Our world is filled with various materials, each possessing unique characteristics. Have you ever wondered why certain materials are chosen for specific purposes? For example, why are cooking pans made of one material and their handles from another? This chapter explores how we classify substances into metals and non-metals based on their observable properties and how these properties determine their everyday uses.

We begin our journey by observing the work of craftspersons, like ironsmiths, who shape metal into useful items. Their work highlights some key properties of metals, such as the ability to be hammered into different forms.

Properties Of Materials

Let's investigate some common properties that help us distinguish between different types of materials.

Malleability

Some materials can be shaped by beating them. The ability of a material to be hammered or beaten into thin sheets without breaking is called malleability.

Activity 4.1: Let Us Explore

By examining different materials like copper pieces, aluminium pieces, iron nails, coal lumps, sulfur lumps, and wood blocks, and then carefully hammering them, we can observe their response.

Metals such as copper, aluminium, and iron, when hammered, tend to flatten out into thinner shapes without breaking. This demonstrates their malleability.

In contrast, materials like coal and sulfur, when hammered, break into smaller pieces or powder. Such materials are described as brittle.

Wood also doesn't flatten or break into pieces in the same way; it has different structural properties.

S.No.	Object/Material	Appearance (Lustrous/Non-lustrous)	Hard/Soft	Effect of Hammering (Flattens/Breaks into pieces)
1.	Piece of copper	Lustrous	Hard	Flattens
2.	Piece of aluminium	Lustrous	Hard	Flattens
3.	Iron nail	Lustrous	Hard	Flattens
4.	Lump of sulfur (pea-sized)	Non-lustrous	Soft	Breaks into pieces
5.	Piece of coal	Non-lustrous	Soft	Breaks into pieces
6.	Block of wood	Non-lustrous	Hard/Soft (varies)	Does not flatten or break easily

Materials that flatten when hammered are malleable. Many metals exhibit this property. Examples include thin silver foil used on sweets and aluminium foil used for wrapping food. Gold and silver are particularly known for their high malleability.

Comparing the observations, we see that materials like copper, aluminium, and iron are generally lustrous (shiny) and hard (with exceptions like sodium and potassium being soft enough to cut with a knife, and mercury being liquid at room temperature). This metallic shine is called metallic lustre.

Materials like coal, sulfur, and wood lack this metallic lustre and are typically not as hard.

Historical Context: The ability to work with metals like copper and later iron significantly impacted human civilization, allowing for the creation of better tools, utensils, and structures. The use of iron, being stronger than copper, led to improved agricultural tools like ploughs, contributing to progress.

Ductility

Another important property related to shaping materials is ductility. This is the ability of a material to be drawn out into thin wires.

We commonly see this property in action with electrical wiring made from copper or aluminium, or metal wires used in jewellery, musical instruments like the veena or guitar, and even in stronger forms like steel ropes for suspension bridges or cranes.

Metals are generally ductile. Gold is exceptionally ductile; one gram of gold can be stretched into a wire approximately 2 kilometres long!

Materials like coal or sulfur cannot be drawn into wires, confirming they are not ductile.

Sonority

Have you noticed that certain objects make a distinct ringing sound when struck or dropped?

Activity 4.2: Let Us Investigate

Dropping objects like a metal spoon, a coin, a piece of coal, and a block of wood from the same height reveals differences in the sound produced. Metal objects produce a clear, ringing sound, while coal and wood produce duller sounds.

The property of materials that makes them produce a ringing sound is called sonority. Materials possessing this property are said to be sonorous. Metals are typically sonorous. This is why bells (like school bells or ghungroos) are made of metal to produce a clear, sustained sound.

Conduction Of Heat

Some materials transfer heat easily, while others do not.

Activity 4.3: Let Us Investigate

By placing a metal spoon and a wooden spoon of similar size into a container of hot water and observing which end gets hot first, we can compare their ability to transfer heat. The end of the metal spoon quickly becomes hot to the touch, while the wooden spoon's end remains relatively cool.

This demonstrates that heat is transferred along the metal spoon much more efficiently than along the wooden spoon. This transfer of heat through a material is called conduction. Materials that transfer heat well are called good conductors of heat.

Metals are generally good conductors of heat. This is why cooking vessels are usually made of metal – to efficiently transfer heat from the stove to the food. Materials like wood are poor conductors of heat (also called insulators), which is why they are used for making handles of cooking pans to prevent burns.

Conduction Of Electricity

Similar to heat, materials also differ in their ability to allow electric current to flow through them.

Activity 4.4: Let Us Design And Create

Using a simple electric circuit tester (like the one from the previous chapter, consisting of a cell and a lamp connected by wires with a gap), we can test different materials. By placing various objects in the gap, we observe whether the lamp lights up, indicating that electric current is flowing through the object.

S.No.	Object/Material	Prediction (Bulb glows/does not glow)	Observation (Bulb glows/does not glow)	Conclusion (Good conductor/Poor conductor)
1.	Piece of aluminium foil	Glows	Glows	Good conductor
2.	Iron nail	Glows	Glows	Good conductor
3.	Lump of sulfur (pea-sized)	Does not glow	Does not glow	Poor conductor
4.	Copper wire	Glows	Glows	Good conductor
5.	Piece of coal	Does not glow	Does not glow	Poor conductor
6.	Piece of dry wood	Does not glow	Does not glow	Poor conductor
7.	Stone	Does not glow	Does not glow	Poor conductor
8.	Eraser made of rubber	Does not glow	Does not glow	Poor conductor
9.	Piece of nylon rope	Does not glow	Does not glow	Poor conductor

Testing various materials shows that objects made of metals (like aluminium, iron, copper) allow the lamp to glow, while objects made of sulfur, coal, wood, stone, rubber, or nylon do not. This indicates that metals are generally good conductors of electricity, while the other materials tested are poor conductors of electricity (insulators).

This property explains why electrical wires are made of metal (usually copper or aluminium) and why they are covered with plastic or rubber insulation. The insulation prevents electric current from flowing to our bodies, protecting us from electric shocks. Similarly, screwdriver handles and electrician's gloves are made of insulating materials for safety.

Based on these properties – lustre, hardness, malleability, ductility, sonority, and conduction of heat and electricity – we can broadly classify many materials as metals.

Effect Of Air And Water On Metals: Iron

Metals don't always remain unchanged when exposed to the environment. Air and water can interact with them, causing changes.

A common observation is the formation of brown deposits on iron objects left outdoors. This is known as rusting.

Activity 4.5: Let Us Experiment

To investigate the conditions necessary for iron to rust, we can place clean iron nails in three different environments:

1. In a bottle with dry air (using silica gel to absorb moisture).
2. In a bottle with boiled and cooled water (to remove dissolved air), topped with a layer of oil (to prevent air from dissolving in water).
3. In a bottle with some water, exposed to normal air.

After several days, observe the iron nails in each bottle.

Glass Bottle	Presence of Water (Yes/No)	Presence of Air (Yes/No)	Observations (Rust formed?)
A (Dry air)	No	Yes	No rust
B (Water only)	Yes	No (minimal)	No rust
C (Air and water)	Yes (partial dip)	Yes	Brown deposits (Rust) formed

The experiment reveals that rust (brown deposits) forms on iron only when it is exposed to both air (oxygen) and water (moisture). Dry air alone or water alone is not sufficient for rusting.

Rusting is a form of corrosion, which is the gradual deterioration of a metal surface due to reaction with substances in the air or water.

Rusting of iron is a significant problem, causing damage to structures and objects, requiring extensive repairs or replacements.

Methods to prevent rusting include painting, oiling, greasing, or coating iron with another metal like zinc (galvanisation).

Fascinating Fact: The Iron Pillar of Delhi, over 1600 years old, shows remarkable resistance to rust, a testament to the advanced metallurgical skills in ancient India.

Effect Of Air And Water On Other Metals

Other metals also react with air, often forming metal oxides.

Activity 4.6: Let Us Investigate (Demonstration Activity)

Burning a magnesium ribbon in air produces a bright white flame and leaves behind a white powdery ash. This ash is magnesium oxide, formed by the reaction of magnesium metal with oxygen from the air.

When this magnesium oxide powder is mixed with water, the resulting solution is basic in nature. This can be confirmed by testing it with litmus paper; the solution turns red litmus paper blue.

This is a general property: oxides of metals are usually basic in nature.

Some metals are highly reactive with air and water, like sodium, which reacts vigorously and is therefore stored in kerosene to prevent contact with moisture and oxygen.

Substances That Behave Differently From Metals In Air And Water

Not all substances exhibit the properties of metals. There is another category of substances called non-metals.

Activity 4.7: Let Us Experiment (Demonstration Activity)

Burning powdered sulfur in air produces a gas, primarily sulfur dioxide. When this gas is dissolved in water, it forms sulfurous acid.

Testing the solution of sulfur dioxide in water with litmus paper shows that it is acidic; it turns blue litmus paper red.

This suggests a different behaviour compared to metal oxides. Generally, oxides of non-metals are acidic in nature.

Activity 4.8: Let Us Explore

Mixing sulfur powder with water reveals that sulfur does not react with water. This is another difference in behaviour compared to some metals.

Based on observed properties and reactivity, we classify substances that differ from metals as non-metals. Non-metals typically:

• Are non-lustrous (dull).
• Are generally soft (though some, like diamond - a form of carbon, are exceptions).
• Are brittle (break easily when hammered).
• Are not ductile (cannot be drawn into wires).
• Are not sonorous (do not produce a ringing sound).
• Are generally poor conductors of heat and electricity (though carbon in the form of graphite is a conductor of electricity).
• Form acidic oxides when they react with oxygen.
• Generally do not react with water.

Examples of non-metals include sulfur, phosphorus, oxygen, hydrogen, nitrogen, and carbon.

Important Note: Materials like plastic, glass, wood, rubber, and paper are not classified as metals or non-metals in the same way because they are compounds or mixtures, not pure elements. An element is a fundamental substance that cannot be broken down into simpler substances. Metals and non-metals are categories of elements. Currently, there are 118 known elements, some natural and some man-made.

Are Non-Metals Essential In Everyday Life?

While metals are visible and used for many tools and structures, non-metals are equally, if not more, essential for life and modern society.

• Oxygen: A non-metal absolutely vital for respiration in living organisms. It is also necessary for combustion (burning).
• Carbon: The fundamental building block of all organic matter and life forms. It's a key component of carbohydrates, proteins, fats, and DNA.
• Nitrogen: A major component of the atmosphere, essential for plant growth as a nutrient, and used in the production of fertilisers and many chemicals.
• Chlorine: Used for purifying water to make it safe for drinking.
• Iodine: Used as an antiseptic solution for treating wounds.

Thus, non-metals are indispensable for life, health, and many industrial processes.

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In a Nutshell:

• Substances are broadly classified into metals and non-metals based on their physical and chemical properties.
• Generally, metals are shiny (lustrous), hard (with exceptions), malleable (can be hammered into sheets), ductile (can be drawn into wires), sonorous (produce ringing sounds), and are good conductors of heat and electricity.
• Generally, non-metals are dull (non-lustrous), soft (with exceptions), brittle (break easily), not ductile, not sonorous, and are poor conductors of heat and electricity (with exceptions like graphite).
• Metals react with oxygen to form basic oxides.
• Non-metals react with oxygen to form acidic oxides.
• Most non-metals do not react with water.
• Metals can undergo corrosion, such as iron rusting, when exposed to air and water.
• Both metals and non-metals have numerous critical applications in everyday life, from tools and structures to biological processes and industrial uses.

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