Nitrogen triiodide is an

inorganic compound An inorganic compound is typically a chemical compound that lacks carbon–hydrogen bonds⁠that is, a compound that is not an organic compound. The study of inorganic compounds is a subfield of chemistry known as ''inorganic chemistry''. Inorgan ...

with the formula N I₃. It is an extremely sensitive

contact explosive A contact explosive is a chemical substance that explodes violently when it is exposed to a relatively small amount of energy (e.g. friction, pressure, sound, light). Though different contact explosives have varying amounts of Sensitivity (explos ...

: small quantities explode with a loud, sharp snap when touched even lightly, releasing a purple cloud of

iodine Iodine is a chemical element; it has symbol I and atomic number 53. The heaviest of the stable halogens, it exists at standard conditions as a semi-lustrous, non-metallic solid that melts to form a deep violet liquid at , and boils to a vi ...

vapor; it can even be detonated by

alpha radiation Alpha decay or α-decay is a type of radioactive decay in which an atomic nucleus emits an alpha particle (helium nucleus). The parent nucleus transforms or "decays" into a daughter product, with a mass number that is reduced by four and an atom ...

. NI₃ has a complex structural chemistry that is difficult to study because of the instability of the derivatives.

Structure of NI₃ and its derivatives

Nitrogen triiodide was first characterized by

Raman spectroscopy Raman spectroscopy () (named after physicist C. V. Raman) is a Spectroscopy, spectroscopic technique typically used to determine vibrational modes of molecules, although rotational and other low-frequency modes of systems may also be observed. Ra ...

in 1990, when it was prepared by an ammonia-free route.

Boron nitride Boron nitride is a thermally and chemically resistant refractory compound of boron and nitrogen with the chemical formula B N. It exists in various crystalline forms that are isoelectronic to a similarly structured carbon lattice. The hexago ...

reacts with

iodine monofluoride Iodine monofluoride is an interhalogen compound of iodine and fluorine with formula IF. It is a chocolate-brown solid that decomposes at 0 °C, disproportionation, disproportionating to elemental iodine and iodine pentafluoride: :5 IF → 2 ...

trichlorofluoromethane Trichlorofluoromethane, also called freon-11, CFC-11, or R-11, is a chlorofluorocarbon (CFC). It is a colorless, faintly ethereal, and sweetish-smelling liquid that boils around room temperature. CFC-11 is a Class 1 ozone-depleting substance w ...

at −30 °C to produce pure NI₃ in low yield: :BN + 3 IF → NI₃ + BF₃ NI₃ is pyramidal (C_3v

molecular symmetry In chemistry, molecular symmetry describes the symmetry present in molecules and the classification of these molecules according to their symmetry. Molecular symmetry is a fundamental concept in chemistry, as it can be used to predict or explai ...

), as are the other nitrogen trihalides and

ammonia Ammonia is an inorganic chemical compound of nitrogen and hydrogen with the chemical formula, formula . A Binary compounds of hydrogen, stable binary hydride and the simplest pnictogen hydride, ammonia is a colourless gas with a distinctive pu ...

. The material that is usually called "nitrogen triiodide" is prepared by the reaction of iodine with

. When this reaction is conducted at low temperatures in anhydrous ammonia, the initial product is NI₃ · (NH₃)₅, but this material loses some ammonia upon warming to give the 1:1

adduct In chemistry, an adduct (; alternatively, a contraction of "addition product") is a product of a direct addition of two or more distinct molecules, resulting in a single reaction product containing all atoms of all components. The resultant is ...

NI₃ · NH₃. This adduct was first reported by

Bernard Courtois Bernard Courtois (), also spelled Barnard Courtois, (8 February 1777 – 27 September 1838) was a French chemist credited with first isolating iodine, making early photography possible. By 1811 the Napoleonic Wars had made the government-contro ...

in 1812, and its formula was finally determined in 1905 by

Oswald Silberrad Oswald J. Silberrad (1878 – 17 June 1960) was a British chemist who specialised in explosives, the related field of dye stuffs, and metallurgy. Life and works Silberrad was born at Buckhurst Hill in Essex and was the younger brother of th ...

. Its solid state structure consists of chains of -NI₂-I-NI₂-I-NI₂-I-. Ammonia molecules are situated between the chains. When kept cold in the dark and damp with ammonia, NI₃ · NH₃ is stable.

Decomposition and explosiveness

The instability of NI₃ and NI₃ · NH₃ can be attributed to the large

steric strain Van der Waals strain is strain resulting from Van der Waals repulsion when two substituents in a molecule approach each other with a distance less than the sum of their Van der Waals radii. Van der Waals strain is also called Van der Waals repul ...

caused by the three large iodine atoms being held in proximity to each other around the relatively tiny

nitrogen Nitrogen is a chemical element; it has Symbol (chemistry), symbol N and atomic number 7. Nitrogen is a Nonmetal (chemistry), nonmetal and the lightest member of pnictogen, group 15 of the periodic table, often called the Pnictogen, pnictogens. ...

atom. This results in a very low

activation energy In the Arrhenius model of reaction rates, activation energy is the minimum amount of energy that must be available to reactants for a chemical reaction to occur. The activation energy (''E''a) of a reaction is measured in kilojoules per mole (k ...

for its decomposition, a reaction made even more favorable due to the great stability of N₂. Nitrogen triiodide has no practical commercial value due to its extreme shock sensitivity, making it impossible to store, transport, and utilize for controlled explosions. Whereas pure

nitroglycerin Nitroglycerin (NG) (alternative spelling nitroglycerine), also known as trinitroglycerol (TNG), nitro, glyceryl trinitrate (GTN), or 1,2,3-trinitroxypropane, is a dense, colorless or pale yellow, oily, explosive liquid most commonly produced by ...

is powerful and also greatly shock-sensitive (although not nearly as much so as nitrogen triiodide, which can be set off with the touch of a feather), it was only due to

phlegmatizers A phlegmatizer is a compound that minimizes the explosive tendency of another compound or material. The term is derived from the word phlegmatic, meaning 'not easily excited'. Many chemical compounds that are potentially explosive have useful non- ...

that nitroglycerin's shock sensitivity was reduced and it became safer to handle and transport in the form of

dynamite Dynamite is an explosive made of nitroglycerin, sorbents (such as powdered shells or clay), and Stabilizer (chemistry), stabilizers. It was invented by the Swedish people, Swedish chemist and engineer Alfred Nobel in Geesthacht, Northern German ...

. The decomposition of NI₃ proceeds as follows to give nitrogen gas and iodine: :2 NI₃ (s) → N₂ (g) + 3 I₂ (g) (−290 kJ/mol) However, the dry material is a contact explosive, decomposing approximately as follows: : 8 NI₃ · NH₃ → 5 N₂ + 6 NH₄I + 9 I₂ Consistent with this equation, these explosions leave orange-to-purple stains of iodine, which can be removed with

sodium thiosulfate Sodium thiosulfate (sodium thiosulphate) is an inorganic compound with the formula . Typically it is available as the white or colorless pentahydrate (x = 5), which is a white solid that dissolves well in water. The compound is a reducing agent an ...

solution. An alternate method of stain removal is to simply allow the iodine time to sublime. Small amounts of nitrogen triiodide are sometimes synthesized as a demonstration to high school chemistry students or as an act of "chemical magic." To highlight the sensitivity of the compound, it is usually detonated by touching it with a feather, but even the slightest air current, laser light, or other movement can cause

detonation Detonation () is a type of combustion involving a supersonic exothermic front accelerating through a medium that eventually drives a shock front propagating directly in front of it. Detonations propagate supersonically through shock waves with ...

. Nitrogen triiodide is also notable for being the only known chemical explosive that detonates when exposed to

alpha particles Alpha particles, also called alpha rays or alpha radiation, consist of two protons and two neutrons bound together into a particle identical to a helium-4 nucleus. They are generally produced in the process of alpha decay but may also be produce ...

and

nuclear fission Nuclear fission is a reaction in which the nucleus of an atom splits into two or more smaller nuclei. The fission process often produces gamma photons, and releases a very large amount of energy even by the energetic standards of radioactiv ...

products.

References

External links

Nitrogen Tri-Iodide – explains why the compound is explosiveNitrogen Tri-Iodide Detonation on Youtube
{{Nitrogen compounds Inorganic amines Iodides Nitrogen halides Explosive chemicals

Structure of NI3 and its derivatives

Decomposition and explosiveness

References

External links

Structure of NI₃ and its derivatives