Chem

• Kinetic Molecular Theory


  The idea that matter is composed of tiny particles that are always in motion
• Kinetic Molecular Theory


  • Explains why matter exists in different phases (solid, liquids, and gas) and how matter can change from one phase to another
  • The state of the substance depends on the balance between the kinetic energy of the individual particles and the intermolecular forces
• Postulates of Kinetic Molecular Theory

  • Matter is made of particles that are constantly in motion. This energy in motion is called kinetic energy
  • The amount of kinetic energy in a substance is related to its temperature. Increased temperature means greater speed
  • There is space between particles. The amount of space between particles is related to the substance's state of matter
  • Phase changes happen when the temperature of the substance changes sufficiently
  • There are attractive forces in between particles called intermolecular forces. The strength of these forces increases as partides get closer together
• Intramolecular


  Forces that hold atoms together in a molecule. Intramolecular forces stabilize individual molecules. Generally, these forces are simply chemical bonds such as ionic and covalent bonding
• Intermolecular forces


  Attractive forces between molecules. Intermolecular forces are responsible for the non-ideal behavior of gases, but they exert more influence in the condensed phases of matter-liquids and solds
• Types of Intermolecular Forces

  • Dipole-dipole
  • London dispersion forces
  • Hydrogen bonding
  • Ion-dipole forces
• London Dispersion Forces


  The weakest intermolecular forces of attraction between all atoms and molecules. Dispersion forces are the only kind of intermolecular forces present among symmetrical nonpolar substances such as O2 and CO2, and monoatomic species such as noble gases
• Dipole-dipole Forces


  Attractive forces between polar molecules, between molecules that possess dipole moments. Their origin is electrostatic, and they can be understood in terms of Coulomb's law. The larger the dipole moment, the greater the force
• Hydrogen Bonding


  A special case of very strong dipole-dipole interaction. Strong Hydrogen bonding occurs among polar covalent molecules containing H and one of the three small, highly electronegative elements-F, O, or N. Hydrogen bond is about five to ten times stronger than other dipole-dipole interactions
• Ion-Dipole Forces


  A dipole force acts between an ion (either cation or anion) and a polar molecule. When an ionic compound is placed in an aqueous solution, the positive end of the ionic compound becomes surrounded by the partial negative end of the ionic compound. Ion dipole interactions are involved in the dissolution process, like in the case of sodium chloride (table salt) dissolving in water
• Surface Tension


  The force that causes the surface of a liquid to contract. It is the property of the surface of a liquid that allows it to resist an external force due to the cohesive nature of its molecules. Temperature affects surface tension - an increase in the liquid's temperature causes water molecules at the surface to evaporate, resulting in the weakening of the force of attraction
• Capillary Action


  The tendency of a liquid to rise in narrow tubes or be drawn into small openings such as those between grains of a rock. Capillary action is a result of the intermolecular attraction between the liquid and solid materials
• Types of Forces in Capillary Action

  • Cohesion - the intermolecular attraction between like molecules (the liquid molecules)
  • Adhesion - an attraction between unlike molecules
• Vapor Pressure

  Vaporization is a phase change from liquid to gas, while the opposite process (gas to liquid) is condensation. When liquid molecules break free from their neighbors and escape Into the gas phase, the process is called evaporation. Substances that evaporate readily are volatile - they have weak intermolecular forces of attraction
• Molar Heat of Vaporization


  The energy required to vaporize 1 mole of a liquid at a given temperature. It is a measure of the strength of intermolecular forces in a liquid. If the intermolecular attraction is strong, it takes a lot of energy to free the molecules from the liquid phase, and the heat of vaporization will be high
• Boiling Point


  The temperature at which the liquid changes into a gas. The boiling point is the temperature at which the vapor pressure of a liquid is equal to the external pressure. The boiling point depends on the external pressure - the higher the molar heat of vaporization, the higher the boiling point