Lesson-4-Intermolecular-Forces24.pptx

What Holds Molecules Together? Intermolecular Forces of Attraction Called “Van der Waals Forces” They arise from weak “electrostatic attractions” between molecules.  Differentfrom “Intramolecular Forces” or “covalent bonds” that exist between atoms! Shows electrostat...

What Holds Molecules Together? Intermolecular Forces of Attraction Called “Van der Waals Forces” They arise from weak “electrostatic attractions” between molecules.  Differentfrom “Intramolecular Forces” or “covalent bonds” that exist between atoms! Shows electrostatic attractions between opposite charged areas on molecules  Forces Between Polar Molecules  Dipole-Dipole Attractions:  Occurs between polar molecules  Polar Molecule = “Permanent Dipole” asymmetrical molecule with polar bonds  Forces Between Polar Molecules  Hydrogen Bonding  Super strong Dipole-Dipole Attraction  Occurs when molecules have hydrogen atoms bonded to very small, highly electronegative atoms like F, O or N  Createsa very polar bond and an “extra polar” molecule.  Hydrogen Bonding between molecules results in unusually high MP/BP temps.  Water has hydrogen bonding between its molecules!  Ethanol can also form hydrogen bonds to itself and also with water that is why bartenders can make mixed drinks!  Remember:  Hydrogen Bonding is “FON”!!  Hydrogen bonds are responsible for ice floating on liquid water  Ice is ordered with open structure to optimize H-bonding.  Therefore, solid ice is less dense than liquid water.  Also it is responsible for water’s  Surface tension  How it beads Properties of Water: https://www.youtube.com/watch?v=3jwAG Wky98c Forces Between Nonpolar Molecules  Dispersion Forces (“weak force”)  Only attractive forces between nonpolar molecules and noble gas atoms.  Weakest of all intermolecular forces. * Exist in noble gases https://www.youtube.com/watch?v=kvTRL8uyM8o  Dispersion Forces have different strengths.  The more total electrons in a molecule, the greater the force can get.  Ex: Cl2 has 34 electrons (it’s a gas) Br2 has 70 electrons (it’s a liquid) I2 has 106 electrons (it’s a solid)  ACTIVITY # 2.4  Identify as dipole-dipole interaction, hydrogen bond or London force is present in each molecule interaction.  NH 3  HBr I 2  PBr 3  CO 2  Arrange the following according to decreasing IMFA.  CCl 4 H O 2  NaCl  ICl PROPERTIES  Why Do Ionics Dissolve in Water?  Molecule-Ion Attractions:  Attraction between polar solvent molecules and ions in an ionic crystal.  Allows polar solvent (like water) to “pull” the ions into solution, creating “hydrated” ions. Remember which side of water is negative! Ionic compounds are generally soluble in polar solvents like water. http://www.chem.iastate.edu/group/Greenbowe/sections/projectfolder/flashfiles/thermochem/solutionSalt.html What Effects do IMF Have? Melting and Boiling Point Temperature:  Stronger forces make it harder to separate molecules and undergo a phase change.  H-Bonding = highest MP/BP  Dipole-Dipole = middle MP/BP  London Dispersion Forces (only) = lowest MP/BP Solubility: solutes must form attractions to solvent to dissolve in it.  Polar solvents attract polar solutes  Nonpolar solutes only dissolve in nonpolar solvents.  Polar solvents attract ions  Application of IMFA  medical devices,  construction materials,  sports equipment,  and electrical devices.  Medical Devices  Medical implants and prosthetics, which are devices with tissues placed inside or on the surface of the body, should be carefully designed such that they will not cause infection, trigger allergic reactions, or fail to perform their functions. Some implants require the material to have high melting points so that it will not be damaged during the sterilization procedures done prior to its introduction into the body.  The solubility and reactivity properties of an implant depend on its application as well. Implants are usually designed to be insoluble and unreactive to the cell components and body fluids, particularly those that surround them. Some metal implants are produced as alloys to provide strength and better compatibility with the biological system.  Other materials used for medical implants, such as silicone, have soft, rubber-like, or jelly properties. The material used in these implants may be held together by van der Waals forces, hydrogen bonds, or covalent bonds. Some form permanent covalent networks, while others are only weakly held to make them more adaptive to certain temperatures. Self-check Test/ Reinforcement 2.2 Search about the application of IMFA in Construction materials Sports Equipment Electronic devices