General Chemistry

• An atom consists of a nucleus, which contains protons and neutrons, and electrons that orbit the nucleus.
• Types of intermolecular forces

  • Dipole-dipole
  • Ion-dipole
  • London dispersion
  • Hydrogen bonding
• Differentiation between crystalline and amorphous solids

  Crystalline solids have a regular repeating pattern while amorphous solids lack a regular structure
• Different types of intermolecular forces

  1. Attractive forces between neighboring particles of one or more substances

  2. Pull the particles together

  3. Types: dipole-dipole, ion-dipole, London dispersion, hydrogen bonding
• Hydrogen bonds are about five to ten times stronger than other dipole-dipole attractions
• Hydrogen bonds are a special type of dipole-dipole interaction and only exist in molecules containing a hydrogen atom bonded to a small, highly electronegative atom such as N, O, or F
• Van der Waals forces are the intermolecular forces of attraction in a pure substance
• When two polar molecules are brought close together, the dipole charge of one molecule will be attracted to that of another
• Dipole-dipole forces exist between polar molecules where each molecule has unequal electron densities, resulting in a partial positive and partial negative end
• London dispersion forces


  • Exist between all atoms or molecules. The only forces acting in nonpolar molecules. They arise from continuous movement of electrons in particles. Attractions between an instantaneous (temporary dipole) dipole and an induced dipole which can induce the neighboring molecules
• Boiling point


  The temperature at which its vapor pressure is equal to the external or atmospheric pressure. The greater the attractive forces, the higher the kinetic energy needed to increase the kinetic energy of the molecules to break these forces
• Hydrogen bond


  • A special type of dipole-dipole interaction. Exists only in molecules that contain a hydrogen atom bonded to a small, highly electronegative atom such as N, O, or F. About five to ten times stronger than other dipole-dipole attractions
• Surface tension


  The property of liquid to resist an external force and thus assume a lesser surface area. Attributed to the strong attractive and cohesive forces between and among the molecules, particularly at the surface of the liquid
• Viscosity


  The resistance of a liquid to flow. It is loosely referred to as the thickness of thinness of a liquid. The greater the intermolecular force, the more viscous the substance
• Polarity


  The distribution of electrical charge among the atoms connected by a chemical bond. It can be polar, non-polar or ionic depending on the electronegativities of the atoms or molecules
• Ion-dipole forces


  • Acts between an ion and a polar molecule. Ions are dispersed amidst polar molecules. Cations interact more strongly with dipoles than Anions of the same magnitude of charge since they are smaller
• General properties of liquid affected by intermolecular force

  • Surface tension
  • Viscosity
  • Vapor pressure
  • Boiling point
  • Heat of vaporization
• (Molar) heat of vaporization


  The amount of heat required to vaporize one mole of a substance at its boiling point. It is determined by the strength of the molecular forces between molecules. The application of heat disrupts the intermolecular forces of attraction of the liquid molecules and allows them
• Amorphous Solid


  Have considerable disorder in their structure
• The application of heat disrupts the intermolecular forces of attraction of the liquid molecules and allows them to vaporize
• Amorphous Solid


  Components are not arranged in regular arrays
• Phase diagram is useful in determining the combination of temperature and pressure at which a substance will exist as a solid, liquid, or gas, or the conditions at which two phases exist in equilibrium
• For water, the triple point occurs at a specific temperature (0.01°C) and pressure (0.060 atm)
• The slope of these lines indicates the phase transitions between solid, liquid, and gas phases
• For water, the critical point is at approximately 373.99°C and 217.75 atm
• Heat required to vaporize one mole of a substance at its boiling point is determined by the strength of the molecular forces between molecules
• Crystalline Solid


  Have regular ordered arrays of components held together by uniform intermolecular forces
• Phase changes occur with increased temperature
• Triple Point: The point where the three phases (solid, liquid, and gas) coexist in equilibrium.
• Critical Point: At temperatures and pressures beyond a certain point, the distinction between the liquid and gas phases becomes blurred
• Phase Boundaries: The lines on the phase diagram represent phase boundaries
• Phase diagram is a graphical representation of the pressure-temperature relationships that apply to the equilibria between the phases of a substance
• Sublimation is the transition of a substance from the solid phase to the gaseous phase without changing into the liquid phase
• Phase Boundaries


  Lines on the phase diagram representing phase boundaries. The slope of these lines indicates how temperature or pressure affects the equilibrium between phases. The steeper the slope, the more sensitive the phase transition is to changes in that variable
• Properties of liquids affected by intermolecular forces

  • Surface tension
  • Viscosity
  • Vapor pressure
  • Boiling point
  • Heat of vaporization
• A solution is a homogeneous mixture of two or more substances composed of a solute and a solvent. The concentration of a solution is a measure of the amount of solute in a given amount of solvent or solution and can be expressed in percent mass, percent by volume, percent by mass-volume
• Solutions may be described as unsaturated, saturated, or supersaturated depending on the amount of solute present in the solution at the given temperature
• Solution


  Homogeneous mixture of two or more substances composed of a solute and a solvent
• Solvent

  Dissolving medium
• Mole fraction

  Ratio of the moles of the solute to the moles of the solution