The table below shows that carbon can exist as several different structures called allotropes, including graphene and lonsdaleite (a hexagonal polymorph of diamond found in meteorites).
| Allotrope | Covalent bonds per carbon atom |
|---|---|
| Graphene | .............. |
| Lonsdaleite | .............. |
| Graphite | 3 |
Complete the table to show how many covalent bonds each carbon atom forms in these allotropes.
Graphene is an exceptional conductor of electricity, while lonsdaleite is an electrical insulator. Explain this difference in conductivity. Use ideas about structure and bonding in your answer.
Buckminsterfullerene (C60C_{60}C60) has a relatively low melting point of 280∘C280^\circ\text{C}280∘C, whereas lonsdaleite has an extremely high melting point (above 3800∘C3800^\circ\text{C}3800∘C). Explain this difference in melting points. Use ideas about structure and bonding or intermolecular forces in your answer.
Explain why carbon is uniquely able to form a vast array of millions of stable, diverse organic compounds. Use ideas about the bonding of carbon in your answer.