Study Module & Revision Notes
Overview: This chapter helps learners understand the basic physical and chemical differences between metals and non-metals. You will explore how metals behave in the presence of air, water and acids, recognise non-metals by their properties, and learn why metals like iron corrode (rust) while others do not.
1. What are metals and non-metals?
Metals are elements that usually have a shiny appearance (lustre), can be flattened into sheets (malleable), can be drawn into wires (ductile), and conduct heat and electricity. Examples include iron, copper, gold, aluminium and sodium. Non-metals are elements that lack metal-like properties: many are dull, brittle (if solid), poor conductors of heat and electricity, and do not show malleability or ductility. Examples: carbon (as coal), sulfur, oxygen, chlorine.
2. Physical properties — quick checklist (memorise!)
Common metallic properties
- Lustre: shiny surface that reflects light.
- Malleability: ability to be hammered into thin sheets (e.g., aluminium foil).
- Ductility: ability to be drawn into wires (e.g., copper wires in electrical cables).
- Conductivity: good conductor of heat and electricity (why metals are used for vessels and wires).
- Sonorous: metals produce a ringing sound when struck.
Common non-metallic properties
- Appearance: usually dull (though some, like iodine, are shiny in crystals).
- Brittle: solids break or shatter when beaten (e.g., phosphorus).
- Poor conductors: do not conduct heat or electricity well (e.g., sulfur).
- Non-sonorous: do not produce a ringing sound.
3. Chemical properties — how metals and non-metals react
Metals generally react by losing electrons and forming positive ions. Non-metals gain electrons to form negative ions in reactions with metals. The chapter emphasises three important chemical behaviours:
- Reaction with oxygen (burning or slow oxidation): Metals like magnesium burn in air with a bright flame, forming metal oxides. Non-metals like sulfur also burn to form non-metal oxides.
- Reaction with water: Some metals like sodium and potassium react vigorously with water to produce hydroxides and hydrogen gas. Others, like sodium, are highly reactive; many metals such as copper do not react with cold water.
- Reaction with acids: Many metals react with dilute acids to produce a salt and hydrogen gas (e.g., zinc + dilute HCl → zinc chloride + hydrogen).
- Drop a piece of copper into dilute nitric acid — no hydrogen forms but a green solution may be produced because copper reacts differently with nitric acid (an oxidising acid).
- Place a strip of magnesium in air and heat it — you will see bright white light and a white ash (magnesium oxide).
4. Reactivity series — concept explained simply
The reactivity series arranges metals from most reactive to least reactive. Highly reactive metals react with water and acids, whereas less reactive metals do not. You don’t need to memorise a long list for CBSE Class 7 — just understand that metals like potassium, sodium, and calcium are very reactive, while copper, silver and gold are much less reactive.
5. Corrosion — rusting of iron
Corrosion is the gradual destruction of metals due to a chemical reaction with their environment. The most common example is the rusting of iron. Rusting requires three things: iron, oxygen and water. Salt or acidic water speeds up rusting because they increase the flow of electrons (electrolyte action).
Equation (conceptual): iron + oxygen + water → hydrated iron(III) oxide (rust)
How to prevent rusting (short methods you must remember)
- Painting: a layer of paint prevents air and water from reaching iron.
- Oiling and greasing: used for machine parts to keep moisture away.
- Galvanisation: coating iron with zinc — zinc acts as a sacrificial metal and prevents iron from rusting.
- Alloying: mixing iron with chromium (as in stainless steel) reduces corrosion.
6. Alloys and their importance
An alloy is a mixture of two or more elements, where at least one is metal. Alloys often have improved properties — for example, steel (iron + carbon) is stronger than pure iron. Bronze (copper + tin) and brass (copper + zinc) are other common alloys. CBSE questions may ask for examples and uses — memorise a few useful ones.
7. Uses of metals and non-metals (everyday examples)
- Metals: copper for electrical wires, aluminium for cooking utensils and aircraft parts, iron for construction, gold and silver for jewellery.
- Non-metals: oxygen for breathing, nitrogen in fertilisers, carbon in pencils (graphite), sulfur for making sulphuric acid and matches.
8. Quick revision — Definitions and key terms
- Ore: a rock from which metals can be extracted.
- Alloy: a mixture of metals or metal + non-metal to improve properties.
- Corrosion: slow chemical deterioration of metals by environment.
- Native metals: metals found in free state (e.g., gold in riverbeds).
9. Exam tips & short-answer strategy
For CBSE Class 7 answers, be concise and include the keyword asked in the question (for example: 'malleable', 'ductile', 'oxidation', 'rusting'). Use bullet points for properties and steps for experiments. In definitions, keep sentences short and include an example. For numerical or observational questions (rare in this chapter), describe the experiment step-by-step and conclude with the observation.
10. Sample short questions (practice)
Q1: Define an alloy and give two examples.
Ans: An alloy is a mixture of two or more elements where at least one is a metal. Examples: steel (iron + carbon), brass (copper + zinc).
Q2: What are the conditions required for rusting of iron?
Ans: Iron, oxygen and water. Presence of salt speeds up rusting.
Q3: List three physical properties of metals.
Ans: Lustre, malleability, conductivity.