Intermolecular Forces

• London dispersion forces are the weakest intermolecular forces and occur between all molecules.
• Intermolecular forces are possible between atoms or molecules in condensed phases such as dispersion forces, dipole-dipole attractions, and hydrogen bonding.
• The types of intermolecular forces experienced by specific molecules can be identified based on their structures.
• The relation between the intermolecular forces present within a substance and the temperatures associated with changes in its physical state can be explained.
• The extent of the rise (or fall) is directly proportional to the surface tension of the liquid and inversely proportional to the liquid’s density and the tube’s radius.
• Depending upon the relative strengths of adhesive and cohesive forces, a liquid may rise (such as water) or fall (such as mercury) in a glass capillary tube.
• Adhesive and cohesive forces can be distinguished.
• Viscosity, surface tension, and capillary rise can be defined.
• Intermolecular attractive forces play roles in each of these properties/phenomena.
• The principal difference between the condensed states (liquids and solids) and the gaseous state is the distance between molecules.
• A phase is a homogeneous part of the system in contact with other parts of the system but separated from them by a well-defined boundary.
• Uncondensed Phase refers to widely separated molecules in constant chaotic motion.
• Gas refers to weak forces between molecules.
• Condensed Phase refers to molecules that are closer.
• Liquid refers to attractive forces that are strong enough to hold molecules close together but weak enough so molecules move relative to each other.
• Solid refers to strong forces that lock molecules in place, have a fixed position, and are incompressible.
• The boiling points of substances often reflect the strength of the intermolecular forces operating among the molecules.
• Intermolecular forces are generally weaker than intramolecular forces.
• London dispersion forces are temporary fluctuations in the electron distributions within atoms and nonpolar molecules that could result in the formation of short-lived instantaneous dipole moments.
• The extent to which a dipole moment can be induced in a molecule is called its polarizability.
• Intramolecular forces hold atoms together in a molecule.
• It usually requires much less energy to evaporate a liquid than to break the bonds in the molecules of the liquid.
• Intermolecular forces are attractive forces between molecules.
• At the boiling point, enough energy must be supplied to overcome the attractive forces among molecules before they can enter the vapor phase.
• The strengths of London dispersion forces also depend significantly on molecular shape because shape determines how much of one molecule can interact with its neighboring molecules at any given time.
• London dispersion forces are responsible for the general trend toward higher boiling points with increased molecular mass and greater surface area in a homologous series of compounds, such as the alkanes.
• In general, the melting points of substances increase with the strength of the intermolecular forces.
• Dispersion forces increase with molecular weight.
• Larger the atoms → Larger electron clouds → more polarizable.
• Condensation forms when water vapor is cooled enough to form liquid water, such as on the outside of a cold beverage glass or in the form of fog.
• Gaseous butane is compressed within the storage compartment of a disposable lighter, resulting in its condensation to the liquid state.
• Matter is made of particles that are constantly in motion (Kinetic Energy).
• Capillary action occurs when a liquid flows within a porous material due to the attraction of the liquid molecules to the surface of the material and other liquid molecules.
• Surface tension results from the cohesive forces between molecules at the surface of a liquid.
• The adhesive forces between the liquid and the porous material and the cohesive forces within the liquid may be strong enough to move the liquid upward against gravity.
• Surface tension is defined as the energy required to increase the surface area of a liquid, or the force required to increase the length of a liquid surface by a given amount.
• Among common liquids, water exhibits a distinctly high surface tension due to strong hydrogen bonding between its molecules.
• Capillary action can also occur when one end of a small diameter tube is immersed in a liquid.
• The smaller the diameter of the tube is, the higher the liquid climbs.
• Wine wicks up a paper towel because of the strong attraction of water (and ethanol) molecules to the −OH groups on the towel’s cellulose fibers and the strong attraction of water molecules to other water molecules.