Metals
IGCSE Chemistry Topic 9 13:43 English narration · English + 中文 subtitles burned in
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Why do we dig gold out of the ground as shiny nuggets, but iron only as dull, rusty rock?
为什么我们从地下挖出的金是闪亮的金块，而铁却只是暗淡、生锈的矿石？
And why does a soda can never rust, while an iron nail does?
为什么汽水罐从不生锈，而铁钉却会？
The answer is reactivity — how eagerly a metal reacts.
答案是活泼性——金属反应的急切程度。
Line the metals up from most reactive to least, and you can predict how they react, how they corrode, and even how we get them out of the ground.
把金属从最活泼到最不活泼排成一列，你就能预测它们如何反应、如何腐蚀， 甚至如何把它们从地下提取出来。
Welcome to the chemistry of metals.
欢迎来到金属的化学。
Welcome to metals.
欢迎来到金属。
Their properties, alloys, the reactivity series, rusting, and extraction.
它们的性质、合金、活动性顺序、生锈，还有提取。
Let's begin.
让我们开始吧。
Metals share a set of properties.
金属有一组共同的性质。
Physically, they conduct heat and electricity well — high thermal conductivity, and high electrical conductivity.
物理上，它们导热、导电都很好——导热性高，导电性也高。
They are malleable and ductile — malleability lets you hammer them into sheets, ductility lets you pull them into wires, and neither snaps them.
它们有展性和延性—— 展性让你把它们锤成薄片，延性让你把它们拉成细丝，都不会断裂。
And they usually have high melting points.
而且它们通常熔点很高。
Chemically, metals react in three ways: with an acid to give a salt and hydrogen; with water or steam; and with oxygen to form a metal oxide.
化学上， 金属以三种方式反应：与酸反应生成盐和氢气；与水或蒸汽反应；与氧反应生成金属氧化物。
These properties decide their uses: light aluminium for aircraft, and conducting copper for wiring.
这些性质决定了它们的用途：轻的铝用于飞机，导电的铜用于电线。
Compare metals with non-metals.
把金属与非金属对比。
Metals are good conductors of heat and of electricity.
金属导热、导电都很好。
Non-metals are poor conductors — except graphite, which does conduct electricity.
非金属是不良导体——石墨除外，它能导电。
Metals are malleable and ductile; non-metals are brittle, so they snap when you bend them.
金属有展性和延性；非金属易碎，一弯就会断。
Melting and boiling points are usually high for metals and low for non-metals.
熔点与沸点对金属通常高，对非金属通常低。
This shiny copper is a classic metal: dense, malleable, and an excellent conductor of both heat and electricity.
这块闪亮的铜是典型金属：密度大、可展延，并且导热导电都很出色。
A metal is chosen for a job because of its physical properties.
选某种金属做某项工作，是因为它的物理性质。
Aluminium makes aircraft bodies because it has low density — it is light, so the plane stays light.
铝用来造飞机机身，因为它密度低——轻， 所以飞机也轻。
Aluminium is also used for overhead electrical cables: low density plus good conductivity.
铝还用于架空电缆：密度低，又导电好。
Food containers use aluminium because it resists corrosion.
食品容器用铝，因为它耐腐蚀。
Copper is chosen for electrical wiring because it conducts electricity well and is ductile, so it can be drawn into thin wires without breaking.
铜被选来做电线，因为导电好，又有延性，可以拉成细丝而不断。
Most metals we use are not pure — they are alloys.
我们使用的大多数金属并不纯——它们是合金。
An alloy is a mixture of a metal with one or more other elements.
合金是金属与一种或多种其他元素的混合物。
Brass is copper mixed with zinc; stainless steel is iron mixed with chromium and others.
黄铜是铜和锌的混合；不锈钢是铁和铬等的混合。
Why bother?
为什么要这样？
Because alloys are harder and stronger.
因为合金更硬、更强。
Here's why.
原因是这样。
In a pure metal, the atoms are all the same size, so the layers can slide over each other easily — that makes it soft.
在纯金属中，原子大小都一样，所以层能轻易地彼此滑动——这让它变软。
In an alloy, the different-sized atoms jam the layers, stopping them from sliding.
在合金中，不同大小的原子卡住了层，阻止它们滑动。
So the alloy is harder.
所以合金更硬。
Look at the two grids.
看这两张网格。
On the left, every atom is the same size, so the rows can slide past each other — that is why pure metals are soft.
左边每个原子大小相同，所以各行能彼此滑过——这就是纯金属偏软的原因。
On the right, some atoms are larger.
右边有些原子更大。
They distort the rows and block sliding, so the alloy is harder and stronger.
它们扭曲了各行并挡住滑动，所以合金更硬更强。
Brass is copper plus zinc.
黄铜是铜加锌。
Stainless steel is iron mixed with chromium, nickel and carbon — it is used for cutlery because it is hard and does not rust.
不锈钢是铁与铬、镍和碳的混合——用来做餐具，因为硬，而且不生锈。
Different-sized atoms are the whole secret of alloy strength.
不同大小的原子就是合金强度的全部秘密。
Here is the most useful list in metal chemistry: the reactivity series.
这是金属化学中最有用的一张表：金属活动性顺序。
From most reactive at the top to least at the bottom: potassium, sodium, calcium, magnesium, aluminium, then carbon, then zinc, iron, hydrogen, copper, silver, and gold.
从顶部最活泼到底部最不活泼： 钾、钠、钙、镁、铝，然后是碳，然后是锌、铁、氢、铜、银、金。
The higher a metal, the more easily it forms positive ions, and the more eagerly it reacts.
金属越靠上， 就越容易形成正离子，反应就越急切。
Potassium and sodium react with cold water.
钾和钠与冷水反应。
Magnesium, zinc, and iron react with acid.
镁、锌、铁与酸反应。
But copper, silver, and gold barely react at all — which is why gold is found shining in the ground.
但铜、银、金几乎不反应——这就是为什么金在地下闪闪发光。
Carbon and hydrogen sit in the list for comparison, even though they are not metals.
碳和氢也在表里作比较，尽管它们不是金属。
Read the reactions carefully.
仔细看反应。
Potassium, sodium and calcium react with cold water.
钾、钠和钙与冷水反应。
Magnesium reacts with steam, but only very slowly with cold water.
镁与蒸汽反应，但与冷水反应非常慢。
Magnesium, zinc and iron react with dilute hydrochloric acid; copper, silver and gold do not.
镁、锌和铁与稀盐酸反应；铜、银和金不反应。
The diagram also shows extraction: metals above carbon need electrolysis; metals below carbon can be heated with carbon.
图中还显示提取方法：碳以上的金属需要电解；碳以下的金属可以与碳一起加热。
Learn the order cold — exams quote it again and again.
把顺序背牢——考试会反复考到。
Aluminium sits high in the series, so you might expect it to react fiercely.
铝在活动性顺序中位置很高，所以你可能以为它会剧烈反应。
In practice it seems less reactive than its place suggests.
实际上它看起来不如其位置那么活泼。
Why?
为什么？
A thin, strong oxide layer coats the metal and stops other substances reaching the aluminium underneath.
一层又薄又结实的氧化层覆盖着金属， 阻止其他物质接触下面的铝。
That protective skin is why an aluminium can does not corrode the way bare iron does.
正是这层保护皮，让铝罐不会像裸铁那样腐蚀。
Remember: position in the series is the true reactivity; the oxide layer just hides it.
记住：在顺序中的位置才是真正的活泼性；氧化层只是把它藏起来了。
A more reactive metal will displace a less reactive one from a solution of its ions.
较活泼的金属会把较不活泼的从它的离子溶液中置换出来。
Zinc is more reactive than copper.
锌比铜活泼。
So drop a piece of zinc into blue copper sulfate solution, and watch.
所以把一块锌放进蓝色的硫酸铜溶液里，看着。
The zinc pushes the copper out.
锌把铜挤出来。
The blue colour fades, because the copper ions are being used up.
蓝色褪去， 因为铜离子被用掉了。
A pink-brown solid — the copper — coats the zinc.
一种粉棕色的固体——铜——覆盖在锌上。
And the mixture warms up, because displacement gives out heat.
混合物变热， 因为置换放出热量。
The more reactive metal always wins.
更活泼的金属总是获胜。
Exams award separate marks for what you would see.
考试对你“会看到什么”单独给分。
For zinc in copper sulfate: the blue colour of the solution fades, because blue copper two-plus ions are used up and zinc sulfate is colourless.
锌放进硫酸铜：溶液的蓝色褪去，因为蓝色的二价铜离子 被用掉，而硫酸锌是无色的。
A pink-brown solid coats the zinc — that is the displaced copper.
粉棕色固体覆盖在锌上——那是被置换出的铜。
The grey zinc dissolves and gets smaller.
灰色的锌溶解并变小。
The mixture warms up, because displacement is exothermic.
混合物变热，因为置换是放热的。
Word equation: zinc plus copper sulfate gives zinc sulfate plus copper.
文字方程式：锌加硫酸铜生成硫酸锌加铜。
Observations, not just the formula, earn marks.
观察现象，而不只是化学式，才能得分。
Metal-and-acid reactions have their own observation list.
金属与酸的反应有自己的观察清单。
You see effervescence — that is the hydrogen gas escaping as bubbles — and the solid metal dissolves.
你会看到泡腾——那是氢气以气泡逃出——以及固体金属溶解。
Never write “hydrogen is given off” as an observation.
永远不要把“放出氢气”写成观察现象。
You cannot see the gas itself, only the bubbles, so write effervescence.
你看不见气体本身，只能看见气泡，所以要写泡腾。
With copper oxide or copper carbonate plus acid, add that the solution turns blue as copper two-plus ions form.
用氧化铜或碳酸铜加酸时，还要写溶液变蓝，因为生成了二价铜离子。
Name the bubbles and the colour change, and you bank the marks.
点出气泡和颜色变化，就能稳拿这些分。
Corrosion slowly eats away unprotected metal.
腐蚀会慢慢侵蚀没有保护的金属。
This post has been attacked by air and moisture over years.
这根柱子多年来被空气和湿气侵蚀。
Not every metal corrodes the same way.
不是每种金属都以同样方式腐蚀。
Gold barely corrodes at all.
金几乎不腐蚀。
Iron is different: its special form of corrosion has a name you must know — rusting.
铁不同：它这种特殊的腐蚀有一个 你必须知道的名字——生锈。
Understanding what rusting needs is the key to stopping it.
弄清生锈需要什么，是阻止它的关键。
Now, corrosion.
现在说腐蚀。
Rusting is the corrosion of iron, and it needs two things: oxygen from the air, and water.
生锈是铁的腐蚀，它需要两样东西：空气中的氧和水。
Take away either one, and the iron will not rust.
去掉任何一样， 铁就不会生锈。
So how do we stop it?
那我们怎样阻止它？
Barrier methods keep the air and water out: painting, greasing — covering the metal with oil — or coating it with plastic.
隔离法把空气和水挡在外面：涂漆、涂油脂（在金属表面覆盖一层油）或包塑料。
But there's a cleverer way — galvanising, coating iron with zinc.
但还有一种更巧妙的方法——镀锌，给铁镀上一层锌。
The zinc is a barrier, but it also gives sacrificial protection.
锌是屏障，但它还提供牺牲保护。
Because zinc is more reactive than iron, the zinc corrodes first, giving up its electrons to protect the iron — even if the surface is scratched.
因为锌比铁活泼，锌会先腐蚀，交出它的电子来保护铁——即使表面被划破。
Here is rusted iron in the real world — a heavy chain on coastal rocks.
这是现实中生锈的铁——沿海礁石上的一条重链。
Sea water and air have turned the metal orange-brown.
海水和空气把金属变成了橙棕色。
The rust formed is hydrated iron three oxide.
形成的铁锈是水合三氧化二铁。
Only iron and steel rust in this sense; other metals corrode, but we reserve the word rusting for iron.
只有铁和钢会以这种意义生锈；其他金属会腐蚀， 但“生锈”这个词我们留给铁。
Wet salty air is especially aggressive, which is why coastal iron needs strong protection.
潮湿的含盐空气特别具有侵蚀性， 所以海边的铁需要更强的保护。
Three test tubes prove the rule.
三支试管证明这条规则。
In the first, an iron nail sits in water with air above it — both water and oxygen are present, so the nail rusts.
第一支里，铁钉在水中，上方有空气——水和氧都有，所以钉生锈。
In the second, boiled water under a layer of oil has almost no dissolved oxygen, and the seal keeps air out — no rust.
第二支里，沸水上方有一层油，几乎没有溶解的氧，密封也挡住了空气——不生锈。
In the third, dry air with a drying agent has oxygen but no water — again no rust.
第三支里，带干燥剂的干燥空气有氧但没有水——也不生锈。
Only the tube that has both water and oxygen shows rust.
只有同时有水和氧的试管才出现锈。
That is the experiment examiners love.
这就是考官喜爱的实验。
Galvanising coats iron with zinc.
镀锌是给铁镀一层锌。
It works two ways.
它有两种作用。
First it is a barrier: the zinc keeps out air and water.
第一是屏障：锌挡住空气和水。
Second it gives sacrificial protection.
第二是牺牲保护。
Zinc is more reactive than iron, so the zinc loses electrons and corrodes instead of the iron.
锌比铁活泼，所以锌失去电子并代替铁腐蚀。
Even if the coating is scratched and bare iron shows, the zinc still protects it by sacrificing itself.
即使镀层被划破、露出裸铁， 锌仍然会牺牲自己来保护铁。
Painting only works while the paint is whole; galvanising keeps working after damage.
油漆只有完整时才有效；镀锌在破损后仍然有效。
How do we get a metal out of its ore?
我们怎样把金属从矿石里提取出来？
The reactivity series decides the method, and the key line is carbon.
金属活动性顺序决定方法，而关键的界线是碳。
Metals below carbon — like iron, copper, and zinc — are less reactive than carbon, so carbon can pull the oxygen away from them.
碳以下的金属——比如铁、铜、锌——比碳不活泼，所以碳能把氧从它们那里夺走。
They are extracted by heating with carbon.
它们通过与碳一起加热来提取。
But metals above carbon — like aluminium, sodium, and potassium — are too reactive; carbon cannot budge them.
但碳以上的金属——比如铝、钠、钾——太活泼了； 碳撼动不了它们。
They must be extracted by electrolysis, which is far more expensive.
它们必须通过电解来提取，那要贵得多。
That is why aluminium costs more to produce than iron.
这就是为什么生产铝比铁更贵。
This map puts the rule on one picture.
这张图把规则画在一张图上。
Above carbon: potassium, sodium, calcium, magnesium, aluminium — too reactive for carbon, so use electrolysis.
碳以上：钾、钠、钙、镁、铝——对碳来说太活泼，所以用电解。
Below carbon: zinc, iron, copper — less reactive than carbon, so heat the ore with carbon to strip away the oxygen.
碳以下：锌、铁、铜——比碳不活泼，所以把矿石与碳一起加热，夺走氧。
An ore is a rock that holds enough metal compound to be worth extracting.
矿石是含有足够金属化合物、值得提取的岩石。
Place the metal relative to carbon first, then choose the method.
先把金属相对碳放好位置，再选方法。
Worked example.
例题。
Zinc and aluminium are both found as oxides.
锌和铝都以氧化物形式存在。
Which can be extracted by heating with carbon, and why?
哪一种可以用与碳加热来提取，为什么？
Find each metal relative to carbon in the series.
在活动性顺序中找到每种金属相对碳的位置。
Zinc sits below carbon, so carbon is more reactive and can take the oxygen away: zinc oxide is reduced by heating with carbon.
锌在碳以下，所以碳更活泼，能夺走氧： 氧化锌通过与碳加热被还原。
Aluminium sits above carbon, so carbon is not reactive enough to displace it.
铝在碳以上，所以碳不够活泼，无法置换它。
Aluminium must be extracted by electrolysis instead — which is why aluminium costs far more.
铝必须用电解提取——这就是铝贵得多的原因。
The deciding line is carbon's place, not the top of the list.
决定线是碳的位置，不是表的顶端。
Two examples you must know.
有两个例子你必须知道。
Iron is extracted in a blast furnace.
铁在高炉中提取。
Carbon burns to make carbon monoxide, and the carbon monoxide reduces the iron ore to iron.
碳燃烧生成一氧化碳，一氧化碳把铁矿还原成铁。
Limestone removes the sandy impurities as slag.
石灰石把沙质杂质以炉渣的形式除去。
Aluminium is extracted by electrolysis.
铝通过电解提取。
Its ore is dissolved in molten cryolite to lower the melting point.
它的矿石溶解在熔融的冰晶石里以降低熔点。
At the negative cathode, aluminium forms; at the positive anode, oxygen forms, which slowly burns away the carbon anodes.
在负极阴极，生成铝；在正极阳极，生成氧，氧慢慢烧掉碳阳极。
Iron comes from the ore hematite — iron three oxide — in a blast furnace.
铁来自矿石赤铁矿——三氧化二铁——在高炉中提取。
Step by step.
一步一步看。
Carbon, as coke, burns in hot air to give carbon dioxide and lots of heat.
碳，也就是焦炭， 在热空气中燃烧生成二氧化碳并放出大量热。
That carbon dioxide reacts with more carbon to form carbon monoxide.
二氧化碳再与更多碳反应生成一氧化碳。
The carbon monoxide reduces the iron three oxide to iron — reduction means oxygen is removed.
一氧化碳把三氧化二铁还原成铁——还原就是去掉氧。
Limestone, which is calcium carbonate, breaks down in the heat to calcium oxide.
石灰石是碳酸钙，受热分解成氧化钙。
Calcium oxide reacts with sandy impurities to form slag, which is tapped off.
氧化钙与沙质杂质反应生成炉渣，被放出。
Molten iron collects at the bottom.
熔融的铁积在底部。
Aluminium is extracted from bauxite.
铝从铝土矿提取。
The ore is purified to aluminium oxide, then dissolved in molten cryolite.
矿石先提纯成氧化铝，再溶解在熔融的冰晶石中。
Cryolite lowers the melting point, which saves a huge amount of energy.
冰晶石降低熔点，从而节省大量能量。
At the cathode — the negative electrode — aluminium ions gain electrons and form aluminium metal.
在阴极——负电极——铝离子得到电子，生成铝金属。
At the anode — the positive electrode — oxygen forms.
在阳极——正电极——生成氧。
That oxygen reacts with the hot carbon anodes and burns them away, so the anodes must be replaced regularly.
氧与炽热的碳阳极反应并把它们烧掉，所以阳极必须定期更换。
Costly electricity plus replaceable anodes explain the high price of aluminium.
昂贵的电力加上可更换的阳极，解释了铝的高价格。
Three marks to lock in.
锁住三个分。
First: learn the reactivity series, potassium to gold; a more reactive metal displaces a less reactive one from its solution.
第一：记住金属活动性顺序，钾到金；较活泼的金属把较不活泼的从它的溶液中置换出来。
Second: metals above carbon are extracted by electrolysis, those below carbon by heating with carbon.
第二：碳以上的金属通过电解提取，碳以下的通过与碳加热提取。
Third: rusting needs both water and oxygen; galvanising protects iron because the more reactive zinc corrodes instead.
第三：生锈需要水和氧两者； 镀锌保护铁，因为较活泼的锌会代替铁腐蚀。
Master these, and this topic is yours.
掌握这些，这个专题就是你的了。
One more mark-winner.
再锁一个得分点。
Alloys are harder than pure metals because the different-sized atoms stop the layers of ions sliding over each other.
合金比纯金属更硬，因为不同大小的原子阻止离子层彼此滑动。
If an exam asks why steel is harder than pure iron, or why brass is used instead of pure copper, that is the answer — mixed atom sizes jam the layers.
如果考试问为什么钢比纯铁硬，或为什么用黄铜而不用纯铜，答案就是这个—— 混合的原子大小卡住了各层。
Link the structure picture to the property every time, and you will not lose easy marks on alloys.
每次都把结构图与性质联系起来，就不会在合金上丢简单分。