High-level research investigation. Received full marks (20/20). This a very detailed and comprehensive guide on how to structure your report while being concise and informative to hit the criteria.
Compression strength, electrical and thermal conductivity, and
density between diamond and graphite.
Claim:
The structure of allotropes determines their properties.
Rationale:
The claim chosen, ‘the structure of allotropes determines their properties’ has many aspects that can be
investigated. An allotrope is a chemical element with two or more different atom arrangements
(Britannica, 2017). Allotropes are alike in most of the chemical properties but highly differ in physical
properties (Infoplease, 2017). There are many elements that exhibit allotropy such as oxygen, sulfur and
carbon. All have numerous allotropes, nevertheless carbon allotropes are more commonly known.
Diamond and graphite are common examples of carbon allotropes. Both allotropes have very different
areas of application. According to Somarin (2014) the major uses of diamond are through construction,
mining and machinery manufacturing. In contrast, graphite is most commonly used in pencils, batteries
and high temperature lubricants. The applications are different as a result of their contrasting physical
properties. The chemical properties of these minerals are identical as they are composed of carbon.
Diamond is an electrical insulator (has high electrical resistivity) and is rated a 10 on the Mohs scale of
mineral hardness. On the contrary graphite is an electrical conductor (has low electrical resistivity) and
has a hardness of less than one on the Mohs hardness scale (Rossi, 2007). Their variating physical
properties is a result of their own distinct structures. While the carbon atoms in diamond form a
tetrahedral system, graphite is layered with atoms arranged in horizontal sheets thus creating a
hexagonal structure (Britannica, 2022).
Data collected from Miyoshi Kazuhisa (1998), Helmenstine (2019) and Rand David (2018) will be utilised
and analysed in this report to determine if the structure of diamond and graphite will affect their
properties. Ultimately this investigation is to find data that will support the claim.
Research question:
How does the structures of diamond and graphite (both allotropes of carbon) determine their physical
properties such as compressive strength, electrical conductivity, density and their applications?
Background:
In a diamond, each carbon atom shares its electron with four other carbon atoms forming four covalent
bonds. This particular bonding is due to the S p 3 hybrid orbitals which is resulted from the combination
of 1 s-orbital and 3 p-orbitals to form four equivalent orbitals. As it is S p 3 hybridised, diamond has 25%
s-character. The bond length of C-C bond is 154pm with a bond angle of 109.5 degrees (BYJU’S, 2021).
Hence, the tetrahedrally arranged atoms form a rigid three-dimensional lattice structure. Within the
structure, the electrons are held tightly together so the electrons aren’t allowed to move freely (Akash,
2021). Since there are no free electrons and no ions, electric current gets resisted by diamond making it
a very good insulator (poor conductor).
Chemistry Research Investigation 2022
, Graphite, on the other hand, has a hexagonal structure as it has S p2 hybrid orbitals. It occurs when 1 s-
orbital and two p-orbitals form into 3 equivalent orbitals. This is also as all the carbon atoms form
chemical bonds with three other carbon atoms. Each of the carbon atoms have one electron that isn’t
bonded with another. The C-C bond lengths is 145pm with a bond angle of 120 degrees. Since it is S p2
hybridised, it has 33% s-character meaning the bonds are shorter, stronger and more stable when
compared to diamond (BYJU’S, 2021). From research in Libre texts (2021), the hexagonal rings create
layers composed of graphene sheets which are stacked parallel to each other (on top of each other).
Between the layers there are weak attractive forces called Van der Waals forces holding them together.
As the last electron of the carbon atoms have been delocalised it enables it to freely move around the
whole sheet. These spare electrons allow graphite to conduct electricity thus it is a good conductor (or a
poor insulator). Similar to diamond, the atoms of graphite are held together through covalent bonding
making each layer strong.
In both structures, the carbon atoms are held by covalent bonding which requires high temperatures to
break thus diamond and graphite both have high melting point. Diamond has a melting point of 4226
degrees Celsius (4500 degrees kelvin) while graphite has 3926 degrees Celsius (4200 degrees kelvin).
Although they share similar melting points other physical properties such as compressive strength
(ability to resist compression), electrical and thermal conductivity (the degree to which a material
conducts electricity and heat), and density (degree of compactness of a substance) are highly varying.
Analysis and interpretation:
Figure 1: Thermal conductivity of diamond and graphite from Rand, David. (2018)
Analysis and interpretation of figure 1:
Thermal conductivity:
The thermal conductivity of diamond is much higher than of graphite’s which is depicted from figure 1.
Diamond has a value of approximately 2200 W m−1 K−1 whereas for graphite it is 150 W m−1 K−1. Due
to diamonds structure of having light carbon atoms who have strong covalent bonds to each other,
thermal vibrations transferred from one atom to another is allowed. The movement of heat is assisted
Chemistry Research Investigation 2022
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