Nitrogen – Nature’s Explosive Building Blocks

An animation showing the violent explosion of a nitrogen-filled balloon.“Lifeless”

One of the all-time most interesting elements in the Periodic Table, nitrogen is a colourless, odourless, inert diatomic gas that makes up to 78% of the Earth’s atmosphere.  We breathe it everyday, although an atmosphere of pure nitrogen is nefarious to animal and human life.  It is vital to life and plants simply strive on it.  Nitrogen compounds are explosive, and nations have gone to war over it.  It can feed… or kill.

Nitrogen is a common element in the Universe – the seventh for total abundance in the Solar System and Milky Way.  It was isolated as a separable component from air, by Scottish physician Daniel Rutherford in 1772.

 

Phlogisticated Air

The element was studied around the same time by Swedish chemist Carl Wilhelm Scheele, and British Henry Cavendish and Joseph Priestley who designated it as phlogisticated air.

Molecular nitrogen N2 binds two nitrogen atoms into a highly stable molecule, held together by a very strong triple covalent bond – the strongest in Nature – in which the atoms share a total of six electrons.  The reverse side to nitrogen’s incredibly stable bond is the element’s ability to form compounds that are extremely volatile.

Nitrogen compounds were known to alchemists from the Middle Ages.  They were familiar with nitric acid as aqua fortis (strong water) and aqua regia (royal water) – its mixture with hydrochloric acid, capable of dissolving gold.

The earliest military, industrial, and agricultural applications of nitrogen compounds used saltpetre – sodium nitrate NaNO3 or potassium nitrate KNO3 – most notably in gunpowder.

 

Nobel’s Heritage

Nitrogen is remarkable for the range of explosively unstable compounds it can produce.  In 1910, English physicist Lord Rayleigh discovered that an electrical discharge in nitrogen gas produced “active nitrogen” – a monatomic allotrope of nitrogen.  The whirling cloud of brilliant yellow light produced by his apparatus reacted with quicksilver to produce explosive mercury nitride Hg3N2.

A diagram showing the triple-bond of a nitrogen molecule.
Triple Covalent Bond of Nitrogen Molecule

Almost all explosives exploit the tendency of nitrogen to form a triple bond.  Nitroglycerin and TNT (Trinitrotoluene) are compounds of nitrogen, oxygen, hydrogen and carbon.  One of gunpowder’s main ingredients is potassium nitrate.

Nitrogen Tri-iodide NI3 is made of nitrogen and purple iodine.  Nitrogen triiodide is an extremely sensitive contact explosive, so sensitive it can be detonated by the slightest touch, even by alpha radiation.  Small quantities explode with a loud, sharp snap, releasing a purple cloud of iodine vapour…An animation showing the explosion of a nitrogen compound triggered by a small tap.

These compounds hold together by relatively weak bonds.  When the bonds are broken, nitrogen atoms form strong triple bonds with one another, while enormous amounts of energy are released.  As the solid is converted into a gas, the element expands almost 1,000 times.

In nature, nitrogen is converted into biologically useful compounds by lightning, and some living organisms…

 

Exploding with Life

The helical model of DNA, comprising the chemical elements: hydrogen, oxygen, nitrogen, carbon and phophorous.
The Chemical Elements of DNA

Nitrogen plays a fundamental role in sustaining life on Earth.  Nitrogen compounds are basic building blocks in animal biology, including the manufacture of proteins and nucleic acids.

DNA and RNA – the complex instructions for life – are molecules that include nitrogen

Amino acids – the agents of the biological world – are the basic units that make up proteins.  They are the catalysts that supports chemical reactions inside living cells, moving molecules and ions around.  They separate DNA strands and replicate the genome code.

Overall, the human body contains about 3% by mass of nitrogen.  It is the fourth most abundant element in the body after oxygen, carbon, and hydrogen.  This figure is as high as 15% in hair, due to the amino acid composition of keratin – the protein which is the main structural component of hair, nails and antlers.

A photograph showing the nitrogen-fixing nodules on a soybean plant rhizome.
The cells of nodules on the roots of this soybean plant (seen here) and other legumes contain nitrogen-fixing bacteria known as rhizobia.  Source: biology-forums.com

Plant life needs nitrogen – an essential fertiliser.  Plants are able to assimilate nitrogen directly in the form of nitrates that may be present in soil from natural mineral deposits, artificial fertilisers, animal waste or organic decay.  Surprisingly, plants make use of the very reactivity of nitrogen that gives explosives their main property.

In particular, rhizobium bacteria have become experts at using the metal atoms in their cell matrix to attack atmospheric nitrogen and perform the extraordinary chemical trick of breaking the triple bond by bombarding them with a mixture of protons and electrons.

 

The living world depends on the nitrogen fixation process.

 

The balanced equation of Nitrogen chemical fixation: N2 + 8H+ + 8e- gives 2NH3 + H2.
The Balanced Equation for the Nitrogen Fixation Chemical Reaction

The rhizobia process atmospheric nitrogen N2 and combine it with hydrogen H to form ammonia NH3 which plants use.  Plants and legumes nurture the bacteria in nodules attached to their roots.  These plants secrete sugars that feed the bacteria, while in turn the bacteria supply the roots with a constant supply of nitrogen.  When the plants die, nitrogen returns to the soil.

The relationship is symbiotic, with benefits to both plant and bacteria.  The rhizobia fix atmospheric nitrogen into ammonia and the plant provides organic acids as a food source to the bacteria.

 

Give Peas a Chance…

Over 8,000 years ago, the first farmers learned how useful this green manure could be.  Legumes are excellent natural soil fertilisers.  Growing them in rotation with other crops and cereals helps the soil remain nitrogen-rich, while producing protein-high nourishing pulses, including peas, soya beans or chick peas.

However, there is a limit to how much nitrogen can be extracted from the air and delivered to the soils using crop rotation.  With European and American populations rapidly expanding in the 19th Century, the World was getting hungry for fertiliser.A 19th century etching of one of the guano-mining Chincha Islands, off the southwest coast of Peru in South America.

From the 1840s to 1870s, Peru enjoyed an economic boom during the “Guano Age”.  Guano (bird droppings) was a valuable fertiliser, rich in nitrogen and phosphate, and the Chincha Islands were home to a long established colony of seabirds.  With populations growing, the value of the islands increased.  In 1864, Spain and Peru went to war over them. 

A photograph showing the open-cast mining of nitrates in the Atacama desert of Chile, in South America.
Nitrate Mining, Atacama Desert, Chile

When the guano ran out, it was replaced by mined nitrate, again largely controlled by Peru.  However, in The War of the Pacific (1879-1883), Chile fought Bolivia and Peru for control of the nitrate mines in the Atacama Desert region.  Chile won, taking control of nitrate production and a significant part of the World’s food production.  Nitrate was the oil of its day and a huge source of wealth.

 

The Haber-Bosch Process

Nitrogen is an industrial gas produced by the fractional distillation of liquid air.  Commercial nitrogen is often a by-product of air processing for industrial concentration of oxygen for steel-making and other purposes.

The Haber–Bosch process, is an artificial nitrogen fixation process and the main industrial procedure for the production of ammonia today.  Under high temperature and very high pressure, hydrogen and nitrogen (from thin air) are combined to produce ammonia.

 

A diagram explaining the Haber-Bosch ammonia production process.

 

The Haber-Bosch Ammonia Process directly combines nitrogen from the air with hydrogen under extremely high pressures and moderately high temperatures.  A catalyst made mostly from iron enables the reaction to be carried out at a lower temperature than would otherwise be practicable, while the removal of ammonia from the batch, as soon as it is formed, ensures that an equilibrium favouring product formation is maintained.

The lower the temperature and the higher the pressure used, the greater the proportion of ammonia yielded in the mixture.  For commercial production, the reaction is carried out at pressures ranging from 200 to 400 atmospheres and at temperatures ranging from 400° to 650° C (750° to 1200° F).  The Haber-Bosch process is the most economical for the fixation of nitrogen and with modifications continues in use as one of the basic processes of the chemical industry in the World.

 

Commercial production started in 1913.  Within a few decades, the super-exponential effect on the world’s population became obvious.

A century after its invention, the process is still applied all over the world to produce over 500 million tons of artificial fertilizer per year.

 

1% of the World’s energy supply is used in the Haber-Bosch process.

 

In 2004, the process sustained roughly 2 out of 5 people on the planet.  As of 2015, it sustains nearly 1 out of 2.  Soon, it will sustain 2 people out of 3 on Earth.

 

A graph showing the massive growth in World population since the invention of the Haber-Bosch process.
Historical Estimates of World Population Source: US Census Bureau

Good or Bad?

No other invention of the past 200 years compares to it in terms of the impact the Haber-Bosch process has had at the surface of our planet.

Billions of people would never have existed without it.  Half of global food production now relies on synthetic nitrogen fertilisers.

And yet, the incredible yields synthetic fertilisers deliver explain why obesity has replaced hunger as the rich World’s biggest nutritional challenge.

Besides, all the extra nitrogen mankind is extracting from the air has to end up somewhere. 

 

Eutrophication

Soluble nitrate is an important limiting factor to bacterial growth in ocean waters.  Some nitrogen passes through our bodies and that of animals, and is flushed away in sewage.  Still more nitrogen is washed straight off the fields into river mouths by heavy rain, or leaches into groundwater.

A NASA satellite photograph showing algal bloom off the coast of Iceland, in the North Atlantic ocean.
Algal bloom off Iceland, 2010  Source: NASA

This causes ecosystems to become overloaded with nitrogen, a process known as “eutrophication”.  What happens is great blooms of algae, and then bacteria, feed on the surplus nitrogen.  In the process, they suck all the oxygen from the water, killing fish and other organisms.

According to Lewis & Maslin in ‘Defining the Anthropocene’, Nature 2015, the Haber-Bosch process has “altered the global nitrogen cycle so fundamentally that the nearest suggested geological comparison refers to events about 2.5 billion years ago“.

Our dependence on fertilizer will only increase as the global count moves towards ten billion people or so.

Of course, that’s only part one of the incredible nitrogen story…