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Materials: Metals and Non-Metals

CBSE Class 8 Science • Chapter 3 • Detailed Master Notes

Chapter Overview

Everything around us is made of different elements. In this chapter, we will classify them broadly into Metals and Non-Metals by comparing their observable physical properties (malleability, ductility, etc.) and their chemical reactions with air, water, acids, and bases.

3.1 Physical Properties of Metals & Non-Metals

The easiest way to group materials is by observing their physical properties. While metals reflect the typical characteristics of heavy, shiny, strong materials, non-metals act as their exact opposite.

Property	Metals	Non-Metals
Physical State at Room Temp.	Most are solid. (Exception: Mercury is liquid at room temperature).	Can exist as solid (Carbon), liquid (Bromine), or gas (Oxygen, Nitrogen).
Malleability	Malleable. Can be beaten into extremely thin sheets. (e.g., Aluminum foil, Silver foil on sweets).	Non-malleable (Brittle). They break down into a powdery mass when tapped with a hammer.
Ductility	Ductile. Can be drawn/stretched into thin wires. (e.g., Copper wire, Gold wire).	Non-ductile. Cannot be drawn into wires. They snap easily.
Sonorous	Sonorous. Produce a ringing sound when struck hard on a solid surface (e.g., Temple bells).	Non-sonorous. Do not produce a ringing sound.
Conductivity (Heat/Electric)	Good conductors of heat and electricity. (e.g., Silver is the best conductor).	Poor conductors (Insulators). (Exception: Graphite, a form of Carbon, conducts electricity perfectly).
Lustre / Appearance	Have a shiny, reflective appearance (Metallic Lustre).	Dull in appearance. (Exception: Iodine, and Diamond are extremely lustrous).
Hardness	Generally very hard and strong. (Exceptions: Sodium and Potassium are so soft they can be cut with a knife).	Generally soft. (Exception: Diamond, a form of carbon, is the hardest naturally occurring substance on Earth).

Physical states of Metals and Non-metals

AI Image Prompt: A hyper-realistic, stunning still-life studio photograph showcasing the contrasts of elements on a clean white background. On the left side: a bright, shiny gold bar flawlessly cast, and a pool of liquid silvery mercury in a clear glass petri dish (Metals). On the right side: bright yellow, dull powdery sulphur piled up roughly, and a large chunk of very shiny, dark graphite (Non-Metals). Clean cinematic studio lighting reflecting beautifully off the metallic surfaces.

Topic Practice: Physical Properties

Q1. Why are electric wires typically made of copper or aluminium, while the handles of screwdrivers are made of plastic or wood?

Ans: Copper and aluminium are metals and are excellent conductors of electricity, easily letting current flow through wires. Plastic and wood are non-metals and act as insulators (poor conductors), protecting the user from electric shocks while holding the handle.

Q2. Name the metal which exists in liquid state at room temperature.

Ans: Mercury (used in traditional thermometers).

Q3. What property makes gold highly suitable for making extremely elaborate jewellery structures?

Ans: Gold is extremely malleable (can be beaten into thin shapes/foils) and highly ductile (can be drawn into fine wires), making it easy to weave and craft beautifully without snapping.

3.2 Chemical Properties

While physical properties can give us hints, testing the chemical reactions of an element is the absolute way to confirm if it is a metal or non-metal.

A. Reaction with Oxygen

Metals react with oxygen to form metallic oxides. Crucially, these metallic oxides are basic in nature.

Example: Rusting of iron.
Equation: Iron + Oxygen + Moisture (Water) → Iron oxide (Rust).
Test: When you collect the rust, dissolve it in a little water, and dip a red litmus paper into the suspension, the red litmus turns blue. This confirms it is basic. Similarly, burning a magnesium ribbon produces a white ash (Magnesium Oxide) that is also basic.
Non-metals react with oxygen to form non-metallic oxides. Crucially, these oxides are acidic in nature.

Example: Burning sulphur powder in air.
Equation: Sulphur (S) + Oxygen (O₂) → Sulphur dioxide (SO₂) gas.
Test: If you trap this gas and dissolve it in water, it forms Sulphurous acid.
Sulphur dioxide + Water → Sulphurous acid
When you dip blue litmus paper in it, the blue litmus turns red! This confirms it is acidic.

B. Reaction with Water

Some metals react violently with water, producing metal hydroxide and unleashing hydrogen gas along with massive amounts of heat (enough to catch fire).
Example: Sodium and Potassium are highly reactive. When a piece of sodium touches water, it sizzles, darts around, and catches fire. Therefore, sodium is stored safely under kerosene.
Other metals like iron react extremely slowly (rusting over months).
Non-metals generally do not react with water. However, some are incredibly reactive if just left in open air.
Example: Phosphorus is a very reactive non-metal that violently catches fire if exposed to air. To prevent this contact with atmospheric oxygen, phosphorus is stored safely under water.

AI Image Prompt: A dynamic, highly detailed action-shot of a science chemical experiment on a clean white laboratory table. A tiny piece of glowing, burning sodium metal is dancing furiously on the surface of water inside a clear, thick science beaker. Vibrant yellow-orange sparks and a small flame are exploding outward from the metal, with a thin trail of smoke rising dramatically against the pristine white background.

C. Reaction with Acids

Metals react with dilute acids to produce metal salts and liberate hydrogen gas.
The "Pop" Test: You can confirm the presence of exactly hydrogen gas by bringing a burning matchstick near the mouth of the test tube. The gas will burn instantly with a distinctive loud "pop" sound.
Non-metals generally do absolutely not react with acids.

D. Displacement Reactions

The Rule: A more reactive metal displaces a less reactive metal from its compound in an aqueous solution. A less reactive metal can never displace a more reactive one.

Example 1 (Reaction Occurs): Zinc + Copper Sulphate

Scenario: Place a zinc granule into a beaker containing a deep blue solution of Copper Sulphate ($CuSO_4$).
Result: Zinc is significantly more reactive than copper. It instantly attacks the compound, kicks copper out of the solution, and takes its place. The beautiful blue colour of the solution fades perfectly to colourless (as Zinc Sulphate forms), and a powdery red/brown mass of copper is deposited heavily at the bottom.
Zinc + Copper Sulphate (Blue) → Zinc Sulphate (Colourless) + Copper (Red-brown)

Example 2 (No Reaction Occurs): Copper + Zinc Sulphate

Scenario: Place copper turnings into a beaker containing Zinc Sulphate.
Result: Nothing happens! The solution remains unchanged because Copper is less reactive than Zinc. It does not have the "power" to displace Zinc from its compound.

AI Image Prompt: Two identical glass science beakers side by side on a bright white table illustrating a displacement reaction. The first beaker is filled with a bright, translucent deep blue liquid (Copper Sulphate) with a shiny silver zinc plate fully submerged in it. The second beaker shows the final result: the liquid is completely clear like water, and the zinc plate now sits heavily coated in a fuzzy, rusty reddish-brown copper deposit.

Topic Practice: Chemical Properties

Q1. Why is sodium stored in kerosene, but phosphorus is stored in water?

Ans: Sodium is a highly reactive metal that catches fire violently on contact with both water and air, so kerosene is the only safe liquid to submerge it in. Phosphorus, on the other hand, is a highly reactive non-metal that violently catches fire if exposed to air, but it does NOT react with water, so storing it underwater perfectly blocks the air.

Q2. What happens when a piece of iron is placed in heavily concentrated copper sulphate solution?

Ans: Since iron is more reactive strongly than copper, a displacement reaction occurs. The blue colour of the copper sulphate solution will slowly fade to pale green (iron sulphate), and a brownish-red coating of copper will deposit exactly on the iron piece.

3.3 Main Uses of Metals and Non-Metals

Uses of Metals

Metals are indispensable in building the modern world due to their strength (hardness), malleability, and high electrical conductivity.

Manufacturing transport (automobiles, aeroplanes, trains).
Building heavy machinery, satellite frameworks, and industrial gadgets.
Copper and Aluminum are extensively drawn into long wires for electrical grids.
Iron, Copper, and Aluminum are heavily used to forge cooking utensils and gigantic water boilers because they rapidly conduct heat.

Uses of Non-Metals

Non-metals, while often soft or gaseous, are literally essential for biological life and chemical industries.

Oxygen: The most crucial non-metal. It is essential for breathing and cellular respiration for absolutely all living beings.
Nitrogen: Widely used in massive quantities to manufacture strong chemical fertilisers, drastically enhancing the growth of agricultural crops.
Chlorine: A potent gas that kills bacteria, extensively used in the water purification process (municipal water plants).
Iodine: Applied directly on horrific wounds as a powerful antiseptic solution (the purple-coloured "tincture of iodine").
Sulphur and Phosphorus: Highly combustive, widely used in manufacturing explosive fireworks and festive crackers.

Final Chapter Review

Q1. State whether metallic oxides are acidic or basic. Give an example to prove it.

Ans: Metallic oxides are basic in nature. For example, when rust (iron oxide) is dissolved in water and tested, it turns red litmus paper explicitly blue, indicating it is a base.

Q2. Which non-metal is completely essential for our lives and inhaled during breathing?

Ans: Oxygen.