Do you know what pencil leads are made of? You call it pencil "leads" but it's actually a material called Graphite. Did you know it is pure Carbon, and nothing else? In this article, you will learn more about Graphite, it's structure and properties, and it's ever more interesting uses.
Graphite is formed naturally under high pressure and temperature conditions found between the Earth's crust and the Mantle. Graphite is found naturally in the China, Mexico, Canada, India, and Sri Lanka and some other countries.
- This article is about graphite.
- We will see its structure and its properties.
- Next, we will analyse the different types of graphite.
- We will see the uses of graphite to finish.
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 .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.
Did you know that Graphite, Charcoal, and Diamond are all allotropes of Carbon? The empirical formula of all of these three is just . They are all just a big molecule of Carbon! The only difference in them is the molecular structure i.e., the fundamental arrangement of atoms. You will learn about the structure of Graphite in this article. To learn about the structure of Diamond, head over to Diamond.
Allotropes are different structural forms the same element can exist in.
Carbon has the electronic configuration of 1s2 2s2 2p2. In the 2nd 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.
The Octet rule of chemical bonding states that elements try to make bonds with each other such that they all have 8 electrons in their valence shell. Having 8 electrons in the valence shell is considered to be a stable electronic configuration.
A Covalent Bond is a chemical bond which is formed when elements share electron-pairs with each other. To learn more about covalent bonds, head over to Covalent Bonding.
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!
You can check for Graphite's conducting behaviour yourself. Just make an electric circuit with a pencil lead, and you will see that the circuit is actually closed!
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.
Graphite is a non-metal but it is very similar to metals due to the properties it shares with them. Metals are also good conductors of heat, and metals also have free electrons which makes them good conductors of electricity - both properties which Graphite also has.
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.
When you write with your pencil, the Graphite lead of the pencil scratches against the paper. Due to the slippery nature of Graphite layers, some of the Graphite is left behind on the paper, which is why you are able to "write" with a pencil.
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 400oC. Because of its ability to withstand high temperatures, it is sometimes used as heat shields in nuclear reactors.
Although graphite is not recognized as highly flammable, it can catch fire in very hot and oxygen rich environment. When Oxygen is not present, it can be heated up to 3000oC.
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.
Graphite - Key takeaways
- Graphite is an allotrope of Carbon. Empirical formula of Graphite is .
- Graphite is formed under high heat and pressureconditions found between the Earth's crust and the upper mantle.
- Graphite consists of covalent bonds between Carbon atoms.
- In the structure of Graphite, each Carbon forms covalent bonds with 3 other Carbon atoms. This forms joined hexagonal rings of 6 Carbon atoms. The structure of Graphite consists of layers of sheets of these joined rings.
- Due to Carbon forming only 3 covalent bonds instead of 4, each Carbon has 1 free unpaired electron.
- The free unpaired electron is delocalized in the structure of Graphite i.e., it is free to move in the entire structure. This gives Graphite the property to conduct electricity.
- Due to weak intermolecular forces between layers, the layers can slide over each other. This property of Graphite allows it to be used in a number of uses including in pencil cores, and as lubricants.
- Carbon atoms in Graphite have strong covalent bonds which take a lot of energy to break. Due to this, Graphite has a high melting and boiling point.
- Graphite has high thermal stability i.e., it can withstand high temperatures without changing chemically. In the absence of Oxygen, it can withstand temperatures up to 3000oC.
- Graphite also has uses in electric motors, batteries, manufacturing of steel and glass, iron processing, and automotive brake linings.
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