|Group||14||Melting point||3825 oC, 6917 oF, 4098 K|
|Block||p||Density (kg m-3)||3513 (diamond); 2267 (graphite)|
|Atomic number||6||Relative atomic mass||12.011|
|State at room temperature||Solid||Key isotopes||12C, 13C, 14C|
|Electron configuration||[He] 2s22p2||CAS number||7440-44-0:1333-86-4|
|ChemSpider ID||4575370||ChemSpider is a free chemical structure database|
The three crowns represent the three major forms of the element in nature and carbon’s status as ‘King of the Elements’ in the Periodic Table.
Diamond is a colourless, transparent, crystalline solid and the hardest known material. Graphite is black and shiny but soft. The nano-forms, fullerenes and graphene, appear as black or dark brown, soot-like powders.
Impure carbon in the form of charcoal (from wood) and coke (from coal) is used in metal smelting. It is particularly important in the iron and steel industries.
Graphite is used in pencils, to make brushes in electric motors and in furnace linings. Activated charcoal is used for purification and filtration. It is found in respirators and kitchen extractor hoods.
Carbon fibre is finding many uses as a very strong, yet lightweight, material. It is currently used in tennis rackets, skis, fishing rods, rockets and aeroplanes.
Industrial diamonds are used for cutting rocks and drilling. Diamond films are used to protect surfaces such as razor blades.
The more recent discovery of carbon nanotubes, other fullerenes and atom-thin sheets of graphene has revolutionised hardware developments in the electronics industry and in nanotechnology generally.
150 years ago the natural concentration of carbon dioxide in the Earth’s atmosphere was 280 ppm. In 2013, as a result of combusting fossil fuels with oxygen, there was 390 ppm. Atmospheric carbon dioxide allows visible light in but prevents some infrared escaping (the natural greenhouse effect). This keeps the Earth warm enough to sustain life. However, an enhanced greenhouse effect is underway, due to a human-induced rise in atmospheric carbon dioxide. This is affecting living things as our climate changes.
Living things get almost all their carbon from carbon dioxide, either from the atmosphere or dissolved in water. Photosynthesis by green plants and photosynthetic plankton uses energy from the sun to split water into oxygen and hydrogen. The oxygen is released to the atmosphere, fresh water and seas, and the hydrogen joins with carbon dioxide to produce carbohydrates.
Some of the carbohydrates are used, along with nitrogen, phosphorus and other elements, to form the other monomer molecules of life. These include bases and sugars for RNA and DNA, and amino acids for proteins.
Living things that do not photosynthesise have to rely on consuming other living things for their source of carbon molecules. Their digestive systems break carbohydrates into monomers that they can use to build their own cellular structures. Respiration provides the energy needed for these reactions. In respiration oxygen rejoins carbohydrates, to form carbon dioxide and water again. The energy released in this reaction is made available for the cells.
Carbon is found in the sun and other stars, formed from the debris of a previous supernova. It is built up by nuclear fusion in bigger stars.
It is present in the atmospheres of many planets, usually as carbon dioxide. On Earth, the concentration of carbon dioxide in the atmosphere is currently 390 ppm and rising.
Graphite is found naturally in many locations. Diamond is found in the form of microscopic crystals in some meteorites. Natural diamonds are found in the mineral kimberlite, sources of which are in Russia, Botswana, DR Congo, Canada and South Africa.
In combination, carbon is found in all living things. It is also found in fossilised remains in the form of hydrocarbons (natural gas, crude oil, oil shales, coal etc) and carbonates (chalk, limestone, dolomite etc).
Molar heat capacity
(J mol-1 K-1)
|6.155 (diamond); 8.517 (graphite)||Young's modulus (GPa)||1050 (diamond)|
|Shear modulus (GPa)||478 (diamond)||Bulk modulus (GPa)||542 (diamond);33 (graphite)|
Carbon occurs naturally as anthracite (a type of coal), graphite, and diamond. More readily available historically was soot or charcoal. Ultimately these various materials were recognised as forms of the same element. Not surprisingly, diamond posed the greatest difficulty of identification. Naturalist Giuseppe Averani and medic Cipriano Targioni of Florence were the first to discover that diamonds could be destroyed by heating. In 1694 they focussed sunlight on to a diamond using a large magnifying glass and the gem eventually disappeared. Pierre-Joseph Macquer and Godefroy de Villetaneuse repeated the experiment in 1771. Then, in 1796, the English chemist Smithson Tennant finally proved that diamond was just a form of carbon by showing that as it burned it formed only CO2.
|Listen to Carbon Podcast|
Chemistry in Its Element - Carbon
You're listening to Chemistry in its element brought to you by Chemistry World, the magazine of the Royal Society of Chemistry
Hello, this week to the element that unites weddings, wars, conflicts and cremations and to explain how, here's Katherine Holt.
Any chemist could talk for days about carbon. It is after all an everyday, run-of
-the-mill, found-in-pretty-much-everything, ubiquitous element for us carbon-based life forms. An entire branch of chemistry is devoted to its reactions.
In its elemental form it throws up some surprises in the contrasting and fascinating forms of its allotropes. It seems that every few years a new form of carbon comes into fashion - A few years ago carbon nanotubes were the new black (or should I say 'the new bucky-ball') - but graphene is oh-so-now!
But today I'm going to talk about the most glamorous form that carbon can take - diamond. For millennia diamond has been associated with wealth and riches, as it can be cut to form gemstones of high clarity, brilliance and permanence. Diamonds truly are forever! Unfortunately, diamond also has a dark side - the greed that diamond induces leads to the trade of so-called 'conflict diamonds' that support and fund civil wars.
Mans desire for diamond has led alchemists and chemists over many centuries to attempt to synthesise the material. After many fraudulous early claims diamond was finally synthesised artificially in the 1950s. Scientists took their inspiration from nature by noting the conditions under which diamond is formed naturally, deep under the earth's crust. They therefore used high temperatures (over 3000oC) and high pressures (>130 atms) to turn graphite into carbon. This was an impressive feat, but the extreme conditions required made it prohibitively expensive as a commercial process. Since then the process has been refined and the use of metal catalysts means that lower temperatures and pressures are required. Crystals of a few micron diameter can be formed in a few minutes, but a 2-carat gem quality crystal may takes several weeks.
These techniques mean its now possible to artificially synthesise gemstone quality diamonds which, without the help of specialist equipment, cannot be distinguished from natural diamond. It goes without saying that this could cause headaches among the companies that trade in natural diamond! It is possible to turn any carbon based material into a diamond - including hair and even cremating remains! Yes - you can turn your dearly departed pet into a diamond to keep forever if you want to! Artificial diamonds are chemically and physical identical to the natural stones and come without the ethical baggage. However, psychologically their remains a barrier - if he really loves you he'd buy you real diamond - wouldn't he?
From the perspective of a chemist, materials scientist or engineer we soon run out of superlatives while describing the amazing physical, electronic and chemical properties of diamond. It is the hardest material known to man and more or less inert - able to withstand the strongest and most corrosive of acids. It has the highest thermal conductivity of any material, so is excellent at dissipating heat. That is why diamonds are always cold to the touch. Having a wide band gap, it is the text book example of an insulating material and for the same reason has amazing transparency and optical properties over the widest range of wavelengths of any solid material.
You can see then why diamond is exciting to scientists. Its hardness and inert nature suggest applications as protective coatings against abrasion, chemical corrosion and radiation damage. Its high thermal conductivity and electrical insulation cry out for uses in high powered electronics. Its optical properties are ideal for windows and lenses and its biocompatibility could be exploited in coatings for implants.
These properties have been known for centuries - so why then is the use of diamond not more widespread? The reason is that natural diamond and diamonds formed by high pressure high temperature synthesis are of limited size - usually a few millimeters at most, and can only be cut and shaped along specific crystal faces. This prevents the use of diamond in most of the suggested applications.
However, about 20 years ago scientists discovered a new way to synthesise diamond this time under low pressure, high temperature conditions, using chemical vapour deposition. If one were to consider the thermodynamic stability of carbon, we would find that at room temperature and pressure the most stable form of carbon is actually graphite, not diamond. Strictly speaking, from a purely energetic or thermodynamic point of view, diamond should spontaneously turn into graphite under ambient conditions! Clearly this doesn't happen and that is because the energy required to break the strong bonds in diamond and rearrange them to form graphite requires a large input of energy and so the whole process is so slow that on the scale of millennia the reaction does not take place.
It is this metastability of diamond that is exploited in chemical vapour deposition. A gas mixture of 99 % hydrogen and 1 % of methane is used and some activation source like a hot filament employed to produce highly reactive hydrogen and methyl radicals. The carbon-based molecules then deposit on a surface to form a coating or thin film of diamond. Actually both graphite and diamond are initially formed, but under these highly reactive conditions, the graphitic deposits are etched off the surface, leaving only the diamond. The films are polycrystalline, consisting of crystallites in the micron size range so lack the clarity and brilliance of gemstone diamond. While they may not be as pretty, these diamond films can be deposited on a range of surfaces of different size and shapes and so hugely increase the potential applications of diamond. Challenges still remain to understand the complex chemistry of the intercrystalline boundaries and surface chemistry of the films and to learn how best to exploit them. This material will be keeping chemists, materials scientists, physicists and engineers busy for many years to come. However, at present we can all agree that there is more to diamond than just a pretty face!
Katherine Holt extolling the virtues of the jewel in carbon's crown. Next week we're heading to the top of group one to hear the story of the metal that revolutionised the treatment of manic depression.
Its calming effect on the brain was first noted in 1949, by an Australian doctor, John Cade, of the Victoria Department of Mental Hygiene. He had injected guinea pigs with a 0.5% solution of lithium carbonate, and to his surprise these normally highly-strung animals became docile. Cade then gave his most mentally disturbed patient an injection of the same solution. The man responded so well that within days he was transferred to a normal hospital ward and was soon back at work.
And it's still used today although despite 50 years of medical progress we still don't know how it works. That was Matt Wilkinson who will be here with the story of Lithium on next week's Chemistry in its Element, I do hope you can join us. I'm Chris Smith, thank you for listening and goodbye.
Chemistry in its elementis brought to you by the Royal Society of Chemistry and produced by thenakedscientists dot com. There's more information and other episodes of Chemistry in its element on our website at chemistryworld dot org forward slash elements.
Mining and Sourcing data: British Geological Survey – natural environment research council.
Text: John Emsley Nature’s Building Blocks: An A-Z Guide to the Elements, Oxford University Press, 2nd Edition, 2011.
Additional information for platinum, gold, neodymium and dysprosium obtained from Material Value Consultancy Ltd www.matvalue.com
Data: CRC Handbook of Chemistry and Physics, CRC Press, 92nd Edition, 2011.
G. W. C. Kaye and T. H. Laby Tables of Physical and Chemical Constants, Longman, 16th Edition, 1995.
Members of the RSC can access these books through our library.