Carbon is placed at number 6 on the periodic table and is one of the most abundant elements in universe and in the earth’s crust. It is also the fundamental building block of all organisms. Hence, compounds of Carbon are known as organic compounds, and the study of Carbon compounds is known as Organic Chemistry.
Carbon occurs in nature in the free state as well as in the combined state as a compound with numerous other elements. In fact, after Hydrogen, it is the element that forms the most number of compounds with other elements.
Carbon is a key fragment of the major molecules that make up all living things on Earth. It is a significant part of glucose, proteins, fats, cellulose and DNA. Additionally, carbon is also a major component of rocks such as limestone and asphalt, fossil fuels such as natural gas and petroleum, wood, plastic and many more substances.
Carbon is found in the free state in nature in various forms, known as allotropes of Carbon.
What Is Allotropy?
Allotropy is the property of some chemical elements to exist in two or more different physical forms when found in the free state in nature. The various forms of the element are known as Allotropes. These allotropes exhibit different physical properties but the same graded chemical properties. Allotropy is the result of difference in the structural arrangement of the atoms of the element.
Carbon is one of the elements that display allotropy. There are several allotropes of carbon, both in the crystalline form as well as in the amorphous form.
Crystalline Allotropes of Carbon-
Carbon has two crystalline allotropes- diamond and graphite. Chemists created a third, new crystalline allotrope of Carbon in the laboratory and named it Fullerene. Here, we will take up only the two naturally occurring crystalline allotropes.
Diamond is a transparent, lustrous and extremely hard, crystalline form of Carbon.
Diamond is the hardest substance known to man. Each carbon atom is linked with four other carbon atoms in a tetrahedral form. This forms the crystalline structure of Diamond. This basic unit repeats itself and extends in all directions to form an octahedral lattice. Additionally, the bonds between the atoms are very strong covalent bonds, thus lending rigidity and hardness to the diamond crystal.
Owing to their hardness, diamonds are used in industry for cutting, drilling and grinding purposes. They are used in manufacturing semi-conductors. They are also used as precious gems in the most expensive of jewellery.
Graphite is a greyish black, lustrous and soft crystalline form of Carbon.
The structure of graphite is built up from a two-dimensional hexagonal unit, in which each carbon atom is linked to three other carbon atoms by covalent bonds in the same layer, thus giving it a sheet-like structure. The layers are arranged one above the other in parallel, held together by weak Van der Waals forces. This is the reason that graphite is a soft, slippery solid, which leaves a black mark on paper. Additionally, the crystal has mobile electrons in its structure, thus making it a good conductor of heat and electricity, even though it is a non-metal.
Owing to its soft nature, and ability to mark paper black, Graphite is used to make pencil leads and as a lubricant for heated machine parts, normal machine parts and bicycle chains. Since it is a good, stable conductor of electricity, it is used as an electrode in dry cells, electrolytic cells and electroplating, and in the manufacture of refractory cubicles.