Nitrogen is one of a handful of elements that have been suggested as alternatives to carbon as the basis of life elsewhere in the universe. Principally this is because it can form long chains at low temperatures with a liquid solvent such as ammonia (NH₃) or hydrogen cyanide (HCN). On the other hand, a major drawback of nitrogen as a backbone for large molecular structures is that the energy of the triple bond in N₂ is much greater than that for a single bond, so that nitrogen-nitrogen bonds tend to revert back to elemental nitrogen. Nitrogen can, however, form longer molecules with some other elements, including carbon, phosphorus, sulfur, and boron. Nitrogen can also form hydrides, such as hydrazine.