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HẸ SỐ 4 —CHza |
Fig. 1-10. The substance pictured Is œ-irone. |
1s an enormously complicated arrangement. nfortunately, we cannot picture |
all that is really known about it chemically, because the precise arrangement |
of all the atoms is actually known in three dimensions, while our picture is In |
only t§wo dimensions. The six carbons which form a rỉng do not form a fat ring, |
but a kind of “puckered” ring. All of the angles and distances are known. So a |
chemical ƒormula is merely a picture oŸ such a molecule. When the chemist writes |
such a thing on the blackboard, he is trying to “draw,” roughly speaking, in two |
dimensions. Eor example, we see a “ring” of six carbons, and a “chain” of carbons |
hanging on the end, with an oxygen second from the end, three hydrogens tied |
to that carbon, two carbons and three hydrogens sticking up here, etc. |
How does the chemist fnd what the arrangement is? He mixes bottles full of |
stuf together, and if it turns red, it tells him that it consists of one hydrogen |
and two carbons tied on here; 1Ý it turns blue, on the other hand, that is not |
the way it is at all. Thịis is one of the most fantastic pieces of detective work |
that has ever been done—organic chemistry. To discover the arrangement of the |
atoms in these enorrmously complicated arrays the chemist looks at what happens |
when he mixes two diferent substances together. The physicist could never quite |
believe that the chemist knew what he was talking about when he described |
the arrangement of the atoms. For about twenty years it has been possible, In |
some cases, to look at such molecules (not quite as complicated as this one, but |
some which contain parts of it) by a physical method, and it has been possible |
to locate every atom, not by looking at colors, but by rmeasuring tuhere theU qre. |
And lo and behold!, the chemists are almost aÌways correct. |
Tt turns out, in fact, that in the odor oŸ violets there are three slightly diferent |
mmolecules, which difÑfer only in the arrangement of the hydrogen atoms. |
One problem of chemistry is to name a substance, so that we will know what |
itis. Pind a name for this shapel Not only must the name tell the shape, but |
--- Trang 49 --- |
1 must also tell that here is an oxygen atom, there a hydrogen——exactly what |
and where each atom is. So we can appreciate that the chemical names must |
be complex In order to be complete. You see that the name of this thing In |
the more complete form that will tell you the structure of it is 4-(2, 2, 3, 6 |
tetramethy]-5-cyclohexeny])-3-buten-2-one, and that tells you that thìs is the |
arrangement. We can appreciate the difficulties that the chemists have, and also |
appreciate the reason for such long names. Ït is not that they wish to be obscure, |
but they have an extremely dificult problem in trying to describe the molecules |
in wordsl |
How do we knou that there are atoms? By one of the tricks mentioned earlier: |
we make the hựpothesis that there are atoms, and one after the other results come |
out the way we prediect, as they ought to 1ƒ things are made of atoms. There is |
also somewhat more direct evidence, a good example oŸ which is the following: |
The atoms are so small that you cannot see them with a light microscope——in |
fact, not even with an electron microscope. (With a light microscope you can |
only see things which are much bigger.) Now if the atoms are always in motion, |
say in water, and we put a big ball of something in the water, a ball much bigger |
than the atoms, the ball will jiggle around——much as in a push ball game, where |
a great big ball is pushed around by a lot of people. “The people are pushing in |
various directions, and the ball moves around the fñeld in an irregular fashion. |
So, in the same way, the “large ball” will move because of the inequalities of the |
collisions on one side to the other, from one moment to the next. Thherefore, if we |
look at very tiny particles (colloids) in water through an excellent microscope, we |
see a perpetual jiggling of the particles, which is the result of the bombardment |
of the atoms. This ¡is called the PBrounian rnotion. |
We can see further evidence for atoms in the structure of crystals. In many |
cases the structures deduced by x-ray analysis agree in their spatial “shapes” |
with the forms actually exhibited by crystals as they occur in nature. The angles |
between the various “faces” of a crystal agree, within seconds of arc, with angles |
deduced on the assumption that a crystal is made of many “layers” of atoms. |
ueruthing ¡s made öƒ atoms. That 1s the key hypothesis. The most important |
hypothesis ín all of biology, for example, is that cuerthing that animals do, atoms |
đo. In other words, (here ¡s nothing that liuứng thíngs do that cannot be wnderstood |
from the poin‡ oƒƑ uieuU that the are made oƒ atoms acting according to the lats |
öƒ phụsics. This was not known from the beginning: it took some experimenting |
and theorizing to suggest this hypothesis, but now it is accepted, and it is the |
mmost useful theory for producing new ideas in the fñeld of biology. |
--- Trang 50 --- |
TÝ a piece of steel or a piece of salt, consisting of atoms one next to the other, |
can have such interesting properties; iŸ water—which is nothing but these little |
blobs, mile upon mile of the same thing over the earth—can form waves and |
foam, and make rushing noises and strange patterns as it runs over cement; ïf all |
of this, all the life of a stream of water, can be nothing but a pile of atoms, hou |
tmuch more is possible? T instead oŸ arranging the atoms in some defñnite pattern, |
again and again repeated, on and on, or even forming little lumps of complexity |
like the odor of violets, we make an arrangement which is akh0øws đierent from |
place to place, with difÑferent kinds of atoms arranged in many ways, continually |
changing, not repeating, how much more marvelously is it possible that this thing |
might behave? Is it possible that that “thing” walking back and forth in front of |
you, talking to you, is a great glob of these atoms in a very complex arrangement, |
such that the sheer complexity of it staggers the imagination as to what it can |
do? When we say we are a pile of atoms, we do not mean we are merel a pile |
of atoms, because a pile of atoms which is not repeated from one to the other |
might well have the possibilities which you see before you in the mirror. |
--- Trang 51 --- |
M?qasic FPhạysữcs |
2-1 Introduction |
In this chapter, we shall examine the most fundamental ideas that we have |
about physics—the nature of things as we see them at the present time. We shall |
not discuss the history of how we know that all these ideas are true; you will |
learn these details in due time. |
'The things with which we concern ourselves in sclence appear in myriad forms, |
and with a multitude of attributes. Eor example, if we stand on the shore and |
look at the sea, we see the water, the waves breaking, the foam, the sloshing |
motion of the water, the sound, the air, the winds and the clouds, the sun and |
the blue sky, and light; there is sand and there are rocks of various hardness |
and permanence, color and texture. There are animals and seaweed, hunger and |
disease, and the observer on the beach; there may be even happiness and thought. |
Any other spot in nature has a similar variety of things and infuences. Ït is always |
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