The Periodic Table
IGCSE Chemistry Topic 8 11:15 English narration · English + 中文 subtitles burned in
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This is the most powerful chart in all of chemistry: the Periodic Table.
这是全化学中最强大的图表：周期表。
It looks like a jumble of boxes, but it hides a beautiful secret.
它看起来像一堆杂乱的方格，却隐藏着一个美妙的秘密。
The elements are arranged so that, just by knowing where an element sits, you can predict how it behaves.
元素的排列方式使得，只要知道一个元素在哪里，你就能预测它的行为。
Soft metals that explode in water sit in one column.
遇水会爆炸的柔软金属排在一列。
Colourful, poisonous gases sit in another.
多彩、有毒的气体排在另一列。
Today we learn to read the table like a map.
今天我们要学会像读地图一样读这张表。
Welcome to the Periodic Table.
欢迎来到周期表。
Groups and periods, the alkali metals, the halogens, and the noble gases.
族与周期、碱金属、卤素，还有稀有气体。
Let's begin.
让我们开始吧。
The Periodic Table arranges all the elements in order of increasing proton number.
周期表按质子数递增的顺序排列所有元素。
The rows are called periods; the columns are called groups.
行叫做周期；列叫做族。
Across a period, elements change from metals on the left to non-metals on the right.
沿着一个周期， 元素从左边的金属变到右边的非金属。
The real magic is the groups.
真正神奇的是族。
Elements in the same group have the same number of outer-shell electrons, so they react in very similar ways.
同一族的元素有相同数目的外层电子， 所以它们的反应方式非常相似。
The group number even tells you the charge of the ion: Group one forms plus-one ions, Group seven forms minus-one ions.
族数甚至告诉你离子的电荷：第一族形成正一价离子， 第七族形成负一价离子。
Here is a real Periodic Table, with samples of many elements.
这是一张真实的周期表，许多元素都有样品。
The order is not random.
顺序并非随机。
Every element has a proton number — also called the atomic number — and the table climbs one proton at a time from left to right, then down to the next row.
每个元素都有质子数——也叫原子序数——表从左到右每次增加一个质子， 然后进入下一行。
Hydrogen is number one; helium is number two.
氢是一号；氦是二号。
That simple rule is the backbone of the whole chart.
这条简单的规则是整张表的骨架。
Once you know an element's place, you already know a lot about how it will behave.
一旦知道元素的位置，你就已经知道它许多行为。
This schematic makes the map clear.
这张示意图把地图说清楚了。
Groups are the numbered columns; periods are the rows.
族是编号的列；周期是行。
Metals sit on the left in blue; non-metals sit on the right in cream.
金属在左边蓝色区域；非金属在右边米色区域。
A staircase line divides them.
一条阶梯线把它们分开。
Group two sits next to Group one, and those metals form plus-two ions.
第二族紧挨第一族，那些金属形成正二价离子。
Transition metals fill the middle block.
过渡金属填满中间的区块。
Use position to predict: left means metal-like; right means non-metal-like; same group means the same outer-shell electron count and similar chemistry.
用位置来预测：左边偏金属性；右边偏非金属性；同一族外层电子数相同，化学性质相似。
Group one are the alkali metals: lithium, sodium, and potassium.
第一族是碱金属：锂、钠和钾。
They are so soft you can cut them with a knife.
它们非常柔软，你可以用刀切开。
They all react with water to make an alkali — the metal hydroxide — plus hydrogen gas.
它们都与水反应生成碱—— 金属氢氧化物——加氢气。
Drop sodium on water, and it floats, melts into a ball, and darts around, fizzing.
把钠放到水上，它会浮起、熔成小球、四处窜动、冒泡。
The solution turns alkaline.
溶液变成碱性。
Going down the group, they get more reactive: lithium fizzes gently, sodium darts about, and potassium bursts into a lilac flame.
沿着这一族往下，它们越来越活泼：锂轻轻冒泡，钠四处窜动， 钾则爆出淡紫色的火焰。
Why do lithium, sodium and potassium behave so alike?
为什么锂、钠和钾的行为如此相似？
Look at their electron shells.
看它们的电子层。
Every Group one atom has exactly one electron in its outer shell.
每一个第一族原子的外层都恰好只有一个电子。
That single outer electron is easy to lose, so each metal forms a plus-one ion.
那个单独的外层电子很容易失去， 所以每种金属都形成正一价离子。
Same outer electronic configuration means same chemistry — that is the group rule in action.
相同的外层电子排布意味着相同的化学——这就是族规则在起作用。
The further down you go, the outer electron sits further from the nucleus, so it is lost even more easily.
越往下，外层电子离原子核越远，也就越容易失去。
That is why reactivity rises down the group.
这就是为什么活泼性沿族向下增强。
Three clear trends run down Group one.
沿第一族往下有三条清晰趋势。
Melting point decreases — the metals get easier to melt as you go down.
熔点降低——越往下金属越容易熔化。
Density increases — the atoms pack more mass into each bit of volume.
密度增大——原子把更多质量装进同样体积。
Reactivity increases — lithium is the calmest of the three; potassium is the fiercest.
活泼性增强——锂是三者中最温和的； 钾最猛烈。
You can predict elements you have not met.
你还能预测没见过的元素。
Rubidium sits below potassium, so it should be even more reactive, and it should have an even lower melting point.
铷在钾的下方，所以它应该更活泼， 熔点也应该更低。
Trends turn the table into a prediction machine.
趋势把周期表变成了预测机器。
Watch potassium on water.
看钾与水的反应。
The reaction is so fast that the hydrogen gas catches fire, burning with a lilac flame and a burst of sparks.
反应快到氢气着火，以淡紫色火焰燃烧，并溅出火花。
That lilac colour is a classic potassium fingerprint in the exam.
那种淡紫色是考试里钾的经典指纹。
Lithium only fizzes steadily and does not melt.
锂只是稳定冒泡，并不熔化。
Sodium melts into a ball and darts about.
钠熔成小球四处窜动。
Potassium is violent enough to ignite its own hydrogen.
钾猛烈到点燃自己放出的氢气。
The same reaction, three levels of drama — that is the reactivity trend made visible.
同一类反应，三种激烈程度——这就是看得见的活泼性趋势。
The exam loves one question: describe what you see when sodium meets water.
考试很爱一道题：描述钠遇水时你看到什么。
Learn the list.
把清单记牢。
The metal floats — it is less dense than water.
金属浮起——它比水密度小。
It melts into a ball — the reaction gives out heat, and sodium's melting point is low.
它熔成小球——反应放热，且钠熔点低。
It moves about — a jet of hydrogen pushes it.
它四处移动——一股氢气推动它。
There is effervescence, meaning fizzing from the gas.
有泡腾，也就是气体冒泡。
The piece gets smaller and disappears.
金属块变小并消失。
The solution turns alkaline, so universal indicator goes purple.
溶液变碱性，所以通用指示剂变紫。
The equation is two sodium plus two water makes two sodium hydroxide plus hydrogen.
方程式是两个钠加两份水生成两份氢氧化钠加氢气。
Two traps: do not say "hydrogen is given off" — you cannot see the gas; say effervescence.
两个陷阱：不要说放出氢气—— 你看不见那种气体；要说泡腾。
And the metal melts because the reaction is exothermic, not because the water was hot.
金属熔化是因为反应放热，不是因为水本来就热。
Group seven are the halogens: chlorine, bromine, and iodine.
第七族是卤素：氯、溴和碘。
They are non-metals, and each exists as a molecule of two atoms — that's what diatomic means.
它们是非金属，每一个都以两个原子组成的分子存在—— 这就是双原子的意思。
Look at how they change down the group.
看它们沿着这一族怎样变化。
Chlorine is a pale yellow-green gas.
氯是淡黄绿色的气体。
Bromine is a red-brown liquid.
溴是红棕色的液体。
Iodine is a grey-black solid.
碘是灰黑色的固体。
They get darker and denser going down.
往下走，它们越来越深、越来越密。
But unlike the alkali metals, the halogens get less reactive as you go down the group.
但和碱金属不同， 卤素往下走会越来越不活泼。
Put the two groups side by side on one diagram.
把两个族放在同一张图上并排比较。
Down Group one, the arrow of reactivity points down: lithium, then sodium, then potassium get fiercer.
沿第一族往下，活泼性箭头向下：锂、钠、钾越来越猛。
Down Group seven the arrow is the other way: chlorine is the most reactive halogen of the three, then bromine, then iodine.
沿第七族箭头相反：氯是三者中最活泼的卤素，然后是溴，再是碘。
Density still rises down both groups, but reactivity runs in opposite directions.
密度在两个族里都往下增大，但活泼性方向相反。
Memorise that pair of arrows — it unlocks every displacement prediction.
记住那一对箭头——它解锁每一次置换预测。
This difference in reactivity leads to displacement reactions.
这种活泼性的差异导致了置换反应。
A more reactive element pushes a less reactive one out of its salt solution.
较活泼的元素会把较不活泼的从它的盐溶液中挤出去。
Watch a strip of zinc in blue copper sulfate.
看一片锌放进蓝色的硫酸铜溶液。
Zinc is more reactive than copper, so the zinc takes the copper's place.
锌比铜活泼，所以锌取代铜的位置。
Copper coats the strip, and the blue colour fades away.
铜镀在锌片上，蓝色渐渐褪去。
The halogens follow the very same rule: the more reactive element always wins, and shoves the weaker one out.
卤素遵循完全相同的规则：更活泼的元素总是获胜，把较弱的挤出去。
The colour change is the observation mark.
颜色变化就是观察分。
Start with colourless potassium bromide solution.
从无色的溴化钾溶液开始。
Add chlorine, which is more reactive.
加入更活泼的氯。
Chlorine displaces the bromide ion, and free bromine appears — the solution turns orange.
氯置换溴离子，游离的溴出现——溶液变成橙色。
In symbols on the page: chlorine plus two potassium bromide gives two potassium chloride plus bromine.
纸上的符号是： 氯加两份溴化钾生成两份氯化钾加溴。
The more reactive halogen takes the place of the less reactive halide in the salt.
较活泼的卤素取代盐中较不活泼的卤离子。
Always name the colour you expect, not just "a reaction happens".
永远说出你期望的颜色，而不只是说发生了反应。
Worked example.
例题。
First, aqueous chlorine is added to potassium iodide solution.
第一，把氯水加入碘化钾溶液。
Reactivity falls down Group seven: chlorine, then bromine, then iodine.
活泼性沿第七族向下降低：氯、溴、碘。
Chlorine sits above iodine, so it is more reactive and displaces it.
氯在碘上方，所以更活泼并置换它。
Chlorine plus two potassium iodide makes two potassium chloride plus iodine, and the solution turns red-brown as iodine is released.
氯加两份碘化钾生成两份氯化钾加碘， 溶液因碘释放而变成红棕色。
Second, aqueous iodine is added to potassium bromide.
第二，把碘水加入溴化钾。
Iodine sits below bromine, so it is less reactive and cannot displace it.
碘在溴下方，所以不那么活泼，无法置换。
There is no reaction and no colour change.
没有反应，也没有颜色变化。
"No reaction" is a full answer worth marks — check the order in the group before you write any equation.
没有反应是完整答案，能拿分——写任何方程式之前先检查族里的顺序。
Let's put the trends side by side.
让我们把趋势并排放。
Down Group one, reactivity increases.
沿第一族往下，活泼性增加。
Down Group seven, reactivity decreases — the exact opposite.
沿第七族往下，活泼性减小——正好相反。
Use this to predict displacement.
用这个来预测置换。
Will iodine displace bromine?
碘能置换溴吗？
Iodine sits below bromine in Group seven, so iodine is less reactive.
碘在第七族里位于溴的下方，所以碘不那么活泼。
A less reactive halogen cannot displace a more reactive one — so there is no reaction.
较不活泼的卤素无法置换较活泼的——所以没有反应。
Always check the order in the group before you write an equation.
写方程式之前，永远先检查族里的顺序。
In the middle of the table sits a block of special metals: the transition elements.
在表的中间，坐落着一组特殊的金属：过渡元素。
Compared with the alkali metals, they are hard and dense, with high melting points.
和碱金属相比，它们又硬又密，熔点很高。
They form brightly coloured compounds — that green of copper, the orange of dichromate.
它们形成鲜艳的有色化合物——铜的那种绿色、重铬酸盐的橙色。
Many of them are excellent catalysts, like iron in the Haber process.
它们中许多是极好的催化剂， 比如哈伯法里的铁。
And they can have variable oxidation numbers: iron, for example, forms both iron two and iron three compounds.
而且它们可以有可变的氧化数：比如铁，既形成二价铁化合物， 也形成三价铁化合物。
These six beakers show why transition metals stand out in the lab.
这六只烧杯说明过渡金属在实验室为何显眼。
Each solution holds a different transition-metal ion, and each glows a different colour — red, orange, yellow, green, blue, purple.
每份溶液含有不同的过渡金属离子， 各自发出不同颜色——红、橙、黄、绿、蓝、紫。
Alkali metal compounds are usually white or colourless in solution; transition compounds paint the rack.
碱金属化合物在溶液中通常是白色或无色； 过渡化合物却把架子染成彩虹。
Remember the three other trademarks too: high density, high melting point, and often acting as a catalyst, either as the pure metal or in a compound.
还要记住另外三个标志：高密度、高熔点， 以及常作催化剂——可以是纯金属，也可以是化合物。
Coloured compounds plus catalysis plus variable oxidation numbers — that is the transition checklist.
有色化合物加催化加可变氧化数——这就是过渡元素清单。
Finally, the far right column: the noble gases.
最后，最右边的一列：稀有气体。
Helium, neon, argon.
氦、氖、氩。
They are the loners of chemistry — completely unreactive.
它们是化学中的独行者——完全不活泼。
They exist as single atoms, not as molecules.
它们以单个原子存在，而不是分子。
Why so unreactive?
为什么这么不活泼？
Because they already have a full outer shell of electrons.
因为它们已经有满的外层电子。
They are perfectly stable, with no need to gain, lose, or share any electrons.
它们非常稳定，不需要得到、失去或共用任何电子。
That stability is exactly what every other atom is reaching for when it reacts.
那种稳定， 正是其他每一个原子在反应时所追求的。
Pass electricity through a tube of each noble gas and it glows a characteristic colour — that is how neon signs and many display lights work.
让电流通过每种稀有气体的放电管，它会发出特有的颜色——霓虹灯和许多展示灯就是这样工作的。
Helium, neon, argon, krypton and xenon each have their own glow.
氦、氖、氩、氪和氙各有自己的光色。
They are monatomic gases: single atoms, not diatomic pairs like chlorine.
它们是单原子气体：单个原子， 不像氯那样成双原子对。
Unreactive because the outer shell is already full.
不活泼是因为外层已经满了。
That full shell is the stable electronic configuration every other atom is trying to reach by reacting.
那个满壳层正是其他原子通过反应想达到的稳定电子排布。
Noble gases already have it, so they stay alone.
稀有气体已经拥有它，所以它们独自存在。
Three marks to lock in.
锁住三个分。
First: the table is ordered by proton number; same group means same number of outer electrons, so similar reactions.
第一：表按质子数排列；同一族意味着相同数目的外层电子，所以反应相似。
Second: Group one gets more reactive going down, but Group seven gets less reactive — opposite trends.
第二：第一族往下越来越活泼，但第七族往下越来越不活泼——趋势相反。
Third: a more reactive halogen displaces a less reactive one; if it's the other way round, write no reaction.
第三：较活泼的卤素置换较不活泼的；如果反过来，就写没有反应。
Master these, and this topic is yours.
掌握这些，这个专题就是你的了。