Which compound has a higher boiling point and why?
a. PF3
b. PF5
PF5 is higher. When I was in school the answer was that the molar mass of PF5 is greater. The "more modern answer" is because of higher intermolecular forces. Frankly, I like the old answer better.
Thank you DrBob
To determine which compound has a higher boiling point between PF3 and PF5, we need to consider their molecular structures.
PF3: The chemical formula PF3 represents phosphorus trifluoride. It consists of one phosphorus atom bonded to three fluorine atoms.
PF5: The chemical formula PF5 represents phosphorus pentafluoride. It consists of one phosphorus atom bonded to five fluorine atoms.
The boiling point of a compound depends on the strength and type of intermolecular forces between its molecules. These intermolecular forces can include London dispersion forces, dipole-dipole interactions, and hydrogen bonding.
In this case, both PF3 and PF5 are nonpolar molecules. Nonpolar molecules generally experience weaker London dispersion forces compared to polar molecules or molecules with permanent dipoles.
Between PF3 and PF5, PF5 has a higher boiling point. This is because PF5 has more electrons and a larger molecular size, resulting in stronger London dispersion forces compared to PF3. The stronger intermolecular forces in PF5 require more energy to break the bonds and convert the substance from a liquid to a gas, leading to a higher boiling point compared to PF3.
To determine which compound, PF3 or PF5, has a higher boiling point, we need to examine their molecular structures and intermolecular forces.
PF3 is a molecule with a trigonal pyramidal shape. It consists of one phosphorus atom (P) and three fluorine atoms (F) bonded to it. The molecular shape and the presence of polar bonds make it a polar molecule. These polar bonds create a partial positive charge on the phosphorus atom and partial negative charges on the fluorine atoms.
On the other hand, PF5 is a molecule with a trigonal bipyramidal shape. It consists of one phosphorus atom (P) bonded to five fluorine atoms (F). Unlike PF3, PF5 is a nonpolar molecule. This is because the geometry of PF5 results in dipoles (polar bonds) that cancel each other out, leading to no overall molecular polarity.
When comparing boiling points, the strength of intermolecular forces is crucial. In general, polar molecules have stronger intermolecular forces than nonpolar molecules due to the presence of dipole-dipole interactions. Dipole-dipole interactions occur when the positive end of one polar molecule attracts the negative end of another polar molecule.
Because PF3 is a polar molecule, it will exhibit dipole-dipole interactions between its molecules. Consequently, these intermolecular forces will be stronger than the intermolecular forces present in nonpolar PF5 molecules.
Therefore, PF3 has a higher boiling point compared to PF5 due to the stronger dipole-dipole interactions resulting from its polarity.