L12: Forces & Solutions

In Lesson 12 we will investigate two separate topics: Intermolecular Forces and Solutions. Intermolecular Forces are very different from Intramolecular Forces.  We have seen in previous lessons that Intramolecular Forces are the strong chemical bonding forces that exist between the atoms of an ionic compound or covalent molecule. Ionic bonds are strong bonds between metal and nonmetal atoms. Metals tend to give up electrons and become positive ions called cations. Nonmetals tend to gain electrons and become negative ions called anions. Cations and anions are held together by the attraction of their electrostatic charges. Covalent bonds are strong bonds that form between nonmetal atoms that share electrons. Covalent bonds can be polar if the shared electrons are more likely to be found around one of the atoms.  Intermolecular forces are not as strong as the Intramolecular forces of chemical bonds. Intermolecular forces are weak attractions between molecules.  There are three types of intermolecular forces: dipole-dipole interactions, hydrogen bonding, and dispersion forces. Intermolecular forces are responsible for many of the properties of liquids such as vapor pressure, boiling point, viscosity, and surface tension.

The other topic in Lesson 12 is Solutions. These are an effective way to deliver quantities of dissolved chemicals in a mobile form. One common solution is saline solution which is salt dissolved in water. Saline solutions are used in the body for hydration and externally to rinse off contact lenses. Another common solution is liquid plant food, a water-based solution that contains iron, nitrogen, phosphorus, and potassium ions. The proportion of ions varies depending on the mineral needs of the targeted plant type. There are several useful ways to report the concentration of chemicals in solution.

Objectives for Lesson 12

After completing this lesson, you will be able to:

  • Explain how the interactions among water molecules give water its characteristic properties
  • Identify which intermolecular forces (dipole-dipole attraction, hydrogen bonding, and/or London dispersion) are acting between atoms or molecules 
  • Explain the relationship among vaporization, condensation, and vapor pressure 
  • Classify crystalline solids as Ionic, Atomic, or Molecular 
  • Explain how the atoms in crystalline solids are held together by inter particle forces 
  • Draw the process of an ionic substance dissolving in water 
  • Express the concentration of a solution 
  • Calculate the concentration of a solute in solution in mass percent 
  • Calculate the number of moles of solute present in a solution and express the number in units of molarity 
  • Dilute a solution of known concentration to a new concentration