Hardness
Summary: A measure of a material’s resistance to being scratched or indented. Tags: igcse chemistry keyword Created: 2026-08-06
Hardness is the property of a material that describes how resistant it is to being scratched, cut or indented. A harder material will scratch or dent a softer one. In IGCSE Chemistry, hardness is explained in terms of structure and bonding: the harder a material, the more difficult it is to force its particles apart or break its bonds.
The classic IGCSE example is diamond, the hardest natural substance. Every carbon atom in diamond forms four strong covalent bonds to four neighbouring carbon atoms, arranged in a rigid three-dimensional tetrahedral network. Because all the atoms are locked together in all directions with strong bonds, it is very difficult to break or scratch the structure, giving diamond its extreme hardness. This contrasts with graphite, where the weak forces between layers allow the layers to slide, making it soft despite also being pure carbon.
Sources
- Cambridge IGCSE Chemistry 0620 Syllabus (2023-2025), Cambridge Assessment International Education
Common Misconceptions
| Misconception | Reality |
|---|---|
| All substances with strong bonds are hard | Hardness also depends on structure; graphite has strong covalent bonds within layers but weak forces between layers, so it is soft |
| Hardness is the same as strength or density | Hardness specifically measures resistance to scratching/indentation, not how much force is needed to break the whole object |
| Diamond is hard because it is an element | It is hard because of its giant covalent tetrahedral structure with 4 strong bonds per carbon atom, not because it is an element |