Various kinds of object are found around us, and they are used for various works. A selection is made for a definite job on the basis of the property and the characteristic that an object has. Because heat is conducted through them, cooking pots are made from aluminium and steel. Because electricity flows well through it, copper is used to make electric wire. And because electricity does not pass through it, plastic is used as an insulator on the outside of that wire. In this way, making various properties the basis, the elements have been classified into two groups: metal and non-metal.
Elements that are hard, that have a lustre, that get hot when they are heated, that get flattened when they are hammered and that make a ringing sound are metals, for example iron, copper, gold, silver and aluminium. In the same way, elements that are soft, that do not shine, that burn when they are heated and that do not conduct heat and electricity are non-metals, for example sulphur, iodine and carbon.
You are about to meet the word ore six times in six pages, and the book never stops to define it, yet the exercise asks you for the difference between a mineral and an ore. So here it is. A mineral is any solid substance that occurs naturally in the ground with a definite composition; there are thousands of them and most are of no use to anybody. An ore is a mineral from which a metal can actually be taken out in a useful amount and at a sensible cost. So every ore is a mineral, but only a few minerals are worth calling ores, and the same shape of sentence turns up again from the last topic, where every alkali was a base but not every base was an alkali. Bauxite is a mineral, and because aluminium can be got out of it in quantity, it is also the ore of aluminium. The metal itself is what comes out at the end, after refining, and it looks nothing like the rock it started in, which is worth remembering when you look at the photographs on the next few pages.
Aluminium
Symbol: Al. Atomic number: 13. Aluminium is not found in a pure form in nature, but is found in plenty as an impure substance, an ore, mixed with compounds or with other substances. Its main ore is bauxite, and aluminium is refined from it.
| Physical property | What it is used for |
|---|---|
| Aluminium is a white, light metal | Making the outer structure of vehicles and aeroplanes |
| It is a good conductor of electricity | Making electric wire |
| It is a good conductor of heat | Making household cooking utensils |
| It can be melted at a low temperature | Making aluminium sheets and wires |
| Air and water do not affect it | Making aluminium foil for packing food |
The book says air and water do not affect aluminium, which is exactly what you observe, but the reason is not that aluminium ignores the air. Aluminium is in fact a reactive metal and it starts reacting with oxygen the moment a fresh surface is exposed. What saves it is the layer it forms. Aluminium oxide is thin, hard and stays firmly stuck to the metal underneath, so it seals the surface and nothing further can get in. Compare that with iron. Iron also reacts with air and water, but rust is flaky and weak and falls away, exposing fresh iron beneath, so the rusting simply carries on until the whole piece is eaten through. That is the entire difference between a metal that protects itself and one that must be painted, and it is why the iron gate at your school needs repainting while the aluminium window frame beside it has never been touched. This is the same idea you met in Unit 9 when you asked why gates are painted, seen now from the metal side.
Zinc
Symbol: Zn. Atomic number: 30. Zinc is found in nature as ore and as compound. Its main ore is zinc blende, and zinc is refined from it.
| Physical properties | Uses |
|---|---|
| This metal is of a light blue crystal shape | Used in the laboratory to prepare hydrogen gas |
| It is a conductor of heat and electricity | Used to make alloys such as brass and bronze |
| Cold and water affect it | Used to make the outer covering of a dry cell |
| It can be melted at a comparatively low temperature | Used to make printing blocks, and zinc sheets for roofing |
The corrugated sheets on half the roofs in Nepal are called jasta pata, which sounds as though they were made of zinc. They are not. They are thin iron sheets with a coating of zinc on the outside, and that coating is what galvanising means. Iron on its own would rust through in a few monsoons; the zinc keeps the rain and air off it. And here is the part worth knowing, because it is genuinely surprising: zinc protects iron even where the coating gets scratched. Zinc is the more reactive of the two, so it corrodes in place of the iron rather than letting the iron corrode, which is why a galvanised sheet with a scrape in it does not immediately start rusting at that spot. Notice which exercise question this answers: which metal is generally used in galvanisation. The answer is zinc, and now you know not just that it is, but why it works.
Iron
Symbol: Fe. Atomic number: 26. In nature iron is found in the form of ore. Iron is mainly refined from haematite ore.
| Physical properties | Uses |
|---|---|
| Iron is a black, grey coloured metal | Making various kinds of tools and weapons |
| It shines when it is rubbed | Making household utensils |
| It rusts | Making houses, bridges and means of transport |
| It has magnetic property | Producing steel |
| Air and water affect this metal easily | Producing rods, pipes and wire |
Gold
Symbol: Au. Atomic number: 79. In nature gold is found in a pure state. It is found in the middle of rocks and in the sand of rivers.
| Physical properties | Uses |
|---|---|
| Gold is a shining yellow coloured metal | Making ornaments |
| It is a conductor of heat and electricity | Making statues of gods and goddesses, coins and medals |
| It is an inactive metal | Plating on other metals |
| It does not react with air and water | Making medicine |
| It is the metal with the most ductility, so it can be drawn into the longest and thinnest wire | Plating on teeth |
Copper
Symbol: Cu. Atomic number: 29. Copper is a metal that people have been using since very early times. Copper is found in nature in the form of ore, and it is mainly refined from chalcopyrite ore.
| Physical properties | Uses |
|---|---|
| Copper is a red brown coloured metal | Making utensils |
| It conducts heat and electricity, and is the best conductor after silver | Making electric wires |
| It becomes tarnished in cold | Making alloys such as brass and bronze |
| It can be beaten into a ball or flattened, and drawn into wire | Making copper coins, statues, medals, chemicals and medicine |
Silver
Symbol: Ag. Atomic number: 47. Silver can be obtained in nature in the form of ore and of compound. Its main ore is argentite, and silver is refined from it.
| Physical properties | Uses |
|---|---|
| Silver is a white metal with a lustre | Making precious utensils, coins and medals |
| It is the best conductor of heat and electricity of all | Making ornaments |
| Air and water do not affect it | Plating on other metals |
| It is a less active metal | Filling the empty spaces in teeth, and making medicine |
Six metals on one page
| Metal | Symbol | Atomic no. | Main ore | The property that matters most |
|---|---|---|---|---|
| Aluminium | Al | 13 | Bauxite | Light, and unaffected by air and water |
| Zinc | Zn | 30 | Zinc blende | Protects iron underneath it, which is galvanising |
| Iron | Fe | 26 | Haematite | Strong and magnetic, but it rusts |
| Gold | Au | 79 | None. Found already pure | Inactive, and the most ductile of all metals |
| Copper | Cu | 29 | Chalcopyrite | Second best conductor, and affordable |
| Silver | Ag | 47 | Argentite | The best conductor of all, and expensive |
Aluminium is Al and zinc is Zn, which anybody could guess. But iron is Fe, gold is Au, copper is Cu and silver is Ag, and none of those come from the English word at all. They come from Latin: ferrum, aurum, cuprum and argentum. That is not a piece of trivia, it is a clue about history. These four metals were known and named long before English existed, because they are the metals a person can find and work without modern chemistry, and the Latin names simply stayed. You met the same thing in Unit 9 with sodium as Na from natrium and potassium as K from kalium. Notice too that argentite, the ore of silver, carries argentum inside it, so the ore is named after the metal, not the other way round.
Read the six entries again and a pattern appears that the book never points at. Metals can be put in order of how eagerly they react with other things, and where a metal sits on that ladder decides three separate facts about it at once. Gold is right at the bottom, barely reacting with anything, so it is found already pure in rocks and river sand, it never tarnishes, and it needed no chemistry at all to discover, which is why gold ornaments are thousands of years old. Silver is just above it: nearly inactive, mostly found as an ore but sometimes pure, and it tarnishes slowly. Copper is higher still, always an ore, and it goes dull and then green with age. Iron is higher again, always an ore, and it rusts away completely if left alone. Aluminium and zinc are higher than all of them, never found pure, and both react so readily that they form a protective coat almost instantly. So the answer to why is gold found pure, why does iron rust, and why were gold and copper used thousands of years before aluminium is one answer, not three: it is the ladder.
The book states both facts on separate pages and never puts them side by side. Silver is the best conductor of heat and electricity there is; copper is the best after silver. So why is the wiring in every house in the country made of copper? Money. Silver is many times more expensive, and the improvement it buys is small, so no sensible person would pay a fortune to make a wire a little better when a cheap one already works. Aluminium is cheaper again and a little worse than copper, which is why the enormous cables carried on transmission towers across the country are aluminium and not copper: over hundreds of kilometres, weight and cost matter more than the last bit of conductivity. And silver does get used, in tiny quantities, at the contact points inside good switches and instruments, where the amount needed is small and the performance is worth it. This is engineering rather than pure chemistry: the best material and the right material are often not the same thing.
Two of the metals above keep appearing as ingredients rather than as finished objects, so it is worth naming what they are ingredients of. An alloy is a metal mixed with one or more other metals to get properties that neither one had alone. Brass is copper mixed with zinc: harder than copper, easy to shape, and it does not corrode quickly, which is why taps, locks and temple ornaments are made of it. Bronze is copper mixed with tin: harder still, and the metal that bells and old statues are cast from, because it rings well and lasts for centuries. Steel, which the iron section mentions, is the same idea from the other direction: iron mixed with a small amount of carbon, which makes it far stronger than iron alone. Notice that every alloy in that list is a mixture, not a compound, which takes you straight back to Unit 9.
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