The noble gases represent a key group of the inorganic chemicals sector, which in turn, forms the basis of the commodity chemicals market and the manufacturing industries. Tony Wheatley explains.
Inorganic chemicals may be defined as a broad class of substances, including those that do not include carbon and its derivatives as their principal element, but also including carbides, carbonates, cyanides, cyanates, thyocyanates and carbon disulfide.
Inorganic molecules are recognised as being simple in structure, without carbon-hydrogen bonds and normally derived from inanimate materials, like minerals and the atmosphere.
Minerals are mainly oxides and sulphides which are strictly inorganic, as is most of the Earth and Universe.
Most industrial chemical production involves inorganic compounds and originated with the discovery and isolation of the elements.
Important concepts and definitions
The atom is a basic unit of matter consisting of a dense, central nucleus surrounded by a cloud of negatively charged electrons.
The atomic nucleus contains a mix of positively charged protons and electrically neutral neutrons (except in the case of Hydrogen-1, which is the only stable nuclide with no neutron).
The electrons of an atom are bound to the nucleus by the electromagnetic force.
Likewise, a group of atoms can remain bound to each other, forming a molecule, according to online publicly-contributed encyclopedia Wikipedia.
A molecule is defined as a sufficiently stable, electrically neutral group of at least two atoms, in a definite arrangement held together by very strong chemical bonds. It can also be defined as a unit of two or more atoms held together by covalent bonds.
A chemical reaction meanwhile, is an interactive process in which the constituent atoms of one or more substances, the reactants, are rearranged to create different substances as products.
Substances are either chemical elements or compounds and reactions always involve an energy change. Chemical reactions involve the exchange, sharing or interaction of the electrons between two or more atoms.
A reaction that requires energy to proceed is called endoergic and one that releases energy into the environment, often in the form of heat, is called exoergic.
The atoms of all elements are constructed from identical protons, neutrons and electrons and are distinguished by the number and arrangement of these subatomic particles.
Electrons are arranged in layers called shells around the nucleus, with each successive layer containing only a specific number of electrons. The number and configuration of electrons occupying the outer shell of an atom determine how it will interact with other atoms and are called valence electrons, and they determine the reactivity of the substance.
Substances with a full compliment of electrons in their outer shell are inactive chemically and are called inert. Hence the six noble gases that occur naturally, notably helium, neon, argon, krypton, xenon and radon, are of a very low chemical reactivity and considered inert.
The ease with which a given substance can achieve a full outer electron shell is an indicator of its chemical reactivity and the type of bonds likely to be formed during reactions.
The Periodic Table
In 1869 Russian scientist Dmitri Mendeleev devised a table of the known elements ordered by their atomic weights, but arranged ‘periodically’ by grouping elements with similar properties under each other.
Gaps were left for elements that were unknown at that time and their properties predicted (the elements were gallium, scandium and germanium). The order of elements was re-arranged if their properties later dictated it.
While the periodic table identifies individual elements, these are seldom found in isolation because most of them are highly reactive and therefore unstable in that form.
Instead chemicals are produced and transported as compounds, from which the desired elements can be released during the appropriate chemical processes.
In group 18 of the periodic table, the ‘noble gas’ atoms have completely filled electron shells and are almost completely inert. Most nonmetals have small atoms with nearly filled electron shells, requiring only a few additional electrons to assume the stable, noble-gas configuration.
Therefore, in the presence of other atoms, these nonmetallic atoms have pronounced tendencies to attract electrons to themselves (high electronegativities).
Inorganic chemicals in industry
Inorganic chemistry is a very practical scientific discipline forming the basis of large scale manufacturing of ‘basic’ or ‘commodity’ chemicals, with sulphuric acid (H2SO4) being by far the largest volume inorganic chemical produced.
Traditionally the volume of H2SO4 produced has been taken as an indicator of the size of a nation’s economy. Typically these chemicals are extracted from ores or brines, or as by-products of other processes. Manufacturing industries use them in the production of a diversity of other products.
The primary markets for commodity chemicals are industries manufacturing paper, building materials, motor vehicles, agricultural fertiliser, petroleum products, steel and other alloys, soaps and detergents, as well as being used in wastewater treatment.
An import category of inorganic chemicals that do occur naturally in their elemental form are the gases oxygen, nitrogen and argon – the primary products of the industrial gas industry.
Tonnage and bulk volumes of these are separated by the cryogenic distillation of air, while adsorbtion or membrane separation technologies are employed where applicable.
Helium and hydrogen are produced commercially as a by-product of natural gas.
Carbon dioxide is available in the off-gas of numerous processes and is often separated from the combustion products of fossil fuel combustion. Other inorganic products normally supplied as high-purity speciality gases include:
The chemical industry includes large, medium, and small companies that are located worldwide. Based on 2005 sales statistics, the top six companies comprised of BASF of Germany, Dow Chemical of the US, Shell Chemicals of the Netherlands/UK, Bayer of Germany, INEOS of the UK, and Exxon Mobil of the US.
The sales reported by these companies made up almost half of the industry’s turnover, while French industrial gases giant Air Liquide ranked 13th in the same year.