Diamond: Diamond consists of carbon atoms arranged in a tetrahedral structure. Each carbon atom is covalently bonded to four other carbon atoms. This forms a rigid, three-dimensional network. The bonds are covalent, meaning the atoms share electrons. The strong covalent bonds between the carbon atoms are responsible for diamond's exceptional hardness and high melting point. The rigidity of the tetrahedral structure also contributes to its transparency and high refractive index.

Silicon(IV) Oxide (SiO₂): Silicon(IV) oxide has a more complex structure than diamond, but it is also a giant covalent network. Each silicon atom is covalently bonded to four oxygen atoms, and each oxygen atom is covalently bonded to two silicon atoms. This results in a three-dimensional network structure. The bonds are again covalent. The strong covalent bonds between silicon and oxygen atoms contribute to SiO₂'s hardness and high melting point. However, the structure is not as rigidly defined as diamond's, which is why SiO₂ is more brittle than diamond. The covalent bonds also contribute to its chemical inertness.

The covalent bonds in both materials are the key factor determining their properties. The strong, directional nature of covalent bonds leads to the formation of rigid, three-dimensional networks, resulting in high hardness and high melting points. The specific arrangement of atoms (tetrahedral in diamond, more complex in SiO₂) influences the overall properties, such as transparency and brittleness.

The strong covalent bonds between carbon atoms in diamond create a very rigid and hard structure. Each carbon atom is strongly bonded to four others in a tetrahedral arrangement, resulting in a strong, three-dimensional network. This exceptional strength and hardness are crucial for its use in cutting tools.

When a diamond cutting tool is used, the hardness of the material allows it to resist deformation and wear as it applies pressure to the material being cut. The strong covalent bonds also mean that the tool can effectively shear the material being cut, separating it into smaller pieces. The high melting point of diamond also ensures it maintains its strength at high temperatures generated during cutting.

Key points:

• Hardness: Strong covalent bonds create a rigid structure.
• Strength: Three-dimensional network resists deformation.
• High melting point: Maintains strength at high temperatures.

Graphite: Graphite consists of layers of carbon atoms arranged in a hexagonal lattice. Within each layer, each carbon atom is covalently bonded to three other carbon atoms in a trigonal planar arrangement. This leaves one hydrogen-like bond, which is responsible for the layers being easily delocalised and sliding past each other. The layers themselves are held together by weak Van der Waals forces.

Diamond: Diamond also consists of carbon atoms, but the carbon atoms are arranged in a three-dimensional tetrahedral lattice. Each carbon atom is covalently bonded to four other carbon atoms. This strong, three-dimensional network of covalent bonds gives diamond its exceptional hardness and high melting point.

Comparison:

• Bonding: Both materials have strong covalent bonds. Diamond has a 3D network, while graphite has a layered structure.
• Strength: Diamond is much harder than graphite due to its strong 3D network.
• Conductivity: Graphite is a good conductor of electricity due to the delocalised electrons within the layers. Diamond is a poor conductor of electricity because all electrons are involved in bonding.
• Melting Point: Diamond has a very high melting point due to the strong covalent bonds. Graphite has a lower melting point.