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One Element, Many Faces
Allotropy means the same element exists in different physical forms because its atoms are joined in different patterns. Carbon is the star example. The crystalline allotropes are diamond, graphite, fullerenes, graphene and nanotubes. Coal, coke, charcoal and lampblack are called amorphous forms because they have no neat long-range pattern; they are really tiny, impure bits of graphite-like structure.
How do we know they are all just carbon? Burn any of them in plenty of oxygen and the only product is carbon dioxide, and the same mass of each gives the same mass of the gas. Lavoisier-style experiments with diamond proved this.
So the chemistry never changes; only the geometry does. Exams love to ask which property comes from which geometry, so the next cards tie every property to bonding.
Worked example: a diamond ring and a pencil core look nothing alike, yet 12 g of either burns to exactly 44 g of carbon dioxide.
1. Which allotrope of carbon conducts electricity?
2. How many carbon atoms are present in one molecule of buckminsterfullerene?
3. Graphite is soft and slippery because
4. Which observation best shows that diamond and graphite are both made only of carbon?
5. Graphene is best described as
6. The 'lead' in a pencil is actually
7. A teacher asks why diamond does not conduct electricity although graphite does. Which answer is correct?
8. Which of the following is an amorphous form of carbon?