Chemistry in the Military!: Fulminated Mercury

If you don't watch Breaking Bad, you're missing out! Look, even Peter Griffin says that it's the best show on TV. Breaking Bad is an amazing series that follows Walter White, a highschool chemistry teacher who makes and sells methamphetamine in order to secure his family's financial future before he dies. In one episode, Walter White negotiates a deal with a crazy and hostile drug lord. Walter throws a piece of Fulminated Mercury onto the floor, resulting in a huge explosion. You can watch the video by clicking on the hyperlink. In the show, however, the explosion is exaggerated, but the concept and the chemistry are the same.

Mercury(II) fulminate molecule

Mercury (II) fulminate comprises two fulminate ions (CNO^-) bonded to a central mercury atom. Due to the instability of the fulminate ion, fulminate is very sensitive. This volatile ion's name is derived from the Latin word "fulmen" which means lightning. Fulminate's instability can be attributed to two primary reasons. If you take a look at the fulminate ion in the picture below, you will see that there is a triple bond between the nitrogen and carbon atoms, and a single bond between the nitrogen and oxygen atoms. The triple bond is very stable, but the single bond is very unstable. Therefore, that single bond will immediately break in most reactions, and nitrogen will most likely bond with other nitrogen atoms, forming nitrogen gas. The second factor that contributes to fulminate's instability is the charges on each of its atoms. If were to draw out all of the resonance structures for fulminate, you'd notice that in every case the carbon atom is negatively charged, either with a 1^-, 2^-, or 3^-. This negatively charged carbon atom is highly unstable, which ultimately affects the stability of the fulminate ion itself.

Mercury fulminate can be easily prepared by dissolving mercury in nitric acid and then adding ethanol to the solution. It was first prepared by British chemist Edward Charled Howard in 1800. With a sufficient amount of

pressure or friction, mercury fulminate will explosively decompose into nitrogen, carbon monoxide, and mercury metal. This versatile property of mercury fulminate has been exploited since the 1800s. Alfred Nobel filled blasting caps with mercury fulminate for detonating dynamite. This relatively safe new detonator was what allowed for the huge success of dynamite. In Germany alone, the annual production of mercury fulminate in the early 20th century reached about 100,000 kg.

Mercury fulminate crystals are orthorhombic. As mentioned before, two fulminate ions are bonded to a central mercury atom. The molecule is almost linear, but not quite. There is still much research to be done on the molecule, as its structure was only determined and confirmed in 2007, over 200 years after its discovery. The measured positions and bond lengths confirm a molecular structure of O−N≡C−Hg−C≡N−O. In Breaking Bad, the mercury fulminate is shown as 1 inch long crystals, but in reality, the compound will be a powdery substance or very thin and needle-like.