Carbon and some of its compounds: Allotropes of carbon

6.0 Carbon and some of its compounds

6.1 Allotropes of carbon

What is an allotrope?

Examine the pictures in Figure 6.1.

Figure 6.1(a) Allotropes of carbon

Questions 6.1(a)

1. Identify any two differences between A and B.

2. If the atoms in A are identical to those in B, suggest the cause of the differences.

3. The physical properties of A and B are certainly not identical. What about their chemical properties? Explain your answer.

4. Suggest how you would show by chemical means that A and B are the same element, carbon.

An element can exist in physically different forms but in the same physical state if the arrangements of atoms in them (structure) are different. But the different forms have the same chemical properties. They are called allotropes.

Allotropes are different forms of an element that exist in the same physical state.

Graphite (A) and diamond (B) are pure natural allotropes of carbon. They look quite different. But when equal amounts are burnt, they produce the same amount of carbon (IV) oxide as the only product. This confirms that they are the same element, carbon. Table 6.1 describes the two allotropes and impure forms carbon.

Table 6.1 Different forms of carbon

Figure 6.1(b) Structures of graphite and diamond

Questions 6.1(b)

1. In what way is the structure of graphite similar to that of metals?

2. In what way does the structure of graphite differ from that of metals?

3. From the structure of graphite, suggest a reason why it is slippery.

4. From the structure, explain why graphite conducts electricity.

5. Graphite is much softer than diamond. Explain this from the structures.

6. Graphite combines the properties of giant atomic and giant molecular structures. True or false? Explain your answer.