Stability of molecular hydrides
 

Hi all,

When you go down a gp from NH3 to PH3 to AsH3 the stability of the cmpds falls. Can anyone say why?

Also, why is ammonia much higher boiling than the others. Thanks.

The stability decreases with decreasing bond dissociation energy. Lower energy bonds split more easily.

NH₃ ~ 339 kJ/mol
PH₃ ~ 297 kJ/mol
AsH₃ ??? kJ/mol
SbH₃ ~ 240 kJ/mol

NH₃ has a much higher boiling point than the others because of hydrogen bonding. That's also why H₂O has a much higher boiling point than you'd expect.