Carbon:Life's most important element

THE CHINGCHOK Hunter

Carbon:Life's most important element Without carbon, life as we know it would not exist Writer: DAVID CANAVAN Published: 21/07/2009 at 12:00 AM Newspaper section: Learningpost

Anything living (or dead, for that matter) contains carbon, as does the fuel for cars and motorbikes, all plastics and even wax candles and lightweight carbon fibres. Carbon is simply omnipresent.

The versatile element carbon has several allotropes. Note that graphite, right, has a simple, flat structure while diamond, left, is very complex in structure, which is what makes diamond unusually tough and resilient. WIKIMEDIA COMMONS

chaitc Special properties

What makes carbon so special is its chemical properties, which determine its many physical qualities. Carbon has the chemical symbol ''C'' and is in group four of the periodic table. It has an atomic number of 6. This means it has six electrons overall: two in the first electron shell and four in its outer electron shell, which is why it is in group four.

Basically, what this means is that it has four electrons to gain in order to complete its outer shell, which means, with carbon being a non-metal, it can use the four outer electrons it already has and it can share these with other elements to form covalent bonds. It is this unique ability that makes carbon so special and allows it to form more compounds than any other element.

chaitc Allotropes

An allotrope is another form of the same element. This is possible because the structure of the atom affects the chemical and physical properties. For example, graphite, charcoal and diamond are different forms of the same element _ carbon. Carbon can take many solid forms with many physical properties, depending on how it bonds.

A diamond is the hardest natural substance. Under immense pressure and heat, carbon atoms bond together in a tetrahedral structure (see graphic, above right), with every carbon sharing each of its four bonds with four other carbon atoms in a shape with a carbon atom in the middle, one above and three in a tripod shape below, repeating many times.

This structure gives diamond incredible strength and hardness. All carbon allotropes form diamonds when subjected to enough pressure and heat. Because diamond is so hard, only a diamond can cut another diamond.

Diamond-edged machinery, though, doesn't use the fancy sparkling versions you see on rich people's fingers. Rather, they are made up of diamonds that are dull and not very attractive.

Another allotrope of carbon is graphite, a relatively soft material. Everyone has used graphite before, because one form of graphite is the pencil lead, which, of course, isn't lead at all. It is exactly the same stuff as diamond, but with a different structure. Instead of each carbon bonding to four others, it now only bonds to three others in a hexagonal flat plane (see graphic, above right).

Each hexagonal layer is weakly attracted to layers on top and below it, and they can slide over each other easily. Therefore, when you write with a pencil, you are simply allowing layers of carbon to slide over each other, leaving a carbon trail on your page!

Graphite is also the only non-metal that conducts electricity. This is because the extra electron that isn't used in bonding, due to only bonding to three other carbons, can now move within the graphite and allows electricity to flow.

There are many other allotropes of carbon, including the fullerenes, but their applications are still under research, although there may be cancer cures and applications in nanotechnology, so researchers are continuously finding new ways to use carbon.

Chaitc Isotopes

Because carbon structures that are made up of lots of carbon atoms can differ, the carbon atoms themselves can also take different forms. For an element to remain as carbon and not as boron or nitrogen, it needs to always have six electrons and six protons. Most carbon atoms also have six neutrons, but there are cases where the number of neutrons changes. This doesn't chemically alter carbon, but it can make it radioactive.

Normal carbon is known as carbon 12 due to its six protons and six neutrons but there are two naturally occurring isotopes of carbon, which means there are two forms of carbon that have different numbers of neutrons. Carbon 13 has six protons but seven neutrons, and the famous allotrope carbon 14 has six protons and eight neutrons. This is radioactive and is used in carbon dating.

There are constant traces of C14 in living organisms that steadily decay at a constant rate when an organism dies, known as a half life. By analysing the amount of C14 in the dead organism, the age can be accurately assessed, which is the principal behind carbon dating.

chaitc Organic chemistry

The term ''organic chemistry'' often sends shivers down many peoples' spines as they recall the complex and often mind-boggling lessons they endured. It is basically the chemistry of living things, where large, complex chemicals of carbon, hydrogen and often oxygen and other elements interact.

Inorganic carbon compounds are simpler compounds containing carbon, such as carbon monoxide, carbon dioxide and limestone (composed mainly of calcium carbonate). Organic carbon compounds make life possible and are the basis of all life on Earth.

Crude oil and natural gas are the remains of once-living organisms and therefore contain carbon bonded to hydrogen, or hydrocarbons. From crude oil, many substances are made, including ethanol, methane, petrol, aviation fuel, diesel and bitumen. Carbon is also used in plastics and carbon fibre products.

When carbon and hydrogen are bonded with oxygen, they form carbohydrates, alcohols and fats. Throw in some nitrogen and you have amino acids and proteins. With phosphorus and sulphur involved, you have the ingredients for DNA (deoxyribonucleic acid) and the energy-giving molecule ATP (adenosine triphosphate), all of which are possible because of the carbon-carbon spine.

Carbon really is everywhere! In fact, I challenge you to find something that doesn't contain carbon. Even steel is a combination of iron and carbon! You can't live or exist without it. It is the most important element to life, and should we find life on any other planet, I would bet that the foundation of it would be carbon. What an element!

David Canavan has an MSc in Behavioural Ecology and is the Head of Secondary at Garden International School. David is fascinated by science and loves animals, especially the dangerous kind! You may contact him at davidc@gardenbangkok.com .

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