Chapter 3 · Question 1

Distinguish between metals and non-metals on the basis of their physical properties. Mention at least five properties with one example or exception for each.

Answer Revealed

Direct Answer:

Metals are generally lustrous (shining), malleable (can be beaten into thin sheets), ductile (can be drawn into wires), good conductors of heat and electricity, and sonorous (produce ringing sound when struck). Non-metals lack these properties: they are non-lustrous (except iodine), non-malleable, non-ductile, poor conductors of heat and electricity (except graphite), and non-sonorous. Notable exceptions: mercury is the only liquid metal at room temperature; sodium and potassium are soft metals that can be cut with a knife; gallium and caesium have very low melting points — they melt when kept on the palm.

Simple Explanation

Metals are shiny, you can hammer them into thin sheets, pull them into wires, and they let heat and electricity flow through them easily. They also ring when you hit them — like a school bell. Non-metals are generally the opposite: dull, brittle, and bad at conducting heat or electricity. But there are some rebels: iodine is a non-metal that shines, graphite (pencil lead) is a non-metal that conducts electricity, and mercury is a metal that is a liquid, not a solid.

Exam-Ready Structure

The classification of elements into metals and non-metals is primarily based on differences in their observable physical properties. 1. Lustre (appearance): Metals have a characteristic shining surface when freshly cut or cleaned (metallic lustre). Non-metals are generally dull. Exception: Iodine (a non-metal) is lustrous. 2. Malleability: Metals can be beaten into thin sheets without breaking. Gold and silver are the most malleable metals — they can be hammered into extremely thin foils. Non-metals are brittle; they break into pieces when hammered. 3. Ductility: Metals can be drawn into thin wires. Gold is the most ductile metal — about 2 km of wire can be drawn from just 1 g of gold. Non-metals cannot be drawn into wires. 4. Hardness: Most metals are hard, but hardness varies. Sodium and potassium are soft and can be cut with a knife. Non-metals vary in hardness — diamond (a form of carbon) is the hardest known natural substance. 5. Thermal and electrical conductivity: Metals are good conductors of heat and electricity. Silver is the best conductor of heat; lead and mercury are comparatively poor conductors. Non-metals are poor conductors. Exception: Graphite (allotropic form of carbon) is a good conductor of electricity. 6. Sonority: Metals are sonorous — they produce a characteristic ringing sound when struck (school bells). Non-metals are non-sonorous. 7. Physical state: At room temperature, all metals are solids except mercury, which is a liquid. Non-metals exist as solids or gases, except bromine, which is a liquid. 8. Melting point: Most metals have high melting points. Exceptions: Gallium and caesium have very low melting points — they can melt when held in the palm. 9. Density: Metals generally have high density. Alkali metals (Li, Na, K) have low densities.

Key Points

Metals: lustrous, malleable, ductile, good conductors of heat/electricity, sonorous
Non-metals: non-lustrous, non-malleable, non-ductile, poor conductors, non-sonorous
Exceptions: Hg is the only liquid metal; iodine is a lustrous non-metal
Graphite (carbon) is a non-metal that conducts electricity
Na and K are soft metals; Ga and Cs melt if held on the palm; gold is the most malleable and ductile

Distinguish between metals and non-metals on the basis of their physical properties. Mention at least five properties with one example or exception for each.