Carbon Allotropes ✖ Shostakovich

Background reading music curated for this article is available at the bottom. Click to enjoy

01 Introduction

One of the most common elements in the earth is carbon. It is fundamental to life and is involved in various natural and chemical reactions. One unique characteristic of carbon is its ability to form four covalent bonds with other molecules which allow it to combine with other elements and form numerous complex and stable structures including carbon dioxide and biological molecules such as DNA. The element is found in various parts of the earth ranging from the atmosphere, water, soil, and fossil fuels and constantly undergoes various reactions in the cycle of carbon. There are several forms of carbon with distinct characteristics.

01-1  Graphite / Graphene

Graphite is an allotrope on the macroscale made up of layers of carbon atoms in a hexagonal honeycomb network stacked together. 

graphite and its structure

Each carbon is sp2 hybridized, and hence there are three strong σ bonds within the same plane, with the fourth electron occupying a π bond above and below the plane. In graphite, therefore, there are strong bonds in the plane but weak van der Waals forces between layers, and hence the resultant anisotropy is manifested as excellent electrical conductivity and strength along the planes, while there is weak resistance to shearing between the planes. 

One atomic layer of graphite is referred to as Graphene, and it is characterized by extraordinary electron mobility, ballistic transport across submicron lengths, and very high tensile strength owing to the uninterrupted π conjugation. 

graphene and single-layer structure

Graphite is commonly used as a dry lubricant, electrode material, and neutron moderator, while graphene is the core component of many advanced technologies ranging from flexible electronics to nanocomposites.

01-2  Diamond

The crystal structure of Diamond consists of a three-dimensional covalent bond network in which every carbon atom is sp³-hybridized and bonded tetrahedrally with four other carbon atoms in the network. 

diamond structure

The extended network of the sigma bonding makes the material extremely hard, has a very high Young’s modulus, and is highly resistant to deformation; hence, it is the hardest natural substance. The lack of delocalized electrons in the lattice network results in a wide band gap (~5.5 eV); therefore, Diamond is an electrical insulator. However, it is a good conductor of heat because of efficient phonon transport by virtue of its stiff lattice structure. It is transparent in the visible light region along with a high refractive index to give brilliant dispersion, which is useful in gemstones.

diamond cutter

Diamond finds various uses in industry like cutting, drilling, grinding, and polishing tools, and is used as a heat spreader in electronic devices.

01-3  Fullerene

Fullerenes are discrete allotropes of carbon that exist as cage-shaped molecules constructed from both pentagonal and hexagonal rings. The surface structure is therefore bent and strained is minimized in order to provide a hollow core structure. Carbon atoms usually have sp² hybridization but they exhibit non-planar structures because of the presence of π-orbital curvature and localized electrons.

fullerene's football-like structure

Buckminsterfullerene is the most studied fullerene that is shaped like a soccer ball and has very high symmetry (Ih point group). This bending modifies the electronic properties of the fullerenes in a way that leads to discrete molecular orbitals, electron accepting ability, and distinctive redox properties. Endohedral fullerenes are possible through the formation of complexes in which other atoms or ions can be trapped within the molecular structure. They can also be functionalized heavily for the purpose of having different chemical properties. Uses include organic solar cells as electron acceptors, drug delivery in biomedicine, lubrication because of low shearing interactions between fullerenes, and superconductivity upon doping with alkali metals.

Endnote

The music of this topic goes to Dmitri Shostakovich's Cello Concerto No. 1 in E-flat major.

Dmitri Shostakovich Cello Concerto No.1 in E-Flat Major

6:35

Diamond is rigid, intensely ordered, and extremely strong due to its 3D tetrahedral bonding network. Shostakovich’s concerto reflects this with its sharp contrasts, crystalline textures, and structural tension. The solo cello cuts through the orchestral “lattice” like a highly focused beam of energy. Its brilliance and emotional pressure resemble the hardness and optical clarity of diamond.