What is the shape of a molecule? - George Zaidan and Charles Morton

分子是什麼形狀？- 喬治‧載登 (George Zaidan) 及查爾斯‧莫頓 (Charles Morton)

譯者: Helen Chang 審譯者: Regina Chu

分子長得什麼樣？

What is the shape of a molecule?

Well, a molecule is mostly empty space.

嗯... 分子裡面大部份是空空的

Almost all of its mass is concentrated

原子質量幾乎全都塞在

in the extremely dense nuclei of its atoms.

非常非常擠的原子核裡

And its electrons,

而電子

which determine how the atoms

則決定原子間的鍵結方式

are bonded to each other,

are more like clouds of negative charge

電子鍵比較像是

一整團電子雲

than individual, discrete particles.

而不是一顆顆單獨的粒子

So, a molecule doesn't have a shape

所以說，分子的形狀比較接近雲

in the same way that, for example,

而不像是... 一座雕像的形狀

a statue has a shape.

But for every molecule,

但對所有分子來說

there's at least one way

至少會有 1 種 排列原子核和電子的方式

to arrange the nuclei and electrons

so as to maximize the attraction

使相異電荷間的吸引力會最大

of opposite charges

and minimize the repulsion

而相同電荷間的互斥力會最小

of like charges.

Now, let's assume that the only electrons

假設只有最外圈的電子 會對分子的形狀產生影響

that matter to a molecule's shape

假設只有最外圈的電子 會對分子的形狀產生影響

are the outermost ones from each participating atom.

假設只有最外圈的電子 會對分子的形狀產生影響

And let's also assume

同時我們也假設

that the electron clouds in between atoms,

原子之間的電子雲 也就是分子鍵

in other words, a molecule's bonds,

原子之間的電子雲 也就是分子鍵

are shaped kind of like sausages.

形狀像一條熱狗

Remember that nuclei are positively charged

記得原子核是帶正電

and electrons are negatively charged,

電子則是帶負電

and if all of a molecule's nuclei

如果所有的原子核 都自己聚在一塊

were bunched up together

如果所有的原子核 都自己聚在一塊

or all of its electrons were bunched up together,

而所有的電子也都聚在一塊

they would just repel each other and fly apart,

它們會互相排斥而飛散

and that doesn't help anyone.

那就沒什麼用了

In 1776, Alessandro Volta,

1776 年，物理學家伏特

decades before he would eventually invent batteries,

他在發明電池的數十年前

discovered methane.

先是發現了甲烷 (Methane)

Now, the chemical formula of methane is CH4.

甲烷的分子式是 CH4

And this formula tells us

這個分子式告訴我們 每個甲烷分子裡面

that every molecule of methane

這個分子式告訴我們 每個甲烷分子裡面

is made up of one carbon and four hydrogen atoms,

含有 1 個碳原子和 4 個氫原子

but it doesn't tell us what's bonded to what

但從分子式卻看不出來 誰和誰相互鍵結

or how they atoms are arranged in 3D space.

也看不出這些原子 在空間中的排列方式

From their electron configurations,

從碳的電子組態可知

we know that carbon can bond

碳原子最多可以連結 四個以上的原子

with up to four other atoms

and that each hydrogen can only bond

而每個氫原子 則只能連接一個原子

with one other atom.

而每個氫原子 則只能連接一個原子

So, we can guess

所以，我們可以推論

that the carbon should be the central atom

碳原子應該是中心原子 以和其他氫原子相結合

bonded to all the hydrogens.

Now, each bond represents

每個鍵結即代表兩個共用電子

the sharing of two electrons

and we draw each shared pair of electrons as a line.

每對共用電子對則用線段表示

So, now we have a flat representation

現在我們可以畫出 這個分子的平面圖

of this molecule,

but how would it look in three dimensions?

但在空間中看起來是如何呢？

We can reasonably say

合理的說

that because each of these bonds

每個鍵結都代表著 帶有負電荷的範圍

is a region of negative electric charge

and like charges repel each other,

正因為同性相斥

the most favorable configuration of atoms

原子最喜歡的排列組態

would maximize the distance between bonds.

是每個鍵結離得越遠越好

And to get all the bonds

所以，要讓所有鍵結離得最遠

as far away from each other as possible,

所以，要讓所有鍵結離得最遠

the optimal shape is this.

最理想的形狀，就會變成這樣

This is called a tetrahedron.

我們稱為：四面體

Now, depending on the different atoms involved,

如果含有不同的原子

you can actually get lots of different shapes.

形狀也多有不同

Ammonia, or NH3, is shaped like a pyramid.

例如：氨 NH3 是金字塔形

Carbon dioxide, or CO2, is a straight line.

二氧化碳 CO2 則是一直線

Water, H2O, is bent like your elbow would be bent.

水 H2O 形狀有點像彎折的手臂

And chlorine trifluoride, or ClF3,

三氟化氯 ClF3 形狀則像是一個英文字母 T

is shaped like the letter T.

三氟化氯 ClF3 形狀則像是一個英文字母 T

我們現在是要 建立原子和電子的3D排列模型

Remember that what we've been doing here

is expanding on our model of atoms and electrons

to build up to 3D shapes.

We'd have to do experiments

我們還是要做實驗 看看這些分子實際上的形狀

to figure out if these molecules

actually do have the shapes we predict.

是不是和我們想的一樣

Spoiler alert:

答案提示：

most of the do, but some of them don't.

大部份是對的，但有些錯了

Now, shapes get more complicated

如果原子數增加了 形狀當然也跟著變複雜

as you increase the number of atoms.

如果原子數增加了 形狀當然也跟著變複雜

All the examples we just talked about

我們剛剛舉的例子

had one obviously central atom,

都有一個明確的中心原子

but most molecules,

但大部分的分子

from relatively small pharmaceuticals

從醫藥等級的小分子

all the way up to long polymers

到又臭又長的 DNA 或蛋白質 等高分子聚合物

like DNA or proteins, don't.

都沒有中心分子

The key thing to remember

is that bonded atoms will arrange themselves

重要的是 原子鍵結它們會自己排好

to maximize the attraction between opposite charges

依據法則

同性相斥最遠 異性相吸最近

and minimize the repulsion between like charges.

找到最合適的排列組態

Some molecules even have two or more

有些分子甚至 有兩種以上的安定組態

stable arrangements of atoms,

and we can actually get really cool chemistry

變換不同的組態 就會產生很多很酷的化學現象

from the switches between those configurations,

even when the composition of that molecule,

即便是分子成份不變 即其中的原子種類、原子數目

that's to say the number and identity of its atoms,

has not changed at all.

沒有改變