Allotropic Forms Of Carbon

Allotropy meaning in chemistry is explained as the phenomenon where an element exists in more than one physical form.

What are Allotropes of Carbon?

Carbon is one of the most influential elements in nature that are present around us. It is represented by the symbol ‘C’ in the periodic table. It is one of the elements that show allotropy. The allotropes of carbon are categorized as amorphous or crystalline (Diamond, Graphite). Carbon with its variable states of oxidation and coordination numbers is one of the rare elements having multiple allotropic forms.

Allotropic Forms of Carbon

• Diamond: It is hard and transparent, where the carbon atoms are arranged in a tetrahedral lattice form. This is not a good conductor of electricity but is an excellent thermal conductor
• Lonsdaleite: Otherwise known as hexagonal diamonds
• Graphene: It is part of the basic structural elements that constitute other carbon allotropes, such as charcoal, nanotubes, and fullerenes
• Q-carbon: These are tough, brighter and harder than diamonds
• Graphite: It is a soft, and flaky solid, with moderate electrical conductivity. Here carbon atoms are bonded as in graphene and then layered in sheets
• Linear acetylenic carbon (Carbyne)

Graphite- Thermodynamically Stable Allotrope of Carbon

Graphite is a pure form of carbon. This is made of flat layers of carbon atoms arranged hexagonally. The material is soft, but slippery black solid. This property enables it to cut easily In each layer of graphite, one carbon atom is bonded to three other atoms through a C-C covalent bond. Here, each atom is sp² hybridized. The fourth bond is a pi bond due to the delocalization, mobility and electric conductivity of pi electrons Graphite is available in 2 forms: alpha and beta. In the former, the layers are in the sequence of ABAB with the third layer lying exactly over the first one. In the beta form, the layers are arranged in the form of ABCABC

Properties of Graphite

• This allotrope of carbon can be a lubricant due to its stacked-layer structure
• Its metallic cluster helps with electric conductivity. It is also a good thermal conductor
• Graphite is used as a dry lubricant in machines where we cannot use oil, especially at high temperatures
• Graphite is not reactive to acids and alkalis, so they are useful for making crucibles
• Graphite is the thermodynamically stable allotrope of carbon than diamond

Structure of Graphite:

Graphite has a unique structure of layered honeycomb. Atoms in each layer are in planar hexagonal rings where the carbon-carbon bond length inside is 141.5 picometres

Allotropes of Carbon Diamond

Diamond is the hardest material with strong covalent bonds. Covalent bonds are hard to break making this allotrope the hardest material on earth.

Structure of Diamond

This is one of the purest crystalline allotropes of carbon. Here, the carbon atoms are linked tetrahedrally. Each unit consists of one carbon bonded to four other carbon atoms that are bonded to other atoms. This gives this allotrope its three-dimensional structure of C-atoms.Each carbon atom here is sp3 hybridized and forms covalent bonds with the other four atoms tetrahedrally

Physical Properties of Diamond

• Hardest material
• Very high melting point
• High relative density
• Transparent in X-rays
• High refractive index value
• Bad conductor of electricity
• Good thermal conductor
• Insoluble in all solvents

Other Carbon Allotropes

Buckminsterfullerene

Buckminsterfullerene (C60) is another allotrope of carbon. Its structure is like a cage which looks similar to a football.

Fullerenes

They are spherical. These are made by evaporating graphite with the help of a laser. Unlike diamonds, these are soluble in organic solvents. The fullerene C60 is otherwise known as ‘Buckminsterfullerene’.