Which one of the following statements about diamond and graphite is not correct?
Both physical and chemical properties of diamond and graphite are different
Understanding Diamond and Graphite Properties
Diamond and graphite are two well-known forms of the element carbon. They are called allotropes, meaning they are different structural modifications of the same element. Despite being made of only carbon atoms, their physical properties are vastly different due to how the carbon atoms are bonded together. However, their chemical properties, which relate to how they react with other substances, are essentially the same because they are both pure carbon.
Physical and Chemical Properties of Allotropes
When studying allotropes like diamond and graphite, it is crucial to distinguish between physical and chemical properties:
- Physical Properties: These are characteristics that can be observed or measured without changing the substance's chemical identity. Examples include hardness, density, melting point, electrical conductivity, structure, and appearance.
- Chemical Properties: These describe a substance's ability to undergo a specific chemical change or reaction. For example, how it reacts with oxygen, acids, or bases, or its flammability. Since both diamond and graphite are pure carbon, they will undergo the same chemical reactions, although the rates might differ under specific conditions due to structural differences affecting reactivity.
| Property | Diamond | Graphite |
|---|---|---|
| Structure | Tetrahedral 3D network | Hexagonal planar layers |
| Hardness | Extremely hard (Hardest known natural material) | Soft, flaky |
| Electrical Conductivity | Poor conductor (Insulator) | Good conductor |
| Density | High ($\text{approx } 3.5 \text{ g/cm}^3$) | Lower ($\text{approx } 2.2 \text{ g/cm}^3$) |
| Chemical Composition | Pure Carbon ($\text{C}$) | Pure Carbon ($\text{C}$) |
| Chemical Reactivity | Essentially the same as carbon (e.g., burns in air to form $\text{CO}_2$) | Essentially the same as carbon (e.g., burns in air to form $\text{CO}_2$) |
Analyzing the Statements about Diamond and Graphite
Let's examine each statement provided:
- Statement 1: Diamond has a tetrahedral structure, whereas graphite has a hexagonal planar structure.
This statement accurately describes the crystal structures of diamond and graphite. In diamond, each carbon atom is bonded to four other carbon atoms in a tetrahedral arrangement, forming a rigid 3D network. In graphite, carbon atoms are arranged in hexagonal rings in layers, with weak forces between the layers. Thus, this statement is correct.
- Statement 2: Both physical and chemical properties of diamond and graphite are different.
As discussed, diamond and graphite have very different physical properties (hardness, conductivity, density, etc.) due to their distinct structures. However, they are both made of the same element, carbon, and therefore exhibit the same fundamental chemical properties. For instance, both will react with oxygen at high temperatures to form carbon dioxide ($\text{CO}_2$). The statement claims that both physical and chemical properties are different, which is incorrect because their chemical properties are essentially the same. Thus, this statement is not correct.
- Statement 3: Graphite is soft but diamond is hard.
This is a well-known difference in their physical properties. The strong, rigid 3D network structure of diamond makes it extremely hard, while the layered structure of graphite, where layers can slide over each other, makes it soft and useful as a lubricant. Thus, this statement is correct.
- Statement 4: Graphite is a good conductor of electricity while diamond is not.
In graphite's structure, each carbon atom is bonded to three others in the plane, leaving one delocalized electron per atom that can move freely, making graphite a good electrical conductor. In diamond, each carbon atom is bonded to four others, with all valence electrons involved in strong covalent bonds, making it a poor conductor of electricity (an insulator). Thus, this statement is correct.
Conclusion on Diamond and Graphite Properties
The question asks which statement is not correct. Based on our analysis, Statement 2 incorrectly claims that both physical and chemical properties of diamond and graphite are different. While their physical properties are different, their chemical properties are the same because they are both pure carbon.
Revision Table: Diamond vs Graphite Key Points
| Property Type | Aspect | Diamond | Graphite |
|---|---|---|---|
| Physical Properties (Different) | Structure | Tetrahedral Network | Layered Hexagonal |
| Hardness | Very High | Low (Soft) | |
| Conductivity | Poor (Insulator) | Good (Conductor) | |
| Appearance | Transparent/Lustrous | Opaque/Dull/Grey | |
| Chemical Properties (Same) | Reactivity | Burns in $\text{O}_2$ ($\rightarrow \text{CO}_2$) | Burns in $\text{O}_2$ ($\rightarrow \text{CO}_2$) |
Additional Information on Carbon Allotropes
Allotropes are different forms of the same element in the same physical state. Carbon exists in various allotropic forms, including crystalline structures like diamond, graphite, and fullerenes (like buckyballs), and amorphous forms like coal, charcoal, and lampblack.
The significant differences in physical properties between allotropes like diamond and graphite arise purely from the differences in their atomic arrangements and bonding. Diamond's rigid, 3D network of strong covalent bonds makes it hard, dense, and a poor conductor. Graphite's layered structure with strong covalent bonds within layers but weak van der Waals forces between layers results in its softness, lower density, and conductivity due to delocalized electrons.
Understanding the concept of allotropy helps explain why elements can exist in different forms with distinct physical characteristics while retaining the same chemical identity.
Important Questions from Organic Chemistry
Which of the hydrocarbons are arranged as per the increasing order of their boiling points?
Which one of the following statements is NOT correct?
Which among the following statements with respect to carbon is/are correct?
1. Carbon forms the basis for all living organisms and many things we use
2. Carbon shows tetra-valency and the property of catenation
3. Carbon forms covalent bonds with itself and other elements
4. Carbon forms compounds containing triple and tetra bonds between carbon atoms
Select the correct answer using the code given below:
Which one of the following cell organelles does NOT possess nucleic acid?
Which one of the following is NOT a synthetic detergent?
