Why does I2 have a higher boiling point than F2? And why does NH3 have a higher boiling point than PH3?

Answer 1

NH3 has a higher b.p. than PH3 because of hydrogen bonding. The "old" answer for the higher b.p. I2 over F2 was higher molar mass; the "new" answer is increased "intermolecular" (London) forces.