These are of two varieties, known as single and double bonds.

化学键有两种，单键和双键。

It's made of a polymer called " polyethylene terephthalate" , which has rings of carbons separated by chains of carbons, some of which have single and double bonds, to oxygen atoms.

它是由聚对苯二甲酸乙二醇酯聚合的，它有分离的碳链，相对于氧原子而言，一些含有单键和双键。

Carboxylic acids are a type of organic compound characterized by a carbon (C) atom doubly bonded to an oxygen (O) atom and singly bonded to a hydroxyl group (-OH) .

羧酸是一种有机化合，其特征是一碳（C）原子与一氧（O）原子双键结合，并与一羟基（-OH）单键结合。

Interestingly enough, there's actually no back or menu buttons.

有趣的是，实际上并没有返回键或菜单键。

Certain reactions open up a double or triple bond to insert various atoms, leaving only a single bond between the carbons. These are called addition reactions, because atoms are added to the carbons that were previously double bonded.

某些反应会打开双键或三键，从而插入各种原子，使碳原子之间单键。这类反应称为加反应，因为原子被添加到了原先以双键相连的碳原子上。

The chains are held together by bonds between the carbon atoms. These are of two varieties known as single and double bonds.

这些链通过碳原子之间的键连接在一起。这些键有两种类型，分别是单键和双键。

Single bonds, also called sigma bonds, are pretty simple, and carbon atoms attached by them can rotate around the bond freely.

单键，也称为σ键，非常简单，通过它们连接的碳原子可以自由地围绕该键旋转。

Gone is the sort of back and the menu buttons previously present on most Android phones, and simply swiping across this opens up multitasking, and tapping on it once will take you back.

华为P10的机身背部和大多数安卓手机上的菜单键都消失了，只需轻轻一划就能打开多任务处理界面，轻点一下即可返回。

So, three words representing three different groups of organic compounds. Alkanes for all single bonds, alkenes if they contain double bonds, and alkynes if they contain one or more triple bonds.

因此，这三词分别代表三类不同的有机化合。烷烃是指所有键均为单键的化合；烯烃是指含有双键的化合；炔烃是指含有一或多三键的化合。

Certain reactions open up a double or triple bond to insert various atoms, leaving only a single bond between the carbons.

某些反应会打开双键或三键，在碳原子之间插入各种原子，最终下单键。

Now, the bonds in alkenes have a few tricks up their sleeves, not as simple as you might imagine. Single bonds, also called sigma bonds, are pretty simple, and carbon atoms attached by them can rotate around the bond freely.

现在，烯烃中的键有一些复杂之处，并不像你可能想象的那样简单。单键，也称为σ键，相当简单，通过它们连接的碳原子可以自由地绕键旋转。

But once that's done, the hydrogen atoms readily attach to the hydrocarbon molecule, converting a double bond to a single bond.

但一旦完这一步，氢原子就会很容易地附着到碳氢化合分子上，将双键转化为单键。

So three words representing three different groups of organic compounds: alkanes for all single bonds, alkenes if they contain double bonds, and alkynes if they contain one or more triple bonds.

所以三词代表三种不同的有机化合：烷烃表示全单键，烯烃表示含有双键，炔烃表示含有一或多三键。