 Two things affect inter molecular forces: › Charge › Distance  Bigger distance equals LESS attraction!  More charge equals MORE attraction!  Coulomb’s Law › F ~ charge/distance 2 › Distance has more effect since it is squared.

 Bonds are permanent attractions, IMF’s are temporary

 Covalent › Sharing of electrons in permanent tug of war.  Ionic › Stealing electrons and then being attracted by opposite charges

 Ion Dipole  Hydrogen Bonding  Dipole-Dipole  London Dispersion forces

 Between an ion and a dipole! › Ion = permanently charged particle › Dipole = a polar molecule  Almost exclusively seen in aqueous solutions.

 Between two dipoles! › Dipoles are polar molecules that have no net charge, but the charge is distributed unequally. › Positive end of one attracts negative end of the other.

 ALL covalent compounds experience this force. › It is between the electrons in one atom and the nucleus of another atom. › More mass and/or more atoms means more dispersion forces.

› More mass doesn’t cause an increase in LDF! › More mass infers that there are more P and N, which MEANS there are more electrons. › It is an increase in the number of e- which causes a larger e- density which leads to a stronger temporary dipole. › You can use molar mass to figure it out since a larger molar mass implies a bigger density but you can't use the words molar mass in your justification in a Free Response Question

 Occurs in molecules in which hydrogen is having FON ! › The most electronegative atoms are F, O and N. With a hydrogen, there is excessive polarization. › This excessive polarization attracts the lone pair of electrons.

 Strongest:Ion-Dipole(very strong) Hydrogen Bonding (strong) Dipole-Dipole Dispersion Forces (very weak)

 More IMF’s or stronger IMF’s affect the following properties: › Boiling point › Melting Point › Viscosity (thickness) › Vapor Pressure › Surface tension

 Stronger IMF › Higher boiling point  Weaker IMF › Lower boiling point  Compare CS 2 to CO 2

Both are linear Both are nonpolar covalent Both have LDF CS 2 has stronger LDF – larger molecule means larger e- density

 Stronger IMF › Higher melting point  Weaker IMF › Lower melting point  Think of red rover…  Compare HBr to Cl 2

 Both are liner  HBr has LD, Dipole  Cl 2 has LD, nonpolar  HBr has stronger IMF – higher melting point

 Stronger IMF › Higher viscosity  Weaker IMF › Lower viscosity  More attached to each other, the hard to flow, like solids vs. liquids.  Compare CH 3 OCH 3 to CH 3 CH 2 OH

CH 3 OCH 3 LD, Dipole CH 3 CH 2 OH LD, HB Therefore CH 3 CH 2 OH has stronger IMF and a higher viscosity

 Stronger IMF › Lower vapor pressure  Weaker IMF › Higher vapor pressure  Again…think red rover.  Compare H 2 S to H 2 O 2

 H 2 S LD, Dipole  H 2 O 2 LD, HB  H 2 O 2 has stronger IMF therefore lower vapor pressure

 Resistance of a liquid to increase in its surface area  Stronger IMF › Higher surface tension  Weaker IMF › Lower surface tension  Compare H 2 CO to H 2 O

 H 2 CO LD, Dipole  H 2 O LD, HB  Hydrogen bonding is a stronger IMF than Dipole, therefore H 2 O has a stronger surface tension

 Stronger IMF › Higher boiling point › Higher melting point › Higher viscosity › Higher surface tension › Lower vapor pressure  Weaker IMF › Lower boiling point › Lower melting point › Lower viscosity › Lower surface tension › Higher vapor pressure