How atoms bond - George Zaidan and Charles Morton

原子间是如何成键的- 乔治•扎依旦（George Zaidan） 和查尔斯•莫顿（Charles Morton）

翻译人员: Yolanda Zhang 校对人员: Xiaoou Chen

Most atoms don't ride solo,

大部分的原子不单独行动，

instead they bond with other atoms.

它们会跟其他原子发生键合。

And bonds can form between atoms

相同的原子间

of the same element

可以成键，

or atoms of different elements.

不同的原子也可以成键。

You've probably imagined bonding as a tug of war.

你可能会把成键的过程想象成拔河。

If one atom is really strong,

如果一个原子很强大，

it can pull one or more electrons

它就可以从另一个原子那里

off another atom.

拉拢来一个或者多个电子。

Then you end up with one negatively charged ion

这就能够得到一个带负点荷的离子

and one positively charged ion.

和一个带正电荷的离子。

And the attraction between these opposite charges

这种相反电荷间的吸引作用

is called an ionic bond.

就叫做离子键。

This is the kind of sharing

这种分配就类似于

where you just give away your toy to someone else

你把你的玩具给了别人，

and then never get it back.

就再也拿不回来了。

Table salt, sodium chloride,

食盐，也就是氯化钠，

is held together by ionic bonds.

就是通过离子键形成的。

Every atom of sodium gives up one electron

每一个钠原子将一个电子

to every atom of chlorine,

提供给一个氯原子，

ions are formed,

就形成了离子，

and those ions arrange themselves

这些离子排列形成了

in a 3D grid called a lattice,

一个三维的格子，叫做晶格，

in which every sodium ion

其中每一个钠离子跟

is bonded to six chloride ions,

6个氯离子成键，

and every chloride ion is bonded

每个氯离子又会跟

to six sodium ions.

6个钠离子成键。

The chlorine atoms never give

氯原子永远不会

the sodium atoms their electrons back.

将电子送返给钠原子。

Now, these transactions aren't always so cut-and-dried.

不过事实上，这种交易不总是这么清晰明朗。

If one atom doesn't completely overwhelm the other,

如果一个原子的吸电子能力并不是完全 凌驾于另一个原子之上，

they can actually share each other's electrons.

它们彼此之间就可以共用电子。

This is like a pot luck

这就像在家请客吃饭，

where you and a friend each bring a dish

你和朋友都准备了各自的菜肴，

and then both of you share both dishes.

这样你们就可以分享彼此的美食了。

Each atom is attracted to the shared electrons

每个原子都被

in between them,

共用的电子吸引，

and this attraction is called a covalent bond.

这种吸引作用就叫做共价键。

The proteins and DNA in our bodies,

打个比方，我们身体里的

for example,

蛋白质和DNA

are held together largely by these covalent bonds.

就是被共价键强力结合起来的。

Some atoms can covalently bond

一些原子只能与单独另一个原子

with just one other atom,

形成共价键，

others with many more.

而有很多原子可以形成多个共价键。

The number of other atoms

一个原子可以与多少其他原子

one atom can bond with

发生共价结合作用

depends on how its electrons are arranged.

取决于这些电子是如何排布的。

So, how are electrons arranged?

那么，这些电子到底是怎么排布的呢？

Every atom of a pure, unbonded element

一种单纯的，未发生键合的元素

is electrically neutral

的原子都是不带电荷的，

because it contains the same number

因为这种原子的原子核

of protons in the nucleus

携带了与核外电子

as it does electrons around the nucleus.

数目相同的质子。

And not all of those electrons are available for bonding.

不过不是所有的电子都可以成键。

Only the outermost electrons,

只有在最外层，

the ones in orbitals furthest from the nucleus,

在相距原子核最远的轨道上的电子，

the ones with the most energy,

携带的能量最多，

only those participate in bonding.

只有它们才能成键。

By the way, this applies to ionic bonding too.

不仅如此，离子键也是这种情况。

Remember sodium chloride?

还记得氯化钠吗？

Well, the electron that sodium loses

钠原子失掉的电子也是

is the one furthest from its nucleus,

离核最远的电子，

and the orbital that electron occupies

电子移向氯原子时

when it goes over to chlorine

所占据的轨道

is also the one furthest from its nucleus.

也是离核最远的。

But back to covalent bonding.

不过再回头来看共价键。

Carbon has four electrons

碳原子有4个电子

that are free to bond,

可以自由成键，

nitrogen has three,

氮原子有3个电子，

oxygen two.

氧原子有2个。

So, carbon is likely to form four bonds,

所以，碳原子可以形成4个键，

nitrogen three,

氮原子可以形成3个，

and oxygen two.

氧原子能形成2个。

Hydrogen only has one electron,

氢原子只有1个电子，

so it can only form one bond.

所以只能形成1个键。

In some special cases,

在某些特殊情况下，

atoms can form more bonds

原子可以违反常态的

than you'd expect,

形成更多的键，

but they better have a really good reason to do so,

不过通常都有些特殊的原因，

or things tend to fly apart.

或者物质发生了分解。

Groups of atoms

彼此间共用

that share electrons covalently with each other

电子的一组原子

are called molecules.

被称作分子。

They can be small.

分子可以很小。

For example, every molecule of oxygen gas

比方说，每一个氧气分子

is made up of just two oxygen atoms

都是通过2个氧原子

bonded to each other.

键合形成的。

Or they could be really, really big.

分子也可以非常，非常大。

Human chromosome 13 is just two molecules,

人类基因组13号只含有2个分子，

but each one has over 37 billion atoms.

不过每个分子都含有370亿个原子。

And this neighborhood,

这种聚合体，

this city of atoms,

庞大的原子群，

is held together by the humble chemical bond.

就是由不起眼儿的化学键连接形成的。