# Which is the least stable trihalide of nitrogen?

Which is the least stable trihalide of nitrogen and why?
I have two conflicting theories, one is that fluorine-fluorine electron repulsion will make $\ce{NF3}$ least stable and another is steric reasons of iodine which give $\ce{NI3}$ as the answer.

Which is correct?

Nitrogen triiodide $\ce{NI3}$ is an extremely sensitive explosive that explodes with the slightest touch when dry.
Nitrogen trifluoride $\ce{NF3}$ is so stable that it is a greenhouse gas global warming concern, with lifetime in the atmosphere of hundreds of years.
$\ce{NI3}$ is unstable due to steric strain as you are saying.
• I agree with Dave's answer, but would add that iodoform ($\ce{CHI3}$) is stable. I suspect that $\ce{NI3}$ is unstable due to sterics and an extremely exothermic pathway leading to the formation of the very stable $\ce{N#N}$ triple bond. A similar decomposition pathway does not exist for iodoform, hence its relative stability. – ron Feb 17 '15 at 21:29