Oh, contact-explosive chemicals, we love you. Nitrogen triiodide (NI3) is a black powder, produced when iodine crystals are added to a solution of concentrated ammonia in water. While the substance is wet, the water keeps it stable, but as the substance dries, it becomes wondrously unstable. It’s so touch-sensitive in fact, that a mosquito landing on it is enough to blow it up.
In their latest video, scientists at the Royal Institution (RI) turned to high-speed video to help explain why this molecule is such a touchy bastard. It all has to do with something called “bond strain:” if you think of a molecule like a dining-room table, there is an ideal way to arrange the chairs (the adjacent atoms) around the table itself (the central atom). The farther from this arrangement you get, the more uncomfortable your dinner guests will be. And when it comes to chemistry, cranky guests almost always go “boom.”
“In NI3, the iodine atoms are much bigger than the [central] nitrogen,” explains RI. And because of nitrogens electrons, which also take up space, all three iodine atoms are crammed onto one side. “They’re all squeezed together, and repelling each other, making it liable to fall apart.”
The explosion results in a stunning purple plume of iodine gas and colorless nitrogen gas, the building blocks of our original molecule. “The triiodide molecules are falling to pieces and recombining into a different arrangement,” says RI. “And it’s this recombination that releases all of the energy.” The atoms are basically dancing their way through one of those painful “snowball” songs from a middle-school soirée. As energy is released in the reaction, more and more NI3 molecules follow suit, breaking apart and recombining. The chain reaction races through the substance so fast, your brain can only process it as a single, mighty blast.
Want more NI3 in your life? Lucky for us, this isn’t RI’s first go at blowing the stuff up:
IMAGES: Royal Institution/Youtube