Explain why the boiling point of PH3 is lower than the boiling point of AsH3

AsH3 is a larger molecule than PH₃ as As is lower down the periodic table, so has a higher atomic number so more electrons. Therefore AsH₃ has more electrons than PH₃ meaning that the instantaneous dipole produced by AsH₃ is greater. Therefore the induced dipoles on neighbouring molecules are greater, so the London forces are stronger than in PH₃. Therefore more energy is required to overcome the intermolecular forces between the molecules.