Class 7 Science Chapter 4: The World of Metals and Non-metals

The Blacksmith and the Question

Anandi watches Sudarshan at his furnace. He pulls out a block of iron, red hot, and beats it hard with a hammer. She asks why. He is shaping it into an axe. Then she asks the better question. Can every metal be beaten flat like that?

A Test You Can Run

That question can be answered with a hammer. Gather one iron nail, a lump of sulfur about the size of a pea, some coal, a wooden block, and offcuts of aluminium and copper. Look at each one first. Then hit each one on a hard surface and watch what happens.

Do It Safely

An adult or your teacher should be with you for this. A hammer and small hard pieces are a bad combination for fingers and eyes. Work on a solid surface and hit downwards, not sideways. None of the materials here is dangerous in itself.

First Look: Which Ones Shine?

Before any hammering, note the appearance. The copper, the aluminium and the iron nail all shine. The coal, the sulfur and the wood look dull. That shine has a name. The lustre shown by metals is called metallic lustre.

Hard or Soft?

Note hardness too. The copper, the aluminium and the iron are hard. The coal and the sulfur are not. So two properties have already split your six items into the same two groups, which is a good sign that the split is real.

Naming the Groups

Copper, aluminium and iron are metals. Coal, sulfur and wood are not. You have sorted them using nothing but your eyes and your fingers, before the hammer has even been picked up.

Now the Hammer

Hit each one. The copper flattens. The aluminium flattens. The iron nail flattens. The coal breaks into pieces. The sulfur breaks into pieces. The wood does neither: it just sits there, dented perhaps, but neither flat nor shattered.

Malleability

Being able to hammer a material out into thin sheet is called malleability. Most metals have it. That is why there is silver foil on sweets and aluminium foil around food. Both are made by beating metal thinner and thinner.

The Champions

No metal hammers thinner than gold, with silver just behind it of all. A very small amount of either can be beaten out into a remarkably large, thin sheet. That is exactly why the foil on a sweet is silver rather than, say, iron.

Brittle

Coal and sulfur did something different. They broke. A material that shatters when struck is called brittle. Brittle is the useful opposite of malleable, and the hammer test tells you which you have in one blow.

Wood Fails Both Tests

Wood is worth pausing on. It did not flatten and it did not shatter. So it is neither malleable nor brittle. That matters because it shows the two words are not a pair of boxes covering everything. A material can simply fail both.

Not Every Metal Is Hard

Here the neat pattern develops a crack, and the crack is the interesting part. Are all metals hard and solid? No. Sodium and potassium are metals, and both are soft enough to cut with a knife. Hardness is a tendency among metals, not a law.

A Metal That Flows

There is a stranger case. Mercury is a metal, and at room temperature it is a liquid. You may have seen it in an old thermometer. So even being solid is not something every metal manages, which is a useful warning about how we use the word generally.

Why Exceptions Are Not a Nuisance

It would be tidier if every metal were hard and solid. But a rule with known exceptions is more honest than a rule you have to pretend about. When you read that metals are hard, read it as most metals are hard, and keep sodium and mercury in mind.

Why Three Tests Rather Than One

It would be quicker to use one test, and far less reliable. Lustre can mislead, because a freshly broken non-metal can look shiny. Hardness can mislead, because sodium is soft. The hammer misleads for the same reason. Three tests agreeing is much stronger evidence than any single one, and where they disagree you have found something worth following up.

Keeping an Honest Table

Write down every result, including the awkward ones. If a sample looks shiny and then shatters, record exactly that. Do not tidy it towards the answer you expected. The rows that refuse to fit are the ones that lead you to sodium, to potassium and to mercury, and those three are the most interesting things in this topic.

What Comes Next

Lustre, hardness and malleability have taken you a long way with two eyes and a hammer. The next topic adds three more tests: whether a material can be drawn into wire, whether it rings when struck, and whether it carries heat and electricity.

Scenario:

Reema helps at a sweet shop where the barfi is covered with a silver foil so thin it tears if she breathes on it. In the kitchen behind, charcoal for the stove snaps into chips whenever a sack is dropped. That afternoon her glass bangle slips off and shatters on the floor. Her cousin says the bangle must be a metal because it broke like the charcoal did. Reema disagrees. She points out that the foil and the bangle behaved in opposite ways, and that the foil is the metal of the two. She also recalls hammering samples in class, where copper spread flat and coal broke apart.

Analysis:

Reema has the reasoning the right way round. Being beaten into very thin sheets is malleability, and that is a metal property, which is why silver can be made into foil fine enough to tear on a breath. Shattering is brittleness, and it is what coal and charcoal do. So her cousin has the test inverted: breaking is evidence against a metal, not for one. The glass bangle is brittle and is not a metal at all. One caution worth adding. Brittleness and malleability are not a complete pair, because wood is neither, so a sample that simply dents tells you less than one that flattens or shatters.

Activity:

Find three safe household items you think are metal, non-metal and neither. Without hammering anything, write down for each one whether it is lustrous and whether it is hard, then predict what a hammer would do. Say which prediction you are least sure about and why.

Title:

Sort six samples with your eyes and a hammer

Safety:

An adult must be present. Work on a solid surface, strike downwards, and keep your face well back from flying pieces.

What You Notice:

The shiny hard samples flatten, the dull ones shatter, and the wood does neither. Lustre and hardness predicted the result before you picked the hammer up, which is why those two quick tests are worth doing first.

Sodium and potassium are metals soft enough to be cut with a knife.

Mercury is a metal, yet it is liquid at room temperature, which is why it was used in thermometers.

No metal hammers thinner than gold, with silver just behind it, which is how silver foil on sweets is made so thin.

Hammer tells you: flat means malleable, shattered means brittle, unmoved means neither.

Gold and silver beat the rest: they are the two most malleable metals.

Where Do You See Metal Wire?

Look around and the answer is everywhere. Copper or aluminium wire runs through electrical fittings. Bangles, necklaces and earrings are made from metal wire. So are the strings of a veena, a sitar, a violin and a guitar. That is a lot of jobs for one shape.

Ductility

Where a material can be pulled out into wire, we call that ductility. It belongs mainly to the metals. Ask yourself whether you have ever seen a wire of coal or of sulfur. Obviously not. So coal and sulfur are not ductile.

How Far Gold Will Stretch

Gold is the champion here, and the number is worth repeating. One gram of gold can be drawn into a wire two kilometres long. A gram is about the mass of a small paperclip, and two kilometres is a long walk. That is what extreme ductility means.

Wire That Carries Weight

Ductility also gives us something strong. Steel is a mixture of a metal and a non-metal: iron and carbon. Ropes made of steel wire support very heavy loads. That is why you find them in suspension bridges and on cranes lifting heavy objects.

Now Drop Things

Try the next test with your ears. Pick up a coin, a wooden block, a lump of coal and one metal spoon, then drop each from the same height onto the floor. Be careful as you do it. Listen to the four sounds rather than watching the objects.

Ringing Against Dull

The spoon and the coin give a ringing sound. The coal and the wood give dull sounds. The difference is obvious the first time you hear it, and once you have heard it you can use it without thinking.

Sonority

When a metal answers a knock with a clear ring we call that sonority, and such metals are described as sonorous. The school bell rings because it is metal. So do ghungroos. A person who cannot see can tell wood from metal by tapping, which is sonority put to real use.

The Spoons in Hot Water

The third test uses heat. Stand a metal spoon and a wooden spoon in the same cup of hot water, for the same length of time, then touch the handles. The metal one is hot. The wooden one is barely warm, though both sat in the same water.

Conduction

Heat has travelled up the metal and not up the wood. Heat moving along a material from one place in it to another is conduction, and anything that carries heat that way is a conductor. Metals are good conductors of heat, and wood is a poor conductor.

Why a Pan Is Metal and Its Handle Is Not

Now the kitchen makes sense. Cooking vessels are metal because heat must get through the base to the food. Their handles are wood, or something else that does not conduct, because heat must not get through to your hand. One pan, two opposite requirements.

The Tester Again

For the fourth test, build the tester circuit from the electricity chapter. Collect aluminium foil, an iron nail, a pea-sized lump of sulfur, copper wire, coal, dry wood, a stone, a rubber eraser and some nylon cord. Predict which will light the bulb before you test them.

What the Bulb Says

The aluminium, the iron and the copper light it. The sulfur, the coal, the wood, the stone, the eraser and the nylon all leave it dark. Look at the first group: every single one is a metal. The pattern is as clean as the lustre test in the last topic.

The Two Names Again

Where current slips through a material without trouble, it counts as a good conductor of electricity. Where a material blocks the current and the bulb stays dark, it counts as a poor conductor. You met these words in the electricity chapter and here they turn up as a property of metals.

Why the Electrician Is Dressed Like That

Watch an electrician and two things stand out: the plastic handle on the screwdriver, and the rubber gloves and shoes. Both plastic and rubber are poor conductors of electricity, so they keep current from reaching the person holding the tool.

Five Properties, One Pattern

Put the two topics together. Metals are generally hard and lustrous, malleable and ductile, sonorous, and good conductors of heat and electricity. Non-metals are generally the reverse. The word generally is doing real work in that sentence, as sodium and mercury already showed you.

What Comes Next

All five tests so far have left the samples exactly as they were. The next topic does something different. It leaves iron in damp air for days and watches it change, which is the first time in this chapter that a metal is altered rather than merely measured.

Scenario:

Vikram uncle runs a small workshop beside a building site. A crane there lifts steel beams on a rope that looks thin for the weight it carries. Inside, Vikram notices that the electric cable to the welding machine is copper under a thick rubber sleeve, and that the welder wears rubber boots. At lunch the cook lifts an iron pan off the fire by its wooden handle without flinching, then uses a metal spoon left in the pan and drops it with a yelp. Vikram cousin says the cook was careless. Vikram thinks the pan was built correctly and the spoon was the mistake.

Analysis:

Vikram is right. Each part of the workshop shows one property from this topic. The crane rope is steel, a mixture of iron and carbon. Metals are ductile, so steel can be drawn into wire, and rope spun from steel wire carries a very heavy load. The cable is copper because metals conduct electricity well. Its rubber sleeve and the welder boots are poor conductors, so current cannot reach a person. The pan is a deliberate pairing. A metal vessel carries heat into the food; a wooden handle carries it poorly, so the cook hand is safe. The metal spoon is the one object with no insulating part. Conduction carried heat straight along it to the cook fingers. The design was sound, and the spoon defeated it.

Activity:

Find three objects at home that pair a conductor with a poor conductor in one item, such as a pan, a plug or a screwdriver. For each, write down which part carries something and which part blocks it, and say what is being carried: heat, electricity, or both.

Title:

Two spoons and a cup of hot water

Safety:

An adult must pour the hot water. Touch each handle only briefly, and keep your face away from the steam.

What You Notice:

The metal spoon handle is noticeably hot. The wooden one is barely warm. Both sat in the same water for the same time. Heat travelled along the metal and not along the wood. That is what makes one a good conductor and the other a poor one.

A single gram of gold pulls out into two kilometres of wire, which makes it the most ductile metal.

Steel is iron blended with carbon, so it combines a metal with a non-metal.

A person who cannot see can tell wood from metal by the sound a stick makes, which is sonority at work.

Draw it, drop it, heat it, wire it: ductility, sonority, heat conduction, electrical conduction.

A pan of metal with a handle of wood: one conducts because we want it to, the other because we do not.

Something Everyone Has Seen

An old gate, a nail left outside, the underside of a cycle: all of them go brown and flaky. The question is what causes it. Most people would say water. That answer is half right, and finding the other half needs an experiment with three bottles.

Three Bottles, Three Conditions

Put an iron nail in each of three glass bottles. In bottle A the nail sits in dry air, kept dry with silica gel, which absorbs moisture. In bottle B the nail sits in water alone, with a layer of oil on top to keep air out. In bottle C the nail sits in water with air above it.

Why Each Bottle Is Built That Way

The point is to allow exactly one condition at a time. Bottle A offers air without water. Bottle B offers water without air, which is what the oil layer is for. Bottle C offers both together. If you changed two things at once, the result would tell you nothing.

Leave Them and Look

After some days, examine all three nails. The nails in bottles A and B show no brown deposits at all. They look much as they did. The nail in bottle C has brown deposits on it. One bottle out of three has produced the effect.

What That Proves

Air alone does not do it. Water alone does not do it either. The presence of both water and air together is what the brown deposit needs. So moist air is responsible for the brown deposits on objects made of iron, and that is why a nail kept indoors in a dry drawer stays bright.

Naming It

We call that brown deposit rust. That deposit forming on anything made of iron is what rusting means. Keep the two words apart: rust is the stuff you can see, and rusting is what happened to produce it.

Iron Is Not Alone

Many other metals change when left out in the open. Look at an old copper vessel and you may find a green coating. Look at neglected silver and you may find a black one. The metal is being spoiled from the surface inwards in each case.

Corrosion

There is a word covering all of it. When air, water or something else eats slowly into a metal surface, that spoiling is called corrosion. So rusting is corrosion that happens to iron, and the green on copper and the black on silver are corrosion too.

Why It Is Worth Money

Rust costs this country a great deal. Huge sums go every year on putting right or replacing the iron structures it has eaten into. Bridges, railings, gates and roofing all have to be dealt with, so this is an expensive piece of chemistry.

Four Ways to Stop It

Since rusting needs moist air to reach the iron, every method of prevention keeps moist air off. Painting does it. So does oiling, and so does greasing. The fourth is laying a skin of zinc over the iron, which is what galvanisation means.

Why a Painted Gate Lasts

Now you can explain the gate in your street. While its paint is whole, moist air never touches the iron and no rust forms. Where the paint chips, a brown patch appears at exactly that spot and nowhere else. The chip has let the air in.

A Pillar That Refused

There is a famous exception. Delhi has an iron pillar raised under Chandragupta II, over sixteen centuries back. It stands about eight metres high and weighs more than six thousand kilograms. It has faced wind, rainfall and intense weather ever since.

And Barely Any Rust

Despite all those centuries, it has barely any rust. It was made in a way that resists rusting. Nobody painted it or greased it for sixteen hundred years, so the resistance is in the iron itself and in how it was worked.

What That Tells Us

This says something about the skills developed in metal technology in India. Making iron that resists rust for sixteen centuries is a serious achievement, and it was done long before anyone could have explained rusting in the terms this chapter uses.

Why Three Bottles and Not Two

You could argue that two bottles would do: one wet and one dry. They would not. Water alone and air alone are both single conditions, and you need to rule out each of them separately before the pair can be blamed. Three bottles let you say which single condition fails and which combination works, and that is the whole reason the experiment is built the way it is.

What Comes Next

Rusting is slow, and it needs water. The next topic heats metals and non-metals in air instead and watches what they turn into. The answers turn out to connect straight back to the acids and bases of chapter two.

Scenario:

Farida family and their neighbours put up identical iron gates in the same month. Her family paints theirs every second summer. The neighbours leave theirs bare because they like the look of the metal. After four monsoons the bare gate is brown and flaking and one hinge has worn thin. Farida gate is sound, except for a patch of brown below the latch where a chip of paint came off in the first year. Her brother says the paint must contain something that kills rust. Farida says the paint does nothing of the kind, and points at the patch under the latch as her evidence.

Analysis:

Farida has the mechanism right and her evidence is well chosen. Rusting needs water and air together, so moist air at the iron surface is what produces rust. Paint is one of the four named methods of prevention, alongside oiling, greasing and galvanisation with zinc, and all four work the same way: they keep moist air off the metal. Nothing in the paint attacks rust. The patch under the latch is the proof, because rust appeared at precisely the one place where the coating was missing and nowhere else. If the paint were killing rust chemically, the chipped spot would be no worse than the rest. The bare gate shows what happens with no barrier at all, and the worn hinge shows that corrosion eats into the metal rather than just marking it.

Activity:

Find an iron or steel object outdoors near you, such as a gate, a railing or a pole. Note where it is rusted and where it is not, and write one sentence for each spot explaining what made the difference. Do not touch anything sharp or flaking.

Title:

Set up your own rusting test

Safety:

Ask an adult to boil and cool the water. Handle the nails carefully, and wash your hands afterwards.

What You Notice:

Only the nail in jar C turns brown. Jars A and B differ from C in just one condition each, so the comparison points straight at the cause. Both water and air have to be present, which is why moist air is the answer.

The Iron Pillar of Delhi is about eight metres high and weighs more than six thousand kilograms.

Copper turns green and silver turns black in open air, so iron is not the only metal that corrodes.

Enormous sums are spent every year in India on replacing or repairing iron structures damaged by rust.

Rust needs BOTH: water alone will not do it, and dry air will not either.

POGZ to stop rust: Paint, Oil, Grease, or Zinc.

From Slow to Fast

Rusting took days. This topic takes seconds. Instead of leaving a metal in damp air, we will burn it, and then do the same with a non-metal. Both reactions produce something new, and the new substances turn out to answer a question from chapter two.

Watch, Do Not Hold

The magnesium experiment is a demonstration. Your teacher performs it and you watch. Wear protective eyeglasses and keep a safe distance. The flame is extremely bright, so do not stare into it. Those are the book own cautions and they are worth following exactly.

Burning Magnesium

A magnesium ribbon three or four centimetres long is cleaned with sandpaper, held in tongs, and lit from a spirit lamp or a candle. The ribbon burns with a fierce white light. When it finishes, a white powder is left, and that powder is collected on a watch glass.

What the Powder Is

The white powder is magnesium oxide. It formed from a reaction between the magnesium and oxygen out of the air. So the metal has not simply got hot and changed colour. It has combined with something from the air to make a different substance.

Now Test It

Stir the white powder into a few drops of warm water. Then test the solution with litmus, exactly as you did in chapter two. What happens? The red litmus paper turns blue. You already know what that result means.

Metal Oxides Are Basic

A sample that turns red litmus blue is basic. So the solution of magnesium oxide is basic in nature. And magnesium is not a special case: as a rule a metal oxide comes out basic. One experiment has linked this chapter to the last one.

A Metal Kept Under Oil

Some metals are far more eager than magnesium. Oxygen and water both set sodium off violently, and the reaction throws out a great deal of heat. So sodium is stored in kerosene, which keeps it away from moisture and air. Guess the nature of its oxide, and you will guess basic.

Now a Non-metal

Sulfur is burnt in a deflagrating spoon, again as a demonstration. Set sulfur alight in air and sulfur dioxide gas comes off. That gas is then dissolved in water, and the resulting solution is tested with litmus just as the magnesium oxide was.

Non-metal Oxides Are Acidic

The result is the opposite. Dissolving sulfur dioxide in water forms sulfurous acid, and the solution is acidic in nature. Generally, the oxides of non-metals are acidic. So the two groups of elements give two opposite kinds of oxide.

Sulfur and Water

There is one more test. Put some sulfur powder in a glass tumbler and add a small amount of water. Watch. Nothing happens. There is no reaction at all when sulfur is placed in water, and generally a non-metal is left alone by water.

The Opposite Storage Problem

Phosphorus is the mirror image of sodium. It catches fire when exposed to atmospheric air, so phosphorus is stored in water. Sodium hides from water under kerosene; phosphorus hides from air under water. The two dangers are opposite, so the two jars are opposite.

What Non-metals Are Like

Substances such as sulfur and phosphorus behave differently from metals with air and water. Most are soft and look dull. None hammers into sheet or pulls into wire, none rings when struck, and heat and current both pass through them badly. These are the non-metals.

More Non-metals

Sulfur and phosphorus are not the only ones. Oxygen, hydrogen, nitrogen and carbon are non-metals too. That list may surprise you, because three of those four are gases, and it shows that being a non-metal says nothing about what state a substance is in.

A Warning About Materials

Here is a mistake worth avoiding. Non-metals must not be confused with things like glass, rubber, paper, wood or plastic. Those five are not classified as metals or non-metals at all, and the reason is not that they sit somewhere in between.

Because They Are Not Elements

Both groups sit inside the wider family of elements. An element is one that nothing can split into anything simpler. Plastic, glass and wood are not elements, so the question of which group they fall into does not arise.

One Hundred and Eighteen

At present 118 elements are known. Everything there is gets built from them. Some turn up in nature, while others are made in laboratories and do not exist in nature at all. Every metal and every non-metal you meet is one of those 118.

Scenario:

A new science teacher is checking the store cupboard. She finds a jar labelled sodium sitting in a clear liquid, and a jar labelled phosphorus also sitting in a clear liquid. A label on the shelf has come loose and she cannot tell which liquid is which. There is also a jar of sulfur powder kept dry on the shelf, with no liquid at all, and a small sealed tin of magnesium ribbon. A student offers to pour a little water into the sodium jar to top it up. The teacher stops him at once and says that would be dangerous.

Analysis:

The teacher is right, and the reason is in this topic. Sodium reacts vigorously with both oxygen and water, and a great deal of heat is generated. That is exactly why it is stored under kerosene, which keeps air and moisture off it. Adding water would feed the very reaction the storage is designed to prevent. Phosphorus has the opposite problem: it catches fire when exposed to atmospheric air, so it is stored under water. So the two clear liquids can be told apart by which element they hold, since each element hides from what the other is kept in. The sulfur needs no liquid at all, because sulfur in water shows no reaction and non-metals generally do not react with water.

Activity:

Draw three labelled jars for sodium, phosphorus and sulfur. Beside each, write what it must be kept away from and which liquid, if any, does that job. Then write one sentence saying what would happen if the sodium and phosphorus jars were swapped.

Title:

Test an oxide you can make safely

Safety:

Do not use magnesium, sulfur or any reactive metal yourself. Those are demonstrations for your teacher. Wash your hands afterwards and keep the liquid away from your eyes.

What You Notice:

The red litmus turns blue and the blue stays blue, so the solution is basic. Lime comes from a metal, and this is the same result the magnesium oxide gave, which is why metal oxides are described as generally basic.

Sodium is kept under kerosene because it reacts vigorously with both oxygen and water, releasing much heat.

Phosphorus is kept under water because it catches fire on contact with ordinary air.

There are 118 known elements, and some of them do not occur in nature at all but are made in laboratories.

Metal oxide turns red litmus blue; non-metal oxide does the opposite.

Sodium hides in kerosene, phosphorus hides in water: opposite dangers, opposite jars.

Why Metals Get the Attention

Look around a room and the metals announce themselves. They are lustrous, they conduct heat and electricity, and they are strong. Those properties are exactly the ones you notice, so metals end up seeming like the important half of this chapter. That impression is worth correcting.

The Correction

This should not give the impression that non-metals are unimportant in our lives. The case for them is easy to make, and it starts with something you have done several thousand times since you woke up this morning.

You Are Breathing One

Oxygen is a non-metal, and we draw it in with every breath. Stop it and nobody lasts long. No metal in the room can make that claim. A gas you cannot see, cannot taste and never think about is the single most immediately necessary element in your day.

Carbon Builds You

Carbon matters every day of your life, because every living thing is built from it. Proteins, fats and carbohydrates all have it at their centre, and those three are what growth and energy depend on. So the food on your plate and the body that eats it are both built around a non-metal.

Nitrogen Feeds the Fields

Nitrogen is used in the manufacture of fertilisers and other chemicals. A plant cannot grow well without it either. That is a double role: it goes into the factory that makes the fertiliser, and it is the thing the plant actually needs.

Chlorine Cleans the Water

Chlorine is the non-metal that goes into making water fit to drink. If your tap water is safe to drink, chlorine is a large part of the reason. That is a very ordinary piece of chemistry doing something that used to kill people in large numbers.

Iodine Treats the Wound

Iodine is another non-metal, and its solution is the brown liquid painted onto a cut. You have probably had it painted on a cut knee. Five non-metals, then, and between them they let you breathe, grow, eat, drink safely and heal.

Counting the Score

Set that list against the metal list and the comparison looks different. Metals give you tools, wires, vessels and buildings. Non-metals give you air, food, clean water and medicine. Neither list is dispensable, and that is the honest answer to which group matters more.

Mixing the Two Groups

There is also a way to get the best of both. Many metals and their alloys are important for daily use. An alloy is a mixture of two or more metals, or of a metal and a non-metal. You have already met one: steel mixes iron with carbon.

Where Alloys Go

Alloys are used for utensils and tools, which you meet every day. They matter for modern technology too, and hardly an industry exists without them. So mixing elements is not a laboratory curiosity. It is how most useful metal actually arrives.

Metals for Special Jobs

Some metals are chosen for very particular work. Zirconium is used in atomic energy. Titanium is used in aerospace. These are not metals you will handle, but they show that the choice of a metal is made for a reason rather than out of habit.

Using Metal Twice

Metal that has been used once need not be thrown away. Across India iron and aluminium in particular go back for reuse. The metal is collected, melted and made into something new instead of being dumped.

Why That Matters

Reuse cuts waste and helps resources last. Think about what it saves. A tonne of recycled iron is a tonne that does not have to be dug out of the ground, carried, and processed from scratch. The saving is in the mining as much as in the bin.

Back to Chapter One

This is where the chapter meets the responsibility that chapter one talked about. Understanding that metals can be recycled is knowledge. Separating your metal waste so it can be is the duty that comes with the knowledge.

Counting Both Lists Honestly

It is tempting to settle this by counting objects, and that gives the wrong answer. A room holds far more metal objects than non-metal ones, so metals win on count every time. Ask instead which list you could give up. Nobody can give up breathing, eating or safe water, so length and importance are different questions.

What You Can Now Say

You can sort a material by lustre, hardness, malleability, ductility, sonority and conduction. You can explain rusting and name four ways to stop it. You can predict whether an oxide will be acidic or basic. And you can say why the dull, soft, non-conducting half of the chapter is the half you cannot live without.

Scenario:

Ayesha visits a small town hospital with her aunt. In the dressing room a nurse paints a brown solution onto a cut on a child knee. Outside, a municipal worker adds a measured amount of a chemical to the water tank. That tank feeds the street taps. On the way home they pass a scrap dealer. He is weighing out old iron window frames and crushed aluminium vessels, which go to a furnace to be melted down. Ayesha cousin remarks that the only real science in the town is in the metal yard. The hospital and the water tank, he says, are just routine work.

Analysis:

The cousin has it backwards. Each of the three scenes shows exactly what this chapter describes. The brown solution on the knee is iodine, a non-metal applied to wounds as an antiseptic. The chemical going into the tank is chlorine, what goes into making water fit to drink. That is why the street taps are safe. So two of the three scenes are non-metal chemistry keeping people well. That answers anyone who thinks non-metals are unimportant. The scrap yard is the metal half, and it matters for a different reason. Across India iron and aluminium in particular go back for reuse, which cuts waste. That furnace saves a tonnage nobody has to mine afresh.

Activity:

Over one day, write down five things you use and name the element or alloy behind each. Try to include at least two non-metals. For each one, write a few words saying what job it is doing.

Title:

Audit a day for metals and non-metals

Safety:

No safety precautions are needed for this activity.

What You Notice:

The metal list is usually longer. The non-metal list is harder to give up. Breathing, eating, drinking safe water and treating a cut all appear on the second list. That is why length is a poor measure of importance.

Zirconium is a special metal used in atomic energy, and titanium is used in aerospace.

In India iron and aluminium are recycled in large quantities to minimise waste.

A solution of iodine is painted on a wound because iodine acts as an antiseptic.

OCNCI keeps you going: Oxygen to breathe, Carbon to build, Nitrogen to grow, Chlorine to clean, Iodine to heal.

An alloy can be metal plus metal, or metal plus non-metal: steel is the second kind.