CHEM 1312H 1nd Edition Exam 1 Study Guide Lectures 1 8 Lectures 1 and 2 1 5 and 1 7 there exists intermolecular forces between gases liquids and solids o ionic forces ion ion Coloumb s Law states that there is an attraction proportional to the product of the distance between the centers of the two atoms o intermolecular no charges a Dipole Dipole dip dip between polar covalent molecules or molecules that have a permanent dipole moment b Hydrogen Bonding special type of dip dip molecules contain one of the highly electronegative atoms Fluorine Oxygen or Nitrogen FON c London Dispersion Forces LDFs attractions between atoms or uncharged non polar molecules such as CH4 the farther you move down a period the bigger the electron clouds get increased polarizability the squishability of the electron cloud easier for LDFs to act because dipole moments come about easier when electrons are easier to snatch away heavier molecules increased molecular weight more LDFs always present as a force o intramolecular forces are generally stronger these forces include ionic covalent and metallic forces to be covered later Lecture 2 1 7 and associated readings PROPERTIES Viscosity resistance of a liquid to flow o depends on the attractive forces between molecules o for related compounds such as hydrocarbons viscosity increases with molecular weight o for any given substance viscosity decreases with increasing temperature Surface tension imbalance of IMFs at the surface leads the molecules there to experience a net inward downward pull this reduces the surface area and makes them pack closely together Capillary action the rise of liquid up very narrow tubes o binding of similar molecules is called cohesive forces PHASE CHANGES o every phase change also has an energy change transfer associated with it o melting is also called fusion the increased freedom of motion of the particles requires energy measured by the heat of fusion Hfus gas to liquid condensation liquid to gas vaporization liquid to solid freezing solid to liquid melting fusion solid to gas sublimation gas to solid deposition heat of vaporization Hvap is the energy required to turn liquid to gas Hvap is usually greater than Hfus for a substance because the energy that is needed to completely mobilize all participles is greater HEATING CURVES o enthalpy changes can be calculated from heating curves o heat in J used to calculate the slope y parts of the heating curve so A B and C D q mass in grams specific heat T heat energy used to calculate flat parts of curve so B C and D E q mass in grams either Hfus or Hvap CRITICAL TEMPERATURE AND PRESSURE o critical temperature the highest temperature at which a distinct liquid phase can exist o critical pressure the pressure required to bring about liquefaction at the critical temperature VAPOR PRESSURE o the pressure exerted by a vapor o dynamic equilibrium condition in which two opposing processes occur simultaneously at equal rates o liquids that evaporate readily are volatile Lecture 3 1 9 Liquid crystals hybrids between solids and liquids so that there is still some movement within the crystal among particles but there is also enough structure so as to remain a solid o a normal liquid o b nematic liquid crystal refer to Lecture 3 for illustrations o c smectic A liquid crystal refer to Lecture 3 for illustrations o d smectic C liquid crystal refer to Lecture 3 for illustrations o molecules align along the long axis to maximize IMFs o pitch distance required for the top layer of molecules in a cholesteric structure to be replicated after a certain number of rotations refer to Lecture 3 for illustrations if the pitch is larger you re diffracting longer wavelengths of light and vice versa red lights longer pitches blue lights shorter pitches as you change the temperature you also change the pitch distance heat the liquid pitch gets smaller turns more blue cool the liquid pitch gets longer turns more red to make a liquid crystal you want long rod like rigid molecules you also want strong bonds attractions like IMFs but not too strong of attractions so no ionic charges that would completely discourage movement in between molecules Lecture 4 1 12 SOLIDS o amorphous solids no long range order structure is similar to liquid s but ions molecules atoms don t have freedom of motion ex glass rubber o crystalline solids 3D order atoms are arranged in an orderly repeating pattern o unit cell smallest repeating unit of a crystal building blocks o crystal lattice the geometrical pattern of points on which the unit cells are arranged the building OVERVIEW OF THE CLASSES OF SOLIDS o ionic solids ion ion forces composed of cations and anions held together by mutual electrostatic attractions between cations and anions ex NaCl KBr MgO high melting points and boiling points typically brittle when a hammer hits an ionic solid and disrupts the structure the molecular layers shift laterally and cations with cations and anions with anions come in contact with each other upon contact they immediately repel which results in the brittle solid breaking and shattering many dissolve in water o molecular solids LDF dip dip hyodrogen bonding composed of molecules held together by IMFs tend to be soft and have low boiling and melting points ex ice composed of H2O solid CO2 low melting and boiling points softer o covalent network solids covalent bonding atoms that are bonded to its neighbor s by strong covalent bonds ex diamond pure carbon graphite SiC high boiling and melting points typically hard typically insoluble and very stable o metallic solids metallic bonding to be defined held together by collectively shared valence electrons this is what allows it to conduct electricity high melting points and boiling points malleable ductile good electrical conductors Lecture 5 1 14 and associated readings 3D STRUCTURES o primitive cubic lattice atoms are at all the corners 1 atom total unit cell o body centered cubic lattice lattice points at all 8 corners of the unit cell along with one at the center of the unit cells 2 atoms total unit cell o face centered all 8 corners along with at all 6 faces 6 atoms unit cell METALLIC SOLIDS o consist entirely of metal atoms o bonding is too strong to be from dispersion but there aren t enough valence electrons to form covalent bonds valence electrons are delocalized through the solid aka they are not associated with specific atoms or bonds but are spread throughout the solid o basically just an