Question

Why are alkanes relatively unreactive?

Answer 1

In organic chemistry, the compounds which are composed of hydrogen and oxygen atoms only are known as hydrocarbons. The hydrocarbons are broadly divided into two types: saturated hydrocarbons, compounds which only contain sigma bonds and unsaturated hydrocarbons in which pi bonds are present as well.

Complete answer:
Alkanes are the saturated hydrocarbons which can be generally represented by the formula ${C_n}{H_{2n + 2}}$. The carbon atoms in the structure of alkane are covalently bonded to hydrogen atoms and other carbon atoms via single bonds. The bonds formed within an alkane i.e., carbon-carbon single bonds and carbon-hydrogen double bonds are very strong because they consist of sigma bonds which are formed by good overlapping of orbitals. Also, the bonds formed between carbon and hydrogen atoms are very slightly polar because of the negligible electronegativity difference between the atoms.
In case of unsaturated compounds i.e., alkenes and alkynes are more reactive than alkanes because a chemical reaction proceeds by transferring of electrons and breaking of bonds and we know that pi bonds present in unsaturated compounds are much weaker than sigma bonds, due to which the cleavage of a bond is easier in unsaturated compounds and hence are relatively more reactive than alkanes.
Hence, under normal conditions, alkanes are considered chemically unreactive.

Note:
It is important to note that although alkanes are relatively unreactive but the alkane burns very rapidly in the presence of air or oxygen to undergo combustion reaction. Because when combustion reactions take place, a large amount of heat is released during the process to form carbon dioxide and water and hence alkanes are widely used as fuels as they produce large amounts of heat.