Secondly, the ability to form more than one hydride falls off as
we go across a period. Thus, in Period 1. boron and carbon both
form whole families of hydrides, nitrogen forms three (ammonia.
NH3; hydrazine. N2H4; hydrazoic acid. N3H). oxygen two (H2O.
H2O2) and fluorine one (HF). Again, as we descend a group, the
energetic stability of the hydrides decreases—indeed, many hydrides
are endothermic. and need indirect methods to supply the necessary
energy for their preparation. In Group IV, methane is exothermic,