Liquids, Solids, and Intermolecular Forces

Flashcards about Liquids, Solids, and Intermolecular Forces

Intermolecular Forces

Attractive forces that exist among the particles that compose matter.

Phase

A homogeneous part of the system in contact with other parts of the system but separated from them by a well-defined boundary.

Liquids Properties

Particles in a liquid are closely packed, have some ability to move around, are incompressible, take the shape of their container and flow, but don’t have enough freedom to escape or expand to fill the container.

Gases Properties

Complete freedom of motion; particles are not held together, are constantly flying around, bumping into each other and the container, a large amount of space between the particles, molar volume of the gas state of a material is much larger, compressible, can move to fill the entire container

Compressibility

Molecules closely spaced -not easily compressible; molecules widely spaced -highly compressible

Solids Properties

Particles are packed close together, fixed in position, though they may vibrate, incompressible, retain their shape and volume when placed in a new container and prevents the solid from flowing

Crystalline solids

Particles arranged in an orderly geometric pattern

Amorphous solids

Particles that do not show a regular geometric pattern over a long range

Intermolecular Forces

The structure of particles determines the strength of these forces which hold the substance together and determines the state of the substance.

Intermolecular forces

Attractive forces between molecules.

Intramolecular forces

Forces that hold atoms together in a molecule.

Types of Attractive Forces:

London Dispersion Forces, Dipole - Dipole, Hydrogen Bonding, Ion - Dipole

Dispersion Forces (LDF)

Electron movements create temporary dipole, induce the neighboring atoms/molecules to also have dipole resulting in weak electrostatic attraction.

Polarizability

The ease with which the electron distribution in the atom (or molecule) can be distorted

Size of the Instantaneous Dipole

Volume of the electron cloud, larger molar mass = more electrons = larger electron cloud = increased polarizability = stronger attractions; Shape of the molecule – More surface-to-surface contact = larger induced dipole = stronger attraction

Dipole– Dipole Attractions

Polar molecules interact with other polar molecules through attraction between negative and positive poles.

Trends in the Strength of Intermolecular Attraction

The stronger the attractions among the atoms or molecules, the more energy it will take to separate them. The higher the normal boiling point of the liquid, the stronger the intermolecular attractive forces.

Ion-Dipole Forces

Attractive forces between an ion and a polar molecule described by Coulombs law.

Hydrogen Bonds

A special case of dipole–dipole attractions and is stronger than other dipole–dipole attractions requiring a hydrogen bond donor and acceptor molecule.

Hydrogen Bond

A special dipole-dipole interaction between the hydrogen atom in a polar N-H, O-H, or F-H bond and an electronegative O, N, or F atom.

Special dipole-dipole interaction

Hydrogen bonds have a powerful effect on the structures and properties of many compounds (like DNA)

Basic properties of liquids

Viscosity, surface tension, and capillary action

Viscosity

The resistance to flow is determined by the strength of the intermolecular attractions and temperature.

Surface tension

A property of liquids that results from the tendency of liquids to minimize their surface area.

Capillary action

The ability of a liquid to flow up a thin tube against the influence of gravity caused by cohesive and adhesive forces.

Cohesion

Intermolecular attraction between like molecules

Adhesion

Attraction between unlike molecules

Melting, or fusion

The transition from the solid phase to the liquid phase.

Evaporation, or vaporization

The process of changing a liquid to a gas

Sublimation

Solids that enter the gas state directly

Deposition

Capturing of vapor molecules into a solid

Vaporization (liquid to gas)

Requires an input of energy

Condensation (gas to liquid)

Releases energy

Enthalpy of vaporization, ∆Hvap

The energy change for the vaporization of 1 mol of a liquid.

Enthalpy of fusion, ∆Hfus, and enthalpy of sublimation, ∆Hsub

Refer to the energy changes associated with the melting and sublimation, respectively, of 1 mol of a substance.

Heating Curve

A graph that shows how the temperature changes as the pure substance is heated.

Vapor Pressure

The pressure exerted by a vapor when it is in dynamic equilibrium with its liquid.

Critical temperature (Tc)

The temperature above which the gas cannot be made to liquefy, no matter how great the applied pressure.

Critical pressure (Pc)

The minimum pressure that must be applied to bring about liquefaction at the critical temperature.

Phase diagram

Shows the phase of a specific substance under all possible pressure–temperature combinations.

Triple point

Represents the P and T at which all three phases of the substance are in equilibrium.

Critical point

Occurs at the pressure and temperature conditions above which the substance no longer exists as either a liquid or gas.