Intermolecular and Ionic Forces Laboratory task.

Intermolecular and Ionic Forces
Introduction: Molecules are attracted to each other in the liquid and solid states by intermolecular, or
attractive, forces. These are the attractions that must be overcome when a liquid becomes a gas (vaporization)
or a solid becomes a gas (sublimation). In the gas phase molecules are much farther apart and, therefore, do
not interact as strongly as they do in the liquid (condensed) phase. Thus, the energy required to boil or
vaporize a pure substance is a measure of the strength of the intermolecular forces in that substance. In
general, intermolecular forces are much weaker than the ionic and covalent bonds that hold together the
atoms and ions in a compound. For example, about 40 kJ of energy are required to vaporize 18 grams of
water molecules—i.e., completely convert 18 grams of water to water vapor or steam. In contrast, 930 kJ of
energy is required to break all of the O-H covalent bonds in the same amount of water!
Alkanes (molecules with C and H atoms), alcohols (molecules with C, H, and O atoms), and ketones (C
double-bonded to O and single-bonded to two other C’s) will be the three types of organic compounds
compared in this lab. The alkane used in this activity is pentane, CH3CH2CH2CH2CH3. Alcohols are
similar to alkanes except one carbon in the chain is bonded to a hydroxyl (-OH) group (see the figures
shown below). The alcohol used in this activity is ethanol, CH3 CH2OH. The ketone used in this lab is
acetone (the primary ingredient in fingernail polish remover), CH3COCH3.