Question

Which of the following is chemically inactive allotropic form of carbon? (a) Coal (b) Diamondl (c) Animal charcoal (d) Charcoal

Short answer

The chemically inactive allotropic form of carbon is diamond.

Step-by-step solution

Understanding Allotropes

Carbon exists in several different allotropic forms, which means it can exist in different structural modifications with distinct properties. The common allotropes of carbon include diamond, graphite, and amorphous forms like coal, charcoal, and carbon black.

Chemically Inactive Allotropes

An 'inactive' allotrope tends to be less reactive chemically due to its structural properties. Diamond is known to be a chemically inert form of carbon due to its strong covalent bonding and tetrahedral structure, making it hard and stable.

Eliminate Active Allotropes

Coal, animal charcoal, and charcoal are more chemically active compared to diamond. They contain a less rigid structure and are more likely to participate in chemical reactions.

Conclusion

Based on the properties that make an allotrope chemically inactive, diamond is uniquely stable and inert compared to other forms of carbon listed.

Key concepts

Chemical Inactivity

Chemical inactivity refers to the tendency of a substance to resist undergoing chemical reactions. In the context of carbon allotropes, this is determined by their structural properties. For instance, diamond is chemically inactive because of its rigid crystalline structure. Its carbon atoms are bonded in a tetrahedral lattice, which is incredibly stable and hard to break. This strong covalent bonding locks the atoms in place, preventing them from easily reacting with other substances. In contrast, more chemically active allotropes like coal and charcoal have less organized structures. Their atoms are not as tightly bound, allowing them to engage more readily in chemical reactions. Hence, while diamond resists interactions with other chemicals, these other allotropes can be reactive due to their less defined arrangements.

Diamond Structure

The structure of diamond is a marvel of nature, crafted entirely from carbon atoms. In a diamond, each carbon atom is covalently bonded to four other carbon atoms in a three-dimensional tetrahedral structure. These bonds are incredibly strong, creating a robust and stable configuration. This explains why diamond is one of the hardest materials known to man.
Furthermore, the tightly packed atoms in diamond leave no room for impurities, contributing to its transparency and brilliance. The arrangement also means that diamond, as a whole, is less fault-prone, making it chemically inert. Thus, it is not merely the composition but the intricate bonding and uniform structure that render diamond chemically inactive.

Carbon Bonding

Understanding carbon bonding is essential to grasp why some allotropes are chemically inert while others are not. Carbon atoms can form various types of bonds, including single, double, and triple bonds. In the case of diamond, the carbon atoms form strong single covalent bonds in a tetrahedral pattern.
This covalent bonding controls the reactivity of the allotrope since it dictates how easily atoms might break free from each other. Reactions often require breaking existing bonds, and in diamond, this is a herculean task due to its robust structure. Consequently, different forms of carbon bond differently: diamonds form strong covalent networks, whereas graphite and amorphous forms like coal have layers or irregular bonding, allowing easier chemical interactions.

Chemically Active Allotropes

While diamond is a notable example of chemcial inactivity, other allotropes of carbon are quite reactive. Chemically active allotropes include graphite, coal, and charcoal, each having their distinct characteristics but sharing the trait of greater reactivity. These materials possess less rigid structures compared to diamond.
For instance, in graphite, carbon atoms are arranged in layers with weaker bonds between them, allowing the layers to slide over one another. This makes graphite reactive and a good conductor of electricity. Coal and charcoal, on the other hand, have more amorphous arrangements with different atoms and impurities that facilitate chemical reactions. These unique structures afford them a versatility that diamond lacks, making them valuable in various chemical processes.