来自《耶鲁大学开放课程：新生有机化学第2集第2集》

because we don't know how it works,

我们并不知道化学键的原理
we don't know what it really is.

我们不知道它到底是什么
So can we find out what it really is?

我们能不能揭开它的真面目呢
Well in the nineteenth century they discovered bonds.

19世纪的人们发现了化学键的存在
And this is a picture from 1861, we'll talk about this later.

我们稍后会谈到这张1861年的图
It's one of the first depictions that's recognizable

这是对于今日人们所知的
by people today of bonds between atoms.

化学键的最早的描述
So there are different numbers of these lines,

不同的原子间的线
valences, for different atoms.

即化学价的数目不同
Hydrogen has one; carbon has four;

氢原子是一价碳原子是四价
oxygen two; nitrogen three.

氧二价氮三价
Why do the elements differ?

不同元素的化学价为何不同呢