# Are molecules with bond orders less than one stable?

Are molecules with bond orders less than one stable? My professor commented that they were "barely alive" but what does he mean, scientifically?

I know that molecules with fractional bond orders greater than one can exist - i.e. nitrogen oxide has a bond order of 2.5 (through MO calculations) and it exists just fine.

So are molecules with fractional bond orders below one just very unstable?

• Xenon Fluoride and the most noble gas compounds would have a bond order of 1/2 and by themselves they are quite stable though they are some of strongest organising agents. – user2617804 May 18 '14 at 10:35
• @user2617804 You may need to copy, delete and repost an edited version of this comment. Somehow "oxidizing" became "organising". – Oscar Lanzi May 6 '18 at 0:41

Molecules possessing a bond of order below 1 can be perfectly stable, in the sense that their resulting molecular structure lies in an energetic potential well. Strictly speaking it is enough that at $T=\pu{0 K}$ and in the absence of any interactions with matter or fields, the molecule will not spontaneously disassemble. However, there is no need to go quite so far to protect such a molecule from decomposing; there are examples of species which are chemically important in regular laboratory conditions.
All other things being equal, it is true that species with bond orders below 1 are relatively unstable. This is mainly because the fractional bond is comparatively weak (requiring comparatively little activation energy to break, i.e. a smaller $E_\mathrm{a}$), and because in most cases the molecule can react with other substances in such a way as to form products with all covalent bonds of bond order 1 or higher (increasing the exergonicity of most reactions, i.e. a more negative $\Delta_\mathrm{r}G$).