We are being asked to specify which among PF5, AsF5, and SbF5 would exist as solid, liquid and gas at a given temperature.
Recall that there are several types of intermolecular forces (IMF):
1. Ion-dipole interaction – occurs between an ion and a polar covalent compound; strongest IMF
2. Hydrogen bonding – occurs in compounds where hydrogen is directly connected to an electronegative element such as N, O, or F; 2nd strongest IMF
3. Dipole-dipole interaction – occurs between two polar covalent compounds; 3rd strongest IMF
4. Dispersion forces – occurs in all compounds and is the primary IMF exhibited by nonpolar compounds; weakest IMF
Compounds with strong intermolecular forces are most likely to exist as solids and compounds with weak intermolecular forces are most likely to exist as gases.
The later members of group VB form pentafluorides: PF5, AsF5, and SbF5. At a given temperature, one of these is a solid, one a liquid and one a gas. Specify which is which.
A. PF5 is a gas; AsF5 is a liquid; and SbF5 is a solid
B. PF5 is a liquid; AsF5 is a solid; and SbF5 is a gas
C. PF5 is a solid; AsF5 is a gas; and SbF5 is a liquid
D. PF5 is a solid; AsF5 is a liquid; and SbF5 is a gas
E. PF5 is a liquid; AsF5 is a gas; and SbF5 is a solid