Samantha F. answered • 10/26/20
Math and Science Support
Hi Robert, I am a high school and college level chemistry tutor. I hope you find my answer helpful!
You have pure samples of the following liquids: chlorine (Cl2) and hydrogen chloride (HCl).
(a) Identify the strongest intermolecular force experienced by the particles in each of these substances.
There are four types of intermolecular forces:
1) Ion-dipole interactions - Attraction between an ion and the opposite partial charge on a polar molecule.
2) Dipole-dipole interactions - Attraction between opposite partial charges on polar molecules.
3) Hydrogen Bonding - A type of dipole-dipole interaction between molecules with H-O, H-N, and H-F bonds.
4) London Dispersion Forces - A temporary, uneven distribution of electrons in the molecule induces a dipole that allows the partially charged sides to interact with nearby molecules. This is the weakest of the intermolecular forces. It is the only intermolecular force between nonpolar molecules.
Since Cl2 is an uncharged, nonpolar molecule, it is only acted upon by London Dispersion Forces.
HCl is an uncharged, polar molecule that does not contain bonds H-O, H-N, or H-F. It most strongly experiences dipole-dipole interactions.
(b) On your own sheet of paper, draw the Lewis structures* for two separate HCl molecules, and appropriately label the partial positive and partial negative end of each molecule. Display the formation of the attractive force between the molecules of HCl as the sample enters the liquid phase.
Key: partial positive (δ+), partial negative (δ-), formation of attractive force between molecules (• • •).
δ- δ+ • • • δ- δ+
Cl—H Cl—H
*Include two electron dots on the top, bottom, and left-hand side of each Cl atom for a complete Lewis dot structure.
(c) Which liquid do you expect to have the highest boiling point? Explain.
Temperature is the measure of energy in a system. Liquids with stronger intermolecular forces require more energy, (aka, a higher temperature), to break free of these forces keeping molecules in the liquid phase and escape into the gas phase. HCl's dipole-dipole interactions are stronger intermolecular forces than Cl2's London Dispersion forces. Therefore, it will take more energy/a higher temperature for HCl to transition to the gas phase than Cl2, and HCl will have the highest boiling point.
(d) Both liquids are heated to high enough temperatures to enter the gas phase. Which gas do you expect to better demonstrate ideal behavior? Explain.
Ideal gases are made of theoretical, massless particles that do not attract or repel one another. No gas is perfectly ideal, but some gases act more closely to an ideal gas than others. For example, the group 8A noble gases have a full valence shell, and therefore no incentive to bond or react with other atoms or molecules. This lack of reactivity is what gives them properties similar to those of ideal gases. As a polar molecule we learned in part (a) that HCl has stronger intermolecular forces than Cl2 because it is a polar molecule and Cl2 is not. These stronger forces will make HCl more reactive than Cl2. Since ideal gases are nonreactive, Cl2 would better demonstrate ideal behavior than HCl.
