Covalent compounds are generally poor conductors of electricity and have low melting points, yet graphite — a covalent form of carbon — conducts electricity well. Explain why most covalent carbon compounds have low melting points, and then account for why graphite is an exception despite being made entirely of covalent bonds.
Generated by claude-sonnet-4-6 · 2026-06-26 01:12 · grounding rag
Model Answer
Low melting points of covalent compounds: In covalent compounds, electrons are shared between atoms, forming strong bonds within molecules. However, the inter-molecular forces between molecules are weak. Therefore, little energy is needed to separate the molecules, resulting in low melting and boiling points.
Why graphite is an exception: In graphite, each carbon atom is bonded to three other carbon atoms in the same plane, forming hexagonal layers. One bond is a double bond. These layers are stacked one above the other. The remaining electrons are free to move between the layers, allowing graphite to conduct electricity well, unlike typical covalent compounds.
Source: Chapter 4 – Bonding in Carbon (Covalent Bond); Allotropes of Carbon (More to Know)
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Explanation
- Key distinction: Examiners want you to separate intra-molecular bonds (strong, within the molecule) from inter-molecular forces (weak, between molecules) — this is the textbook reason for low melting points.
- Graphite exception: The textbook only states graphite conducts electricity due to its layered hexagonal structure with a double bond. At Class 10 level, you are not required to explain "delocalised electrons" explicitly — but noting free/mobile electrons between layers earns the mark.
- Stick to source passages: Do not add extra detail (e.g., specific band theory) that goes beyond the textbook.
- Aim: ~2 marks for covalent low melting point explanation + ~1 mark for graphite exception.