Problem 62 - General Chemistry: Principles and Modern Applications

Question

Diamond is often used as a cutting medium in glass cutters. What property of diamond makes this possible? Could graphite function as well?

Step-by-Step Solution

Answer

The hardness of diamond makes it suitable for use in a glass cutter. Graphite, on the other hand, is too soft to serve the same purpose.

Step 1: Identifying the Property of Diamond

Diamond is the hardest naturally occurring substance. It has a tetrahedral structure where each carbon atom is connected to four other carbon atoms in a 3D network making it exceptionally hard. This hardness allows it to cut through glass without getting damaged.

Step 2: Analyzing the Suitability of Graphite

Graphite, on the other hand, has a layered structure. Each layer is only weakly held to the other making graphite very soft and slippery. This softness makes it unsuitable for use in a cutting tool like a glass cutter.

Key Concepts

Tetrahedral Structure

The unique hardness of diamond is largely due to its tetrahedral structure. This structure resembles a pyramid with triangular faces, forming a three-dimensional network. In diamonds, each carbon atom forms covalent bonds with four other carbon atoms. The strength of these covalent bonds and the geometric arrangement are what make diamonds exceptionally hard. This robust framework is what allows diamonds to be used as effective cutting tools.
So, why is the tetrahedral arrangement significant? It results in even distribution of the bonding force across all directions. This uniformity ensures that any stress applied to the diamond does not easily spread or cause breakage. It's like having a tightly-knit group of friends – the more connections, the harder it is to separate them. Such structural integrity means that when a diamond is used to cut glass, it doesn’t chip or degrade.

Carbon Atom Bonding

Carbon is an incredibly versatile element due to its bonding capabilities. In the diamond's structure, each carbon atom is sp3 hybridized, meaning it forms single covalent bonds with four other carbon atoms. This type of carbon atom bonding is what leads to diamonds being the hardest and, simultaneously, one of the most stable materials found in nature.
The tetrahedral structure of diamond showcases how strong carbon bonds can achieve impressive hardness. The carbon-carbon bonds are strong due to substantial overlapping of atomic orbitals, maximizing energy stabilization. This structure isn't just about hardness. It's also about directional strength, allowing the diamond to resist external pressures from all sides.
Each carbon bond in the diamond's lattice is identical, extending the same length and involving similar energy. This ensures that the diamond maintains its strength and rigidity regardless of which way it's manipulated, making it ideal and exceptionally durable for cutting applications.

Graphite Structure

Unlike diamond, graphite boasts a completely different atomic arrangement. In graphite, carbon atoms bond in a planar structure where each carbon atom is connected to three others. This forms layers of hexagonal arrangements reminiscent of a honeycomb pattern. These sheets, however, don't have strong inter-layer bonds, resulting in a structure that easily slides, making graphite soft and slippery.
The layers of graphite are held together through weak van der Waals forces. This is contrary to the covalent bonds in diamond. These weaker forces manifest as planes that glide over one another, which is why pencils leave marks on paper easily – the layers slide off onto the paper.

• Lack of strong inter-layer bonds means graphite cannot endure the pressures needed for cutting like a diamond.
• This same feature, however, makes graphite an excellent lubricant.

While diamonds excel in strength and rigidity, graphite's structural makeup endows it with flexibility and a lubricative quality, making it unsuitable for cutting hard materials but valuable in other applications where slipperiness is needed.