Graphite

Structure of Graphite

To understand the structure of a molecule, we first have to know what elements the molecule consists. And Graphite just consists of Carbon. That's it! The empirical formula of Graphite is $\mathbf{C}$.Do you find it odd? It's not if you understand that of all elements in the periodic table, Carbon holds the special ability to form large molecules with long chains of Carbon.

Carbon has the electronic configuration of 1s2 2s2 2p2. In the 2^nd shell of Carbon (the valence shell) Carbon has 4 electrons. It needs 4 more electrons to complete its octet and have a stable electronic configuration. To do this, Carbon makes 4 covalent bonds. By making 4 covalent bonds, Carbon shares 4 of its electrons with other atoms, and in return other atoms share 4 electrons with Carbon.

Fig. 1: Structure of Graphite | Flash Education

Fig. 2: Top view of a layer of Graphite | Engineering Choice

In Graphite, each Carbon atom only makes 3 bonds with other Carbon atoms. This results in the formation of hexagonal rings of 6 carbon atoms, and layers of such rings. You must be thinking, if Carbon is only making 3 covalent bonds, it must have a free unpaired electron. If you though of that, you are right. Each Carbon atom has one free unpaired electron in the structure. These unpaired electrons form weak intermolecular bonds between layers of Graphite. These weak intermolecular bonds are represented by the blue dotted lines in the figure. But these free unpaired electrons are delocalized in the structure of Graphite. That means that they are not constrained to any single Carbon atom, and are free to move around in the entire structure. Due to this unique phenomenon, Graphite is able to conduct electricity!

Properties of Graphite

You have already seen some properties of Graphite while discussing its structure. In this section, we will discuss more of its properties.

Good Conductor of Electricity and Heat

You have already seen in the previous section what makes Graphite a good conductor of electricity. The free unpaired electron of each Carbon atom is delocalized and is free to move in the entire structure of Graphite. These electrons facilitate the flow of charge and hence the flow of electric current. Due to the same phenomenon, Graphite is also a good conductor of heat.

High Melting/Boiling Point

The Carbon atoms share very strong covalent bonds in the structure of Graphite. The hexagonal ring arrangement also contributes to the strength of the structure. Due to this, a lot of energy is required to break the bonds, contributing to the high melting and boiling point.

Soft and Slippery

Carbon atoms in the structure of Graphite do not have covalent bonds between layers. The layers are held together by weak intermolecular forces. Due to this, the layers can easily slip and slide over one another. This property makes Graphite soft, and ideal to be used as a lubricant.

High Thermal Stability

Graphite can be heated to very high temperatures without affecting it at all. It is considered as thermally stable. Ignition temperature of Graphite is 400^oC. Because of its ability to withstand high temperatures, it is sometimes used as heat shields in nuclear reactors.

Types of Graphite

There are two types of Graphite according to variation in its structure. The layers of Graphite can be arranged with respect to each other in two ways. According to this arrangement, Graphite is of two types - Alpha Graphite and Beta Graphite.

Alpha Graphite

Fig. 3: ABA or Bernal Stacking in Graphite | ResearchGate

In Alpha Graphite, subsequent layers are arranged in ABABAB fashion, as shown in the figure. Each alternate layer is in the same position. Half of the atoms of a layer are directly over atoms of the layer beneath it, and the other half of atoms are directly over the centre of a hexagon in the layer beneath. This arrangement of layers is also called Bernal Stacking of layers in Graphite.

Beta Graphite

Fig. 4: ABC or Rhombohedral Stacking in Graphite | ResearchGate

In Beta Graphite, the layers are stacked in ABCABC fashion, as shown in the figure. Every 3rd layer is in the same position. This arrangement of layers is also known as Rhombohedral Stacking of layers in Graphite.

Uses of Graphite

Graphite has a varied use because of its unique properties.

• You already know about their use in pencils. Pencil cores are made from a mixture of Graphite and clay. Pencils use their property of weak intermolecular forces, and how layers can slide over each other and get deposited on a surface if "written" upon.
• When in contact with moisture in the atmosphere, Graphite's lubricating property enhances. Due to this, Graphite is used in automotive brake linings.
• Combining its lubricating properties with its ability to conduct electricity, Graphite is used in electric motors for moving electrical contacts. This allows the electric circuit to be closed even with moving contacts while reducing friction.
• Graphite is used in the manufacturing of steel, iron processing, and glass making because of its ability of withstand high temperatures without changing chemically.
• Lithium-ion batteries, the batteries used in cell-phones, uses Graphite for its anode.
• Graphene, a derivative of Graphite is one of the strongest materials identified in the world - it is stronger than steel while being significantly lighter. Graphene is thin rolled sheets of Graphite.