To classify a material, quote the properties in the table and link each to a category. A label without the evidence earns few marks.
This lesson is part of SPM Science elements and materials and reuses the reasoning from comparing elements, compounds and mixtures.
What does each property tell you?
Each property points to a structure. Conduction as a solid suggests free electrons. High melting points suggest strong forces throughout. Conduction only when dissolved suggests ions.
| Property | Suggests |
|---|---|
| Conducts as a solid | Metal |
| High melting point, conducts only when molten or dissolved | Ionic compound |
| Low melting point, never conducts | Simple covalent substance |
| Shiny and can be hammered flat | Metal |
Worked example: four invented materials
An invented table lists four materials.
| Material | Melting point (°C) | Conducts as solid | Conducts when molten |
|---|---|---|---|
| P | 1 084 | Yes | Yes |
| Q | 801 | No | Yes |
| R | 44 | No | No |
| S | 232 | Yes | Yes |
P. It conducts as a solid and has a high melting point, so it is a metal. Free electrons carry charge.
Q. It does not conduct as a solid but does when molten, and its melting point is high, so it is an ionic compound. Its ions move only when free.
R. The melting point of 44 °C is low and it never conducts, so it is a simple covalent substance.
S. It conducts as a solid and as a liquid, so it is a metal, with a lower melting point than P.
The mistake that costs marks
The slip is to repeat the label as the reason. A student writes, “Q is ionic because it is an ionic compound.”
| Reason | Type | Mark |
|---|---|---|
| Q is ionic because it is an ionic compound | Repeats the label | No mark |
| Q has a melting point of 801 °C and conducts only when molten | Quotes data | One mark |
| Q conducts when molten because its ions are free to move | Quotes data and explains | Full marks |
Put a number or an observation from the table inside every reason.
Check yourself
Material T melts at 1 535 °C, is shiny and conducts as a solid. Material U melts at −7 °C and does not conduct. Classify both with a reason.
Answer
T is a metal: it conducts as a solid, is shiny, and has a high melting point of 1 535 °C.
U is a simple covalent substance: its melting point of −7 °C is low and it does not conduct.
What to study next
Test the whole topic with the elements and materials practice set. The graph and evidence comparison lab gives more property data to classify, and the mistake log tracks repeated slips.
If you want a teacher to check your reasons with you, see online one-to-one Science tuition.