Homework Problem 3F.19

[Talia Dini - 3I]

Hi, could someone please explain to me how I should solve this problem?

3F.19 Account for the following observations in terms of the type and strength of intermolecular forces. (a) The melting point of solid xenon is -112 C and that of solid argon is -189 C. (b) The vapor pressure of diethyl ether (C2H5OC2H5) is greater than that of water. (c) The boiling point of pentane, CH3(CH2)3CH3, is 36.1 C, whereas that of 2,2-dimethylpropane (also known as neopentane), C(CH3)4, is 9.5 C.

[Andreas Krumbein 1L]

a) xenon is larger than argon, and so it has stronger dispersion forces, and the melting point is higher. b) diethyl ether is nonpolar so it has weak intermolecular forces and a higher vapor pressure than water, which has hydrogen bonding and thus strong intermolecular forces. c) pentane's shape is longer and is thus more effected by LDF forces than neopentane, which is more spherical in shape by comparison.

[Samudrala_Vaishnavi 3A]

a.) Xenon is larger than Argon in terms of the atomic radius so it's bound to have more LDF forces since a bigger electron cloud is easy to be distorted b.) There is more of a rod-like structure for diethyl along with its hydrogen bonds so it has more extensive LDF forces as well. C.) Again, the rod-like structure of pentane allows for more LDF forces.

[Rachel Jiang 3H]

a) Xenon is a larger larger in atomic radius than argon, which means that it has a larger electron cloud that can be distorted (more polarizable), so xenon molecules will have stronger dispersion forces between them than argon. Stronger the IMFs, higher the melting/boiling points.

b) Diethyl ether is nonpolar, which means that it only has dispersion forces. Water is polar and it has dispersion forces, dipole-dipole interactions, and hydrogen bonding. The IMFs between water molecules are stronger than that between diethyl ether molecules. Therefore, diethyl ether, the liquid with weaker IMFs, evaporates more easily and has a higher vapor pressure.

c) Pentane and 2,2-dimethylpropane has the same molecular formula. Pentane is rod-shaped and 2,2-dimethylpropane is spherical-shaped. Instantaneous dipoles in two nearby rod-shaped molecules are closer and stronger than those in two nearby spherical molecules. Thus, pentane has stronger IMFs and a higher boiling point.

Hope this helps!

[Charlotte Adams 1A]

Just curious, did this question show the lewis structure of pentane and diethyl ether. I don't know if I would be able to tell which is more rod-shaped just based off the formulas.

Thanks!