p Block Elements Part 1

The case of formation and stability of hydrides decreases rapidly from NH3 to BiH3. This is evident from their dissociation temperature which decreases from NH3 to BH3. As we go down the group the size of central atom increases and thus metal-hydrogen bond becomes weaker due to decreased overlap between the large central atom and small hydrogen atom.
‌

NH3

(‌ most stable ‌)

>PH3>AsH3>SbH3‌

>BiH3

(‌ least stable ‌)