---
title: "A student compares the scratch hardness and cleavage behavior of three crystalline solids. Cleavage is observed when a sharp blow causes a solid to split along flat, repeating surfaces.  | Solid | Approximate Mohs hardness | Observation after a sharp blow | Structural description | |—|—:|—|—| | Diamond, \\(\\text{C(s)}\\) | 10 | Flat surfaces form along certain orientations | Each \\(\\text{C}\\) atom is covalently bonded to four other \\(\\text{C}\\) atoms in a three-dimensional network. | | Quartz, \\(\\text{SiO}_2\\text{(s)}\\) | 7 | Irregular surfaces form without cleavage | Covalent \\(\\text{Si}-\\text{O}\\) bonds extend throughout a three-dimensional framework without distinct layers. | | Graphite, \\(\\text{C(s)}\\) | 1–2 | Thin, flat sheets separate readily | Strong covalent bonds connect \\(\\text{C}\\) atoms within each sheet, and London dispersion forces act between sheets. |  Which of the following best explains the hardness and cleavage results?"
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url: "https://nerd-notes.com/ubq/119393/"
date_modified: "2026-08-19T12:40:06+00:00"
---

# A student compares the scratch hardness and cleavage behavior of three crystalline solids. Cleavage is observed when a sharp blow causes a solid to split along flat, repeating surfaces.

| Solid | Approximate Mohs hardness | Observation after a sharp blow | Structural description |
|—|—:|—|—|
| Diamond, \(\text{C(s)}\) | 10 | Flat surfaces form along certain orientations | Each \(\text{C}\) atom is covalently bonded to four other \(\text{C}\) atoms in a three-dimensional network. |
| Quartz, \(\text{SiO}_2\text{(s)}\) | 7 | Irregular surfaces form without cleavage | Covalent \(\text{Si}-\text{O}\) bonds extend throughout a three-dimensional framework without distinct layers. |
| Graphite, \(\text{C(s)}\) | 1–2 | Thin, flat sheets separate readily | Strong covalent bonds connect \(\text{C}\) atoms within each sheet, and London dispersion forces act between sheets. |

Which of the following best explains the hardness and cleavage results?

A student compares the scratch hardness and cleavage behavior of three crystalline solids. Cleavage is observed when a sharp blow causes a solid to split along flat, repeating surfaces.

| Solid | Approximate Mohs hardness | Observation after a sharp blow | Structural description |
|---|---:|---|---|
| Diamond, \(\text{C(s)}\) | 10 | Flat surfaces form along certain orientations | Each \(\text{C}\) atom is covalently bonded to four other \(\text{C}\) atoms in a three-dimensional network. |
| Quartz, \(\text{SiO}_2\text{(s)}\) | 7 | Irregular surfaces form without cleavage | Covalent \(\text{Si}-\text{O}\) bonds extend throughout a three-dimensional framework without distinct layers. |
| Graphite, \(\text{C(s)}\) | 1–2 | Thin, flat sheets separate readily | Strong covalent bonds connect \(\text{C}\) atoms within each sheet, and London dispersion forces act between sheets. |

Which of the following best explains the hardness and cleavage results?

- **A.** Diamond's high hardness means that its cleavage cannot involve breaking covalent bonds; therefore, diamond must contain unrepresented molecular layers held together by weak intermolecular forces.
- **B.** Quartz's lack of cleavage means that quartz should be harder than diamond, because a solid that fractures irregularly always requires more energy to scratch than one that cleaves.
- **C.** Graphite is soft and cleaves readily because the \(\text{C}-\text{C}\) covalent bonds within each sheet are much weaker than those in diamond, so both tests separate atoms within a sheet.
- **D.** Hardness and cleavage test different responses: diamond's strong three-dimensional network resists scratching but can split along planes where fewer bonds oppose separation; quartz lacks layered weak regions, and graphite separates between sheets held by dispersion forces.

*The answer key and step-by-step explanation are available to logged-in users at https://nerd-notes.com/ubq/119393/*