Carbon: The element that shapes our world
Everywhere I look I see Carbon, from the plastic bottles in my refrigerator to my lunch. It is not only around us but within us too, as carbon composes 20% of all organic matter. Given this, it isn’t surprising that it has its own field of chemistry — Organic Chemistry! We see all around us that Carbon has become the basis of all life on planet Earth, but why so?
There are 118 elements in the periodic table. With 118 probable choices, why has nature chosen Carbon as the basis for all organic forms of life? Isn’t this interesting, intriguing? I am exploring this idea in the blog.
Consider these two factors:
- Stability, and
- Abundance
Stability is the most desired state in the universe. All elements strive to reach a ground state To understand this factor, we must first realise that Chemistry is driven by the forces of attraction. These are the forces that exist between different atoms and molecules allowing reactions to occur during which, these atoms and molecules try to attain most stability which is called the ground state. This usually occurs when atoms are able to attain noble gas configuration, and can be observed in the formation of covalent compounds.
Get Aarush Jhaveri’s stories in your inbox
Join Medium for free to get updates from this writer.
As we move across the periodic table from Group 1 to Group 14, the maximum number of covalent bonds an element can form increases step by step, reaching its peak at four in Group 14 (the Carbon group). Beyond this point, from Group 15 to Group 18, the bonding capacity gradually decreases again, eventually reaching zero in the noble gases. This means that elements in the Carbon group have the ability to form 4 covalent bonds as a result of them having 4 valence electrons. It would be like LEGO bricks being able to attach to other bricks from 4 sides instead of 2. Essentially, this tetravalency of Carbon gives it the ability to form complex and long molecules ranging from long stable polymer chains to aromatic closed rings and much more! The possibilities are endless! In fact, even our DNA is made up of a long polymer with a Carbon backbone.
On top of that, not only is Carbon the 2nd most abundant element in our body, but also the 4th most abundant in the solar system. Having so much of something just makes it easier to build from it. Imagine being built of Gold instead: There just isn’t enough of it on our planet!
Moving on, take a look at the Carbon Group on the Periodic Table. Carbon is right at the top, indicating to us that it has the smallest atomic radius and atomic mass and is hence the lightest element from that group. Additionally, it has only 6 electrons — 2 in the first orbital and 4 in the subsequent. This means that its valence electrons are closer to the nucleus, experiencing a greater electrostatic force of attraction. Thus, Carbon also has a greater first ionisation energy (energy required to remove 1 electron from 1 mole of a gaseous Carbon atom), while also forming strong covalent bonds. In fact, a C-C bond has a bond energy of approximately 350kJ/mol, far exceeding the bond energy of a Si-Si bond of 300kJ/mol.
Well, why only Carbon? Look at the periodic table — it has 117 elements, of which 94 are naturally occurring, that the universe could have chosen, but instead it chose Carbon.
Unlike Carbon all the elements in Groups 1–13 and 15–17 do not possess the same tetravalency that Carbon does and hence cannot form molecules large and complex enough. Noble gases are generally stable on their own and rarely form compounds. To contrast, take Oxygen: although it is an abundant element in both our planet and our bodies, it has only two valence electrons available for bonding. This restricts it to forming just two covalent bonds, limiting its ability to build large, complex structures in the way Carbon can.
Furthermore, one may choose to argue that Nitrogen too is significantly abundant and has 3 valence electrons, however the bond energy in a N-N bond is almost half of that in a C-C bond, making it difficult for molecules with a Nitrogen ‘backbone’ to withhold extreme conditions. Similarly, Boron also has 3 valence electrons however its issue is unique from the others in terms of its high rarity on our planet.
To conclude, it is Carbon’s uniqueness and its ability to suit our environment that allows it to form the basis of life on our planet Earth. However, on a far far planet in a galaxy a million light years away, it may not be impossible for us to expect to see life made of the riches of Gold we so dream for.
