An Introduction to Carbon
We are aware that the amount of carbon present in the earth’s atmosphere and its crust is very less. There is only 0.02% of carbon in the earth’s crust. This carbon exists as minerals like coal, carbonates and hydrogen carbonates etc. 0.03 % of the carbon exists in the atmosphere of the earth as carbon dioxide.
Well, do not underestimate the importance of carbon based only on its percentage of availability. Carbon is utmost important for our existence and it finds an extensive usage in chemistry. Because of its indisputable importance, chemistry has been divided into two branches:
Thus, you must know that carbon is an essential part of every living organism as we are all organic beings!
The Anomalous Behaviour of Carbon
We must remember that most of the first members of a group have peculiar characteristics and properties. On similar grounds, even carbon behaves differently than the other members of the group. The properties of carbon are very unique. We can attribute this behaviour to carbon mainly due to :
Let us now look at some of these anomalies and their causes in more details.
Unique Properties of Carbon
1) The Small Size of Carbon
Carbon derives a lot of its properties from its small size. The compounds that carbon forms are highly stable and this is also because of its small size. Due to its small size, the nucleus effectively holds on to the bonded and non-bonded electrons.
Hence in short, tetravalency, small size and property of catenation make carbon different from other elements and so we have the whole branch of chemistry dedicated to the study of this kind of compound.
2) Tetravalency of Carbon
Carbon exhibits tetravalency. It means it can share four electrons to complete its octet. Thus, we know it bonds to four different monovalent atoms. Carbon forms a large variety of compounds with oxygen, nitrogen, hydrogen, halogens. This results in a different set of compounds which have distinctive characteristics and properties.
Carbon has the availability of only s and p orbitals. Therefore, it can hold only four pairs of electrons in its valence shell. Thus, we can restrict the covalence to four. However, the other elements in the group can easily grow their covalence due to the availability of d-orbitals.
One of the unique properties of Carbon is its ability to form long carbon chains. It implies that carbon attaches with other carbon atoms to form long carbon chains. This property is what we call as catenation. Sometimes, this chain could be as big as to have a total of 70-80 carbons. This gives rise to a variety of complex compounds. Some of the compounds have a straight carbon chain while some others have branched carbon chain or rings.
The carbon compounds having only single bond are the saturated hydrocarbons. On the other hand, the compounds with double or triple bond are the unsaturated hydrocarbons.
As we move down the group, the size of the elements increases. This results in a decreasing electronegativity. Thus, the propensity to show catenation also decreases. This can be clearly observed from bond enthalpy values. The catenation order is C >> Si > Ge >> Sn.
Additionally, carbon has an extraordinary capacity to shape pp – pp multiple bonds with itself and with different molecules. This can also be related to its smaller size and high electronegativity. Some of the examples would include C = C, C° C, C = O, C = S and C° N.
As a matter of fact, the heavier elements don’t shape pp – pp bonds. This is mainly because of the reason that their nuclear orbitals are too vast and diffused to have viable overlapping. For example, lead does not indicate catenation.
Q: Give some practical uses of carbon.
Ans: There are many important uses of carbon. Some of them are: