WS 3.2 IMF key 1.
SO2 dipole-­‐dipole H2O H-­‐bonding CH2Cl2 dipole-­‐dipole SCO dipole-­‐dipole PCl3 dipole-­‐dipole SO3 London dispersion 2.
a. Cl2 Lewis structure shows that this is a nonpolar b. CO Lewis structure shows that this is a polar molecule, therefore London dispersion forces are the only IMF molecule, therefore dipole-­‐dipole forces are the only IMF c. SO2 dipole-­‐dipole d. CH2Cl2 dipole-­‐dipole e. HF Lewis structure shows that this is a polar molecule specifically hydrogen bonding. g. CH3-­‐O-­‐CH3 dipole-­‐dipole 3.
a)
Boiling points of substances are related to their strength of intermolecular forces of attraction. The stronger the IMF the higher the boiling point. propane (LDF) dimethyl ether (dipole-­‐dipole) ethanol (H-­‐bonding) b) All three molecules are nonpolar molecules, they do not have any net dipoles on the molecules, therefore they all attract via LDF’s. The strength of the LDF is based upon the molar mass of the molecule. The greater the mass the more electrons the molecule has and therefore it is more polarizable. Increasing order for B.P. is: Cl2, Br2, I2. 4.
a)
B.P. is directly related to strength of IMF. SO2 is higher than CO2 because when you view the lewis structures you can see that SO2 is a polar molecule which uses dipole-­‐dipole forces of attraction and CO2 is nonpolar which uses London dispersion forces. b) CH3OH is a polar molecule attracting via hydrogen bonding, so it’s B.P. is higher than CH3OCH3 which is also polar, but utilizes dipole-­‐dipole forces of attraction. Once again if you look at the lewis structures you can see this. 5.
Propanol has a higher B.P. due to stronger IMF’s of attraction because it attracts with hydrogen bonding the other molecule attracts via dipole-­‐dipole forces. 6.
Again draw lewis structures and look at the IMF’s of attraction. Ne is a nonpolar molecule attracting via London dispersion forces. CH4 is nonpolar attracting via LDF’s. C2H4 is nonpolar attracting via LDF’s. The first three all use LDF, the ranking is based on increasing molar mass, more electrons, more easily polarized. H3COCH3 is a polar molecule attracting via dipole-­‐
dipole IMF’s. 7.
a) c) no H-­‐bonding possible e) g) i) b) d) f) h) j) No H-­‐bonding possible. 8.
a)
Not possible because the H atom on the top structure must bonded to an O, N, or F atom in order for the electronegativity difference to be high enough to create a H-­‐bond. b) Not possible because the H atom on the left structure must bonded to an O, N, or F atom in order for the electronegativity difference to be high enough to create a H-­‐bond. c) Yes the H atom in the water molecule is bonded to an O, therefore the electronegativity difference creates a H-­‐
bond with the other molecules’ O atom. d) Not possible because the H atom on the left structure must bonded to an O, N, or F atom in order for the electronegativity difference to be high enough to create a H-­‐bond. 9.
a)
False. Hydrogen bonding is only between molecules, not within the same molecule. • Hydrogen bonding can occur between molecules that have a hydrogen bonded to N, O, or F. b) False. Hydrogen doesn’t have a lone pair, also Hydrogen bonding is an electromagnetic force of attraction between polar molecules. • Hydrogen bonding can occur between the negatively charged region surrounding the oxygen and the positively charged region of a hydrogen atom. c) False. Ionic bonding is stronger • Hydrogen bonding is a weaker IMF of attraction than an ionic bond. 10. 11.