The World of Metals and Non-metals

Why This Matters

Look around you right now. A spoon. A key. The wires behind the switch. A coin in your pocket. A pair of scissors. A cooking pan in the kitchen.

Most of these are made of metal. But why? Why is a spoon made of steel and not of wood? Why are cooking pans made of metal but their handles often are not? Why do electric wires use copper inside, but a rubber cover outside?

None of this is by accident. People chose each material on purpose. They picked it because of the way that material behaves.

There is a nice story in your textbook about this. Two students, Yashwant and Anandi, visit a village ironsmith named Sudarshan uncle. He makes daily things from iron — tawas (flat pans), buckets, tongs, spades, and axes. He heats a block of iron until it is red hot, then beats it with a hammer to shape it. Anandi is amazed. A solid piece of iron can be flattened and shaped! Can you do that with a piece of coal? No, coal would just break.

That difference is the heart of this chapter. By the end, you will understand what makes metals special, how non-metals are different, and why we choose the materials we do. And you will never look at a spoon the same way again.

The Big Idea

Around us, materials fall into two big families: metals and non-metals. Metals (like iron, copper, gold) usually shine, are hard, can be beaten into sheets, can be pulled into wires, ring like a bell when struck, and let heat and electricity pass through them easily. Non-metals (like coal, sulfur, oxygen) usually do the opposite — they are dull, soft or breakable, and do not carry heat or electricity well. We don’t memorise this as a list of facts. Each property has a reason, and each property decides a use. The right material for a job is simply the one whose properties fit that job.

Let’s Break It Down

What are metals and non-metals?

Let us start simply. The world is made of stuff. Scientists call this stuff matter. Some kinds of matter behave in one common way, and we call them metals. Other kinds behave very differently, and we call them non-metals.

A metal is a material that is usually shiny, hard, and lets heat and electricity flow through it. Iron, copper, aluminium, gold, and silver are metals. The spoon, the key, and the coin are all metals.

A non-metal is a material that usually does not shine and does not let heat and electricity flow easily. Coal, sulfur, oxygen, and carbon are non-metals.

Here is one important point. Metals and non-metals are special kinds of elements. An element is a pure substance that cannot be broken down into anything simpler. There are 118 known elements, and they are the basic building blocks of everything. Now, things like plastic, glass, wood, rubber, and paper are not elements. So we do not call them metals or non-metals at all. They are just other materials. Keep this in mind — it stops a lot of confusion later.

How do we tell metals and non-metals apart? We look at their properties. A property is just a quality or behaviour of a material — like “shiny”, “hard”, or “breaks easily”. Let us go through the main properties of metals one by one. Figure 4.1 below shows all six together so you have the full picture before we begin.

Tap to zoom

Property 1 — Lustre (the shine)

Lustre means shine. When something has lustre, it looks bright and reflects light. A fresh coin, a steel spoon, and a gold ring all have a shiny surface. This special shine of metals is called metallic lustre.

A tiny example: rub a coin clean with a cloth. See how it catches the light? That brightness is lustre.

Non-metals are usually dull. Dull means no shine. A piece of coal looks dark and flat. A lump of sulfur looks dull yellow. They do not sparkle the way a metal does.

One careful note: metals can lose their shine over time. An old iron nail looks dull and brownish, and an old silver ring looks black. That is not because the metal was never shiny. It is because the air slowly spoiled the surface. Scrub it clean and the shine comes back. We will see why this happens later in the chapter.

Property 2 — Hardness

Hardness means a material is firm and hard to scratch, dent, or cut. Most metals are hard. You cannot dent an iron rod with your finger.

Non-metals are usually soft (you can scratch them easily) or brittle (they crack and break).

But be careful here — “most” is not “all”. Some metals are actually soft. Sodium and potassium are metals so soft you can cut them with a knife, like cutting a bar of soap. And one metal, mercury, is even a liquid at room temperature. You may have seen it in an old thermometer. So hardness is the usual rule for metals, not a strict rule for every single one.

Property 3 — Malleability (can be beaten into sheets)

This is the property that amazed Anandi at the ironsmith’s shop. Malleability means a material can be beaten or hammered into a thin flat sheet without breaking.

A tiny example: silver foil on a sweet (the shiny chaandi ka varak on a barfi), and the aluminium foil used to wrap rotis. Both are made by hammering or rolling metal into very thin sheets. Gold and silver are the most malleable metals of all.

Now hit a piece of coal with a hammer. It does not flatten. It shatters into pieces. A material that breaks like this is called brittle. Coal and sulfur are brittle. (Wood is neither — it does not flatten into a sheet, and it does not shatter into pieces.)

Figure 4.2 below shows this difference clearly. Same hammer, completely different result.

Tap to zoom

Property 4 — Ductility (can be drawn into wires)

Where do you see metal wires? In electrical fittings, in bangles and necklaces, and inside musical instruments like the sitar, veena, and guitar. All of these need long thin wires of metal.

Ductility means a material can be drawn out (pulled and stretched) into a thin wire. Metals are ductile. Copper and aluminium are pulled into the wires we use every day.

How far can this go? Gold is so ductile that just one gram of gold can be drawn into a wire two kilometres long! That is longer than a long walk to school, all from a tiny bit of gold.

Have you ever seen a wire made of coal or sulfur? Of course not. Non-metals are not ductile. If you tried to stretch them, they would just snap.

Property 5 — Conduction of heat

Why are cooking pans made of metal? Let us find out with a simple test.

Put a metal spoon and a wooden spoon into a glass of hot water. Wait a few minutes. Now touch the top of each spoon (the part above the water). The metal spoon feels hot. The wooden spoon stays cool.

What happened? The heat from the water travelled up through the metal spoon and reached your finger. This passing of heat through a material is called conduction. A material that lets heat pass through it is a good conductor of heat.

Metals are good conductors of heat. Wood is a poor conductor — it blocks heat, so the top of the wooden spoon stayed cool.

Now you can see the clever design of a cooking pan. The pan itself is metal, so heat passes quickly from the flame into the food. But the handle is wood or plastic — a poor conductor — so the heat does not travel into your hand and burn you. The metal does the cooking; the handle keeps you safe.

Property 6 — Conduction of electricity

Have you watched an electrician? They use a screwdriver with a plastic handle, and they wear rubber gloves and shoes. Why?

We can find out by building a simple test circuit (like a tester) and placing different materials in the gap. If the bulb glows, electricity passed through the material. If the bulb stays dark, it did not.

When you try this, the bulb glows for aluminium, iron, and copper. It stays dark for sulfur, coal, wood, stone, rubber, and nylon. Do you see the pattern? Only the metals make the bulb glow.

A material that lets electricity flow through it easily is a good conductor of electricity. A material that stops electricity is a poor conductor of electricity. Metals are good conductors. Most non-metals (and materials like rubber and plastic) are poor conductors.

Now the electrician makes sense. The metal screwdriver could carry electricity into the hand and give a shock. So the handle is made of plastic, and the gloves of rubber — both poor conductors. They block the electricity and keep the electrician safe.

Property 7 — Sonorousness (the ringing sound)

Drop a metal coin on the floor. You hear a clear cling — a ringing sound. Now drop a piece of wood or coal. You hear only a dull thud.

Sonorousness means a material makes a clear ringing sound when you strike it. Metals are sonorous. This is why a school bell, the ghungroos on a dancer’s feet, and a temple bell are all made of metal. They need to ring clearly so people can hear them.

Non-metals are not sonorous. They give a dull, flat sound — no ring.

Properties of non-metals

We have seen what metals do. Non-metals mostly do the opposite. Let us gather it together.

Non-metals (like coal/carbon, sulfur, and gases like oxygen and nitrogen) are usually:

• dull, not shiny;
• soft or brittle — they break instead of bending;
• not malleable — they shatter when hammered, they do not form sheets;
• not ductile — they cannot be drawn into wires;
• not sonorous — they give a dull thud, not a ring;
• poor conductors of both heat and electricity.

Some non-metals are even gases, like oxygen and nitrogen, which float in the air. You cannot hammer a gas at all!

One special non-metal worth knowing is phosphorus. It catches fire when it touches the air. So it is stored under water to keep it safe — the exact opposite of the metal sodium, which catches fire in water and so is stored in kerosene. Different materials need very different care.

Comparing metals and non-metals

Let us put the two families side by side so the differences are easy to remember. The table below lines up each property for metals and non-metals.

Figure 4.3 below shows the same comparison as a picture, so you can take in both families at one glance.

Tap to zoom

Keep that word “generally” in mind. Metals are generally hard, generally shiny, generally good conductors. There are a few odd ones (soft sodium, liquid mercury). These exceptions do not break the idea — they just remind us nature is not always tidy.

How metals behave in air and water — rusting and corrosion

So far we looked at how metals look and feel. Now let us see how they change when they sit in air and water.

You have surely seen this. Leave an iron gate or a cycle chain out in the open for a few days, and a brown layer forms on it. This brown layer is called rust, and the process is called rusting.

But what exactly causes rust? Is it the air? The water? Both? A neat experiment answers this. Take three clean iron nails:

• Bottle A — a dry nail with a drying agent (silica gel) sealed inside. There is air, but no water.
• Bottle B — a nail fully under boiled water with a layer of oil on top to keep air out. There is water, but no air.
• Bottle C — a nail half in water, left open to the air. There is both air and water.

After about a week, only the nail in Bottle C has rusted. Figure 4.4 below shows all three.

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So the answer is clear: iron needs both air and water to rust. Just air alone, or just water alone, will not do it. This is why iron rusts faster in damp, rainy weather — there is plenty of moist air around.

Iron is not the only metal that changes in air. Copper slowly grows a green coating, and silver grows a black one. The general name for this slow spoiling of a metal’s surface by air, water, or other things is corrosion. Rusting is just the special name for the corrosion of iron.

Rusting is a real and costly problem. Every year a huge amount of money is spent repairing rusted bridges, gates, and machines. We slow it down by painting, oiling, greasing, or coating the iron with a layer of zinc (this last one is called galvanisation). All of these tricks work the same way — they keep air and water away from the iron’s surface.

A wonder of old India: the Iron Pillar of Delhi was made over 1600 years ago, in the time of Chandragupta II. It is about 8 metres tall and weighs more than 6000 kilograms. Even after all those centuries of rain and wind, it has barely any rust. The ancient Indians knew a way to make rust-resistant iron — amazing skill for that time.

There is one more difference worth knowing. When a metal like magnesium burns in air, it forms a powder (an oxide) that is basic in nature. When a non-metal like sulfur burns in air, the gas it forms dissolves in water to give an acid. So metal oxides are usually basic, and non-metal oxides are usually acidic. (You met acids and bases in an earlier chapter — they are simply opposite kinds of substances.)

Choosing the right material for a job

Now comes the part that ties everything together. Once you know a material’s properties, you can pick the right material for any job. The job needs a certain quality, and you choose the material that has that quality.

Look at Figure 4.5 below. It matches a few materials to the jobs they are best for, and tells you why each one fits.

Tap to zoom

Let us practise this thinking on a real problem.

Before we go on, let us quickly refresh one idea this chapter keeps leaning on, so nothing feels like a leap.

Now a quick “why” check to make sure the reasoning has stuck.

Common Mistakes

These are the slip-ups students make most often. Read each one — spotting the trap now means you will not fall into it in the exam.

Quick Check

Test yourself with these. Pick an answer, then read why it is right.

Practice Problems

Try each one yourself first. Then tap to check the full answer.

Easy

Medium

Challenge

Summary

You should now be able to explain each of these in your own words:

• The world’s materials sort into two families — metals (like iron, copper, gold) and non-metals (like coal, sulfur, oxygen). Both are kinds of elements; plastic, glass, and wood are neither.
• Metals are usually lustrous (shiny), hard, malleable (beaten into sheets), and ductile (drawn into wires).
• Metals are sonorous (they ring when struck) and are good conductors of both heat and electricity.
• Non-metals are usually the opposite — dull, brittle or soft, not malleable, not ductile, not sonorous, and poor conductors.
• The word “generally” matters: a few metals are exceptions (soft sodium, liquid mercury).
• Iron rusts when it meets both air and water together; the slow spoiling of any metal surface is called corrosion. We slow it with paint, oil, grease, or a zinc coating.
• Metal oxides are usually basic; non-metal oxides are usually acidic.
• We choose a material by its properties — a property decides a use. Copper for wires (conducts electricity), iron for tools (hard and strong), aluminium for pans (conducts heat), rubber for covers (poor conductor, keeps us safe).

What’s Next

In this chapter, you saw iron change colour when it rusted, and magnesium turn into a white powder when it burned. These are changes in materials — and there are different kinds of change.

Next, in Chapter 5 — Changes Around Us: Physical and Chemical, you will learn the big difference between a physical change (like ice melting into water, which you can reverse) and a chemical change (like iron rusting or magnesium burning, where a brand-new substance forms). You will be able to look at any change around you and say which kind it is. See you there!