1–3Atomic processes 原子的过程

Figure 1–5 图1–5 水在空气中蒸发
So much for the description of solids,liquids, and gases from the atomic point of view. However, the atomichypothesis also describes processes, and so we shall now look at anumber of processes from an atomic standpoint. The first process that we shalllook at is associated with the surface of the water. What happens at the surfaceof the water? We shall now make the picture more complicated—and more realistic—byimagining that the surface is in air. Figure 1–5 showsthe surface of water in air. We see the water molecules as before, forming abody of liquid water, but now we also see the surface of the water. Above thesurface we find a number of things: First of all there are water molecules, asin steam. This is water vapor, which is always found above liquid water.(There is an equilibrium between the steam vapor and the water which will bedescribed later.) In addition we find some other molecules—here two oxygenatoms stuck together by themselves, forming an oxygen molecule, theretwo nitrogen atoms also stuck together to make a nitrogen molecule. Airconsists almost entirely of nitrogen, oxygen, some water vapor, and lesseramounts of carbon dioxide, argon, and other things. So above the water surfaceis the air, a gas, containing some water vapor. Now what is happening in thispicture? The molecules in the water are always jiggling around. From time totime, one on the surface happens to be hit a little harder than usual, and getsknocked away. It is hard to see that happening in the picture because it is a stillpicture. But we can imagine that one molecule near the surface has just beenhit and is flying out, or perhaps another one has been hit and is flying out.Thus, molecule by molecule, the water disappears—it evaporates. But if we closethe vessel above, after a while we shall find a large number of molecules ofwater amongst the air molecules. From time to time, one of these vapormolecules comes flying down to the water and gets stuck again. So we see thatwhat looks like a dead, uninteresting thing—a glass of water with a cover, thathas been sitting there for perhaps twenty years—really contains a dynamic andinteresting phenomenon which is going on all the time. To our eyes, our crudeeyes, nothing is changing, but if we could see it a billion times magnified, wewould see that from its own point of view it is always changing: molecules areleaving the surface, molecules are coming back.
从原子的观点出发，我们对固体、液体和气体的描述，已经有了很多。然而，原子的假设，也同样描述了若干过程，所以，我们将从原子的观点出发，看看这些过程。我们要看的第一个过程，是与水的表面有关的。在水的表面，究竟发生了什么呢？我们现在，通过想象表面是在空气中的，而让这幅图，变得更复杂和更接近实际。图1-5就显示了在空气中的水的表面。正如以前一样，我们看到水分子，它形成了水体，但是，现在我们也看到了水的表面。在水面上方，我们发现了若干事物，首先，有水分子作为蒸汽。这就是水蒸汽，它总是出现在液体水的上方。（在水蒸汽和水之间，有一种平衡，后面将会讲它。）另外，我们还发现了一些其它分子，这里，两个氧原子连在一起，形成一个氧分子；那里，两个氢原子连在一起，形成一个氢分子。空气几乎完全是由氮气、氧气、一些水蒸气、少量的二氧化碳，氩气、和其他事物构成。所以，在水面上方，就是空气、瓦斯包含一些水蒸气。现在，在这幅图中，究竟发生了什么呢？水中的分子，总是在不停地轻摇。时不时地，水表面的一个分子，就会冲的比平常厉害一点，结果就冲了出去。在这个图中，很难看出这种情况，因为图是静态的。但是，我们完全可以想象，一会儿这个分子被撞的飞了出去，一会儿那个被撞的飞了出去。这样逐渐地，一个分子一个分子地，水就消失了—它蒸发了。但是如果我们把容器的上方封闭起来，那么，过一会儿，我们就会发现，在空气的分子中，有大量的水分子。时不时的，这些空气中的水分子，又会飞向水面，再次被水抓住。这样。我们就明白了，一杯带盖子的水，在那里有可能已经20年了，看上去死气沉沉，毫无生趣，而实际上呢，它却包含着一个动态的和有趣的现象，且一直在发生着。对于我们的眼睛、我们粗糙的眼睛来说，什么也没有改变，但是，如果们把它放大十亿倍，从水的角度来看，它就是不停地在变化，分子不断地离开表面，又不断地回来。

Why do we see no change?Because just as many molecules are leaving as are coming back! In the long run “nothinghappens.” If we then take the top of the vessel off and blow the moist air away,replacing it with dry air, then the number of molecules leaving is just thesame as it was before, because this depends on the jiggling of the water, butthe number coming back is greatly reduced because there are so many fewer watermolecules above the water. Therefore there are more going out than coming in,and the water evaporates. Hence, if you wish to evaporate water turn on thefan!
为什么我们看不到变化？因为离开的分子，与回来的分子一样多，所以从长远看，“什么也没发生”。因此，如果我们把容器上方的盖子去掉，把湿空气吹掉，用干空气替代，那么，离开的分子，与以前一样多，因为这依赖于水的轻摇，但是，回来的则大幅度地减少，因为水上方的水分子很少了。所以，走的多，回来的少，水蒸发了。因此，如果你希望蒸发水的话，把电扇打开。

Here is something else: Which moleculesleave? When a molecule leaves it is due to an accidental, extra accumulation ofa little bit more than ordinary energy, which it needs if it is to break awayfrom the attractions of its neighbors. Therefore, since those that leave havemore energy than the average, the ones that are left have less averagemotion than they had before. So the liquid gradually cools if itevaporates. Of course, when a molecule of vapor comes from the air to the waterbelow there is a sudden great attraction as the molecule approaches thesurface. This speeds up the incoming molecule and results in generation ofheat. So when they leave they take away heat; when they come back they generateheat. Of course when there is no net evaporation the result is nothing—the wateris not changing temperature. If we blow on the water so as to maintain a continuouspreponderance in the number evaporating, then the water is cooled. Hence, blowon soup to cool it!
这里还有些其他事情：哪个分子会离开呢？当一个分子离开的时候，那是由于它所积累的能量，比通常的能量，要多一点，这个能量积累的过程是偶然的，如果这个分子要挣脱其邻居的吸引力，它就需要这份能量。所以，由于那些离开的分子所具有的能量，比平均值多，所以，剩下的分子所具有的能量，就会比以前少。于是，如果液体蒸发的话，它就会逐渐变冷。当然，当一个蒸汽中的分子，从空气中，来到其下面的水中时，由于分子在接近水面时，会产生一个突然的巨大的吸引力。这会给落到水中的这个分子加速，并导致热量的产生。所以，分子离开时，带走热量；分子回来时，产生热量。当然，当没有净蒸发时，结果就不变，即水温不变。如果我们在水上吹，以让蒸发的数量，保持连续的优势，那么水就变凉了。因此。把汤吹吹，可以让它变凉。

Of course you should realize that theprocesses just described are more complicated than we have indicated. Not onlydoes the water go into the air, but also, from time to time, one of the oxygenor nitrogen molecules will come in and “get lost” in the mass of watermolecules, and work its way into the water. Thus the air dissolves in thewater; oxygen and nitrogen molecules will work their way into the water and thewater will contain air. If we suddenly take the air away from the vessel, thenthe air molecules will leave more rapidly than they come in, and in doing so willmake bubbles. This is very bad for divers, as you may know.
当然你应该意识到，我们上面所描述的这个过程，实际上可能更复杂。不仅水会变成空气，同时不断地有氧分子，或者氢分子，会“消失”在巨大的水分子中，以它们的方式融入水中。这样空气就会溶解在水中，氧分子和氢分子将会以它们的方式，融入水中，水将包含空气。如果我们把容器中的空气突然拿掉，那么离开的空气分子，将比到来的更多，这样，就会产生气泡。如你所知，这对潜水员来说非常糟糕。

Figure 1–6 盐溶解于水中


Figure 1–7
Now we go on to another process. In Fig. 1–6 we see,from an atomic point of view, a solid dissolving in water. If we put a crystalof salt in the water, what will happen? Salt is a solid, a crystal, anorganized arrangement of “salt atoms.” Figure 1–7 is anillustration of the three-dimensional structure of common salt, sodium chloride.Strictly speaking, the crystal is not made of atoms, but of what we call ions.An ion is an atom which either has a few extra electrons or has lost a fewelectrons. In a salt crystal we find chlorine ions (chlorine atoms with anextra electron) and sodium ions (sodium atoms with one electron missing). Theions all stick together by electrical attraction in the solid salt, but when weput them in the water we find, because of the attractions of the negativeoxygen and positive hydrogen for the ions, that some of the ions jiggle loose.In Fig. 1–6we see a chlorine ion getting loose, and other atoms floating in the water inthe form of ions. This picture was made with some care. Notice, for example,that the hydrogen ends of the water molecules are more likely to be near thechlorine ion, while near the sodium ion we are more likely to find the oxygenend, because the sodium is positive and the oxygen end of the water isnegative, and they attract electrically. Can we tell from this picture whetherthe salt is dissolving in water or crystallizing out of water? Ofcourse we cannot tell, because while some of the atoms are leaving thecrystal other atoms are rejoining it. The process is a dynamic one, justas in the case of evaporation, and it depends on whether there is more or lesssalt in the water than the amount needed for equilibrium. By equilibrium wemean that situation in which the rate at which atoms are leaving just matches therate at which they are coming back. If there is almost no salt in the water,more atoms leave than return, and the salt dissolves. If, on the other hand,there are too many “salt atoms,” more return than leave, and the salt iscrystallizing.
现在我们去看另外一个过程。在图1-6中，我们从原子的观点出发，看到了水中固体的溶解。如果我们把结晶盐放入水中，会发生什么呢？盐是“盐原子”的固体结晶，很有组织。普通的盐就是氯化钠。图1-7就是这种盐的的三维结构的示意图。严格地说，这个晶体不是由原子构成的，而是由我们称为离子的东西构成的。一个原子，多了几个额外的电子，或者失去了几个电子，就被称为离子。在一个盐的晶体中，我们发现氯离子（氯原子多带一个电子），和钠离子（钠原子失去一个电子）。在固体盐中，所有的离子，由于电子吸引力而相互粘在一起，但是当我们把它们放入水中的时候，我们发现，由于负氧离子的作用和正氢离子的作用，有些离子逐渐松动了。在图1-6中，我们看到一个氯离子松动了，而其他原子，则以离子的形式浮出了水面。这个图片制作时，还是很精心地。例如，可注意到，水分子的氢端，更接近氯离子，而靠近钠离子，我们会发现氧端，因为钠是正的，而水的氧端是负的，由于电子作用，它们相互吸引。从这张图中，我们能否得出，盐究竟是在水中溶解，还是从水中结晶出来呢？当然我们不能，因为当有些原子离开它时，有些原子会重新加入它。这个过程是动态的，正如蒸发的情况一样；并且，它也依赖于，水中盐的含量，与达到平衡所需的量相比，究竟是多还是少。所谓平衡，我们是指这样一种情况，在其中，原子离开的比率与原子回来的比率想匹配。如果水中基本没盐，原子离开的多回来的少，则盐溶解。相反，如果水中有太多的“盐原子”，回来的多，离开的少，则盐结晶。

In passing, we mention that the concept ofa molecule of a substance is only approximate and exists only for acertain class of substances. It is clear in the case of water that the threeatoms are actually stuck together. It is not so clear in the case of sodium chloridein the solid. There is just an arrangement of sodium and chlorine ions in a cubicpattern. There is no natural way to group them as “molecules of salt.”
Returning to our discussion of solution andprecipitation, if we increase the temperature of the salt solution, then the rateat which atoms are taken away is increased, and so is the rate at which atomsare brought back. It turns out to be very difficult, in general, to predictwhich way it is going to go, whether more or less of the solid will dissolve.Most substances dissolve more, but some substances dissolve less, as the temperatureincreases.
顺便说说，对于一种实质体来说，它的分子的概念，只是近似的，而且，这只是对某些种类的实质体来说，才是存在的。在水的情况下，很清楚，三个原子是粘在一起的。在固体氯化钠的情况下，就不是这么清楚了。在一个立方体中，钠离子和氯离子如何安排，就是一个问题。并没有一种自然的方式，可以把它们作为“盐的分子”来分组。回到我们关于溶解和凝结的讨论中，如果我们增加盐溶液的温度，那么，原子被拿掉的速率就会增加，原子被带回来的速率也如此。所以，一般来说，要预测事情究竟像会向哪个方向发展、即固体究竟溶解的多还是少，比较困难。随着温度的增加，大多数实质体，溶解的多，少数实质体，溶解的少。

1–4Chemical reactions 化学反应
In all of the processes which have been describedso far, the atoms and the ions have not changed partners, but of course thereare circumstances in which the atoms do change combinations, forming new molecules.This is illustrated in Fig. 1–8. A processin which the rearrangement of the atomic partners occurs is what we call a chemicalreaction. The other processes so far described are called physical processes,but there is no sharp distinction between the two. (Nature does not care whatwe call it, she just keeps on doing it.) This figure is supposed to representcarbon burning in oxygen. In the case of oxygen, two oxygen atoms sticktogether very strongly. (Why do not three or even four sticktogether? That is one of the very peculiar characteristics of such atomic processes.Atoms are very special: they like certain particular partners, certainparticular directions, and so on. It is the job of physics to analyze why eachone wants what it wants. At any rate, two oxygen atoms form, saturated and happy,a molecule.)
迄今为止，我们讲了很多过程，在其中，原子和离子确实没有更换其搭档，但是，确实有这么一些情况，在其中，原子改变了其组合，形成了新的分子。如图1-8所示。一个过程，如果在其中，原子的搭档被重新安排了，那么，我们就称其为化学反应。迄今为止，我们所讲的其他过程，则被称为物理过程，但是，这两种过程之间的区别，并非泾渭分明。（自然并不在乎我们如何称呼它，她只是不断的在做这个事情）。这个图，被认为是碳在氧中燃烧。在氧的情况，两个氧原子紧密地连在一起。（为什么不是三个或四个原子连在一起呢？这是这类原子过程的一个非常独特的属性。原子很特别，他们喜欢某些独享的搭档、某些独享的方向，如此等等。为什么原子喜欢这样，分析它，正是物理学的工作。不管速率如何，两个氧原子形成了一个分子，达到饱和，且很愉快。）

Figure 1–8 图 1–8 碳在氧中燃烧

The carbon atoms are supposed to be in a solidcrystal (which could be graphite or diamond1).Now, for example, one of the oxygen molecules can come over to the carbon, andeach atom can pick up a carbon atom and go flying off in a new combination—“carbon-oxygen”—whichis a molecule of the gas called carbon monoxide. It is given the chemical nameCO. It is very simple: the letters “CO” are practically a picture of that molecule.But carbon attracts oxygen much more than oxygen attracts oxygen or carbonattracts carbon. Therefore in this process the oxygen may arrive with only a littleenergy, but the oxygen and carbon will snap together with a tremendous vengeanceand commotion, and everything near them will pick up the energy. A large amountof motion energy, kinetic energy, is thus generated. This of course is burning;we are getting heat from the combination of oxygen and carbon. The heatis ordinarily in the form of the molecular motion of the hot gas, but in certaincircumstances it can be so enormous that it generates light. That is howone gets flames.
碳原子被认为是在固态晶体中（它们可能是石墨或钻石）。现举例如下，一个氧分子，来到碳跟前，其中的每个氧原子，选一个碳原子，然后，以一种新的组合—“碳氧”--飞走了，这就是空气中的一种分子，被称为一氧化碳。其化学名称为CO。它很简单：字母“CO”实际上就是这个分子的图像。但是，碳与氧之间的吸引力，要比氧与氧和碳与碳之间的都大。所以，在这个过程中，氧到来的时候，可能只带着一点点能量，但是养和碳，会啪的一下，猛咬在一起，像巨大的复仇和骚乱，其附近的所有东西，都会增加一些能量。大量的运动能量，即动能，就是这样产生的。这当然就是燃烧；我们从氧与碳的结合中，获得热量。热量通常是在热空气的分子运动这一形式中，但是，在某些情况下，热量巨大，以至于会产生光。人们就是这样得到火焰的。

In addition, the carbon monoxide is notquite satisfied. It is possible for it to attach another oxygen, so that we mighthave a much more complicated reaction in which the oxygen is combining with thecarbon, while at the same time there happens to be a collision with a carbonmonoxide molecule. One oxygen atom could attach itself to the CO and ultimatelyform a molecule, composed of one carbon and two oxygens, which is designated CO2and called carbon dioxide. If we burn the carbon with very little oxygenin a very rapid reaction (for example, in an automobile engine, where theexplosion is so fast that there is not time for it to make carbon dioxide) aconsiderable amount of carbon monoxide is formed. In many such rearrangements, avery large amount of energy is released, forming explosions, flames, etc.,depending on the reactions. Chemists have studied these arrangements of the atoms,and found that every substance is some type of arrangement of atoms.
另外，一氧化碳并不完全满足。对它来说，完全可能吸引另外一个氧原子，这样，我们就可以有一个复杂的多的反应，在其中，氧与碳结合，同时，还有一个氧原子与一氧化碳分子的碰撞。一个氧原子可以把它自己，附加给CO，最终形成一个分子，由一个碳两个氧组成，它被标识为CO2，称为二氧化碳。如果在一个非常快的反应中，我们燃烧碳与非常少的氧（例如，在汽车发动机中，那里爆炸是如此之快的，几乎没有时间让其形成二氧化碳），那么，相当数量的一氧化碳，就会形成。在很多这种重新排列中，会释放大量的能量，形成爆炸、火焰等等，这随反应类型而定。化学家研究了这些原子的排列，发现每种实质体，其实都是某种原子排列的类型。

To illustrate this idea, let us consideranother example. If we go into a field of small violets, we know what “that smell”is. It is some kind of molecule, or arrangement of atoms, that hasworked its way into our noses. First of all, how did it work its way in?That is rather easy. If the smell is some kind of molecule in the air, jigglingaround and being knocked every which way, it might have accidentally workedits way into the nose. Certainly it has no particular desire to get into ournose. It is merely one helpless part of a jostling crowd of molecules, and inits aimless wanderings this particular chunk of matter happens to find itselfin the nose.
为了说明这个想法，让我们考虑另一个例子。如果我们走到一片紫罗兰地里，我们知道“那个味道”是什么？它就是某种分子，或者说是某种原子的排列，想办法钻进了我们的鼻子。它最初是如何做到的呢？这很容易。如果这个气味，是空气中的某种分子，不断轻摇，并被撞向四面八方，那么，完全可能，它只是偶然地钻进了我们的鼻子。当然它并不是出于某种特别的欲望，要进入我们的鼻子。它只是空气中的诸分子的一部分，这些分子，挤在一起，无助地乱撞着，这堆特别的物质，在其毫无目的的游荡中，碰巧发现，它在我们的鼻子里。

How does the chemist find what the arrangementis? He mixes bottles full of stuff together, and if it turns red, it tells himthat it consists of one hydrogen and two carbons tied on here; if it turnsblue, on the other hand, that is not the way it is at all. This is one of themost fantastic pieces of detective work that has ever been done—organic chemistry.To discover the arrangement of the atoms in these enormously complicated arraysthe chemist looks at what happens when he mixes two different substances together.The physicist could never quite believe that the chemist knew what he was talkingabout when he described the arrangement of the atoms. For about twenty years ithas been possible, in some cases, to look at such molecules (not quite as complicatedas this one, but some which contain parts of it) by a physical method, and ithas been possible to locate every atom, not by looking at colors, but by measuringwhere they are. And lo and behold!, the chemists are almost always correct.
排列是什么样的，化学家又是如何发现的呢？他把瓶子里塞满东西，如果瓶子变红，那么，它就是由一个氢二个碳组成，如果瓶子变蓝，那么相反，它就不是这样。曾经的探测工作，就是这样，叫有机化学；这个方法，是最异想天开的探测方法之一。要在这些巨复杂的阵列中，发现原子的排列，化学家们要去查看：当他把两种不同的实质体，混合在一起的时候，会发生什么。化学家们说他们知道分子的排列，对此，物理学家们永远也不会相信。因为在有些情况下，通过物理的方法来查看分子的结构（不像这个这么复杂，而是某种包含着其一部分的分子），已经有20年了，而且，不是通过颜色，而是通过计算，得到分子的位置，在他们那里是可能的。你瞧！，化学家们几乎总是正确的。

It turns out, in fact, that in the odor ofviolets there are three slightly different molecules, which differ only in thearrangement of the hydrogen atoms.
事实就是，在紫罗兰的气味中，有三种分子，其区别很少，即只在于氢原子的排列。

One problem of chemistry is to name a substance,so that we will know what it is. Find a name for this shape! Not only must thename tell the shape, but it must also tell that here is an oxygen atom, there ahydrogen—exactly what and where each atom is. So we can appreciate that thechemical names must be complex in order to be complete. You see that the name ofthis thing in the more complete form that will tell you the structure of it is4-(2, 2, 3, 6 tetramethyl-5-cyclohexenyl)-3-buten-2-one, and that tells you thatthis is the arrangement. We can appreciate the difficulties that the chemists have,and also appreciate the reason for such long names. It is not that they wish tobe obscure, but they have an extremely difficult problem in trying to describethe molecules in words!
化学的问题之一，就是给一个实质体命名，这样，我们就会知道它是什么。为这个形状，找到一个名字！这个名字，不仅要告知形状，而且，要清楚地告知，每个原子在哪里：这里一个氧原子，那里一个氢原子等等。于是，我们就应该认同，化学的名称，就应该是复杂的，以便完整。你可以看到，这个东西的名称，处于非常更复杂的形式中，它将告知其结构，就是：4-(2, 2, 3, 6 tetramethyl-5-cyclohexenyl)-3-buten-2-one，这个名称告诉你，这就是排列。我们可以认同化学家所遭遇的困难，也可以认同长名字的原因。如此朦胧，并非他们的本意，乃是因为，在用单词来把分子描述清楚时，会遭遇到巨大的困难。

How do we know that there are atoms?By one of the tricks mentioned earlier: we make the hypothesis that thereare atoms, and one after the other results come out the way we predict, as theyought to if things are made of atoms. There is also somewhat more directevidence, a good example of which is the following: The atoms are so small thatyou cannot see them with a light microscope—in fact, not even with an electronmicroscope. (With a light microscope you can only see things which are muchbigger.) Now if the atoms are always in motion, say in water, and we put a bigball of something in the water, a ball much bigger than the atoms, the ballwill jiggle around—much as in a push ball game, where a great big ball ispushed around by a lot of people. The people are pushing in various directions,and the ball moves around the field in an irregular fashion. So, in the sameway, the “large ball” will move because of the inequalities of the collisionson one side to the other, from one moment to the next. Therefore, if we look atvery tiny particles (colloids) in water through an excellent microscope, we seea perpetual jiggling of the particles, which is the result of the bombardment ofthe atoms. This is called the Brownian motion.
我们如何知道有原子的呢？通过上面所说的诀窍之一，我们做出有原子的假设，照此预测，得到了一系列的结果：如果事物是由原子构成的，结果就应该如此。当然，还有一些更直接的证据，其中一个好的例子如下：原子是如此之小，以至于你不可能用一个光学显微镜看到它们，事实上，甚至不能用一个电子显微镜看到。（用一个光学显微镜，你只能看到一些比原子要大的多的东西。）现在，如果原子总是处于运动中，以水为例，我们在水中放一个大的球一样的东西，这个球，比原子要大得多，那么，这个球就会不断地在晃动，正如在推球游戏中，一个大球，被很多人在推。由于人们推球时，是往不同的方向推，所以这个球，就在那个地方做着不规则的运动。于是，以同样的方式，水中的这个“大球”，将会由于在各个方向、各个时间的不平衡的撞击，而移动。因此，如果我们通过一个杰出的显微镜，来看水中的非常小的粒子（胶质），就会看到这些粒子的永久晃动，这就是原子轰击的结果。这我们称之为布朗运动。