.
• Characterized by hardness and high melting points due to strong electrostatic forces.
• Poor electrical conductors in solid form but good conductors when melted.
• Subject to brittleness due to the breakage of attractive forces.

Metallic Crystals

• Held by electrostatic forces.
• Good conductors with high melting points.
• Lustrous, or shiny.

Molecular Crystals

• Have lattice points occupied by molecules.
• Intermolecular forces include London Dispersion forces and Hydrogen bond forces.
• Exhibit weak intermolecular forces.

Covalent Crystals

• Feature strong intermolecular forces.
• Poor electrical conductors.
• Can be made into one type of atom.
• Have very high melting points.

Amorphous Solids

• Amorphous solids lack well-defined shape and regular atomic arrangement.
• Amorphous solids behave as fake solids, pseudo-solids, or supercooled liquids.
• Amorphous solids can be molded and blown into various shapes, behaving like crystals at certain temperatures.
• Glass is the most versatile example of an amorphous solid.
• Amorphous solids shatter irregularly and lack sharp melting points, melting across a wide range of temperatures.
• Amorphous solids might contain impurities and exhibit weak intermolecular forces.

Phase Diagram

• Illustrates conditions under which a particular state is stable, physical states under different conditions of temperature and pressure, with the Y-axis representing pressure and the X-axis representing temperature.

Regions

• Solid phase occurs at low temperature and high pressure, found on the left side of the graph, indicating where phase changes start.
• Liquid phase occurs at moderate temperature and pressure, centrally located on the graph.
• Vapour/Gas phase occurs at high temperature and low pressure.

Boundaries

• At boundaries, a line represents a combination of pressure and temperature where phases beside each other are at equilibrium.
• The red/first line divides solid and gas phases, and the blue/last line divides liquid and solid.
• The red/first line indicates sublimation and deposition, the green/second line indicates melting and freezing.
• The blue/last line indicates evaporation and condensation.

Points

• A triple point represents both the temperature and pressure at which all three phases coexist in equilibrium.
• A critical point is where liquid and gaseous phases merge into a single supercritical fluid where liquid and gas are indistinguishable.

Explore liquids' physical properties, including surface tension, cohesive and adhesive forces, and viscosity. Understand the role of intermolecular forces. Learn the differences between amorphous and crystalline solids and their unique characteristics.