Graphite, a form of carbon, conducts electricity like a metal, whereas sulfur — also a non-metal — is a brittle solid that does not conduct electricity at all. Yet both are classified as non-metals. (i) What does this suggest about using physical properties alone to classify elements as metals or non-metals? (ii) Which category of properties provides a more reliable basis for this classification? Justify your answer with one example.
Generated by claude-sonnet-4-6 · 2026-06-26 01:05 · grounding rag
Model Answer
(i) Physical properties alone are not reliable for classifying elements as metals or non-metals, because there are many exceptions. Graphite (a non-metal) conducts electricity like a metal, and iodine (a non-metal) is lustrous. Such exceptions show that no single physical property is universal to all metals or non-metals.
(ii) Chemical properties provide a more reliable basis for classification.
Justification: Metals form basic oxides when burnt in air, while non-metals form acidic oxides. For example, magnesium burns to form MgO, which is basic, whereas sulphur burns to form SO₂, which dissolves in water to give an acidic solution. This chemical behaviour is consistent and does not show the exceptions seen in physical properties.
Source: Chapter 3, Section 3.1.2 and Activity 3.8
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Explanation
- Part (i) expects you to state that physical properties have too many exceptions — the textbook itself lists graphite conducting electricity, iodine being lustrous, and alkali metals being very soft as key examples.
- Part (ii) is directly from the textbook conclusion after Activity 3.8: "Elements can be more clearly classified as metals and non-metals on the basis of their chemical properties." Always support with the metal oxide / non-metal oxide example (basic vs. acidic oxide) as the examiner expects it.
- Don't just say "chemical properties are better" — you must justify with an example as the question demands.