How polarity makes water behave strangely - Christina Kleinberg

Transcriber: Andrea McDonough Reviewer: Bedirhan Cinar

翻译人员: Gabriella Hu 校对人员: 易帆 余

How come some insects are able to walk

为什么有些昆虫可以

on the surface of a pond,

在水面上轻轻拂过，

but you quickly sink to the bottom

但是当你试图踏入水中时

when you try to walk on water?

却立即沉入水底？

And why do lakes freeze from the top down in winter?

为什么湖水结冰时从水面开始往下结冰呢？

In a word, the answer to all these questions is polarity.

简单地说，以上所有问题的答案都是极性

Water is a simple molecule

水是一种简单的分子

made up of one oxygen atom and two hydrogen atoms,

是由一个氧原子和两个氢原子组成的，

but it is essential to life.

但水仍然是生命之源

In fact, water makes up approximately 60%

事实上，一个成年人60%的体重

of the adult human being's body weight.

都是由水组成的

The polarity within those water molecules

这些水分子的极性

gives this common substance the properties

给予了这个简单的物质

that make it unique and life-sustaining.

独特且能够维持生命的性质

Polarity refers to the unequal sharing

极性指的是一个分子内

of electrons within a molecule.

电荷分布的不均匀性

For water, the bonding between the oxygen atom

对水来说，在一个水分子中

and two hydrogen atoms within a single water molecule

氧原子和两个氢原子之间的化学键

is like a tug-of-war between a big, strong football player

就像一个高大强壮的足球运动员和

and a cute little toddler.

一个可爱的婴儿之间进行拔河

Oxygen is a larger atom,

氧原子更大一些，

with more protons in its nucleus than hydrogen.

它的原子核中比氢原子有更多的质子

These positive charges are like a person's physical strength.

这些正电荷就像一个人的力气一样

They're able to attract

它们能够吸引

the negatively charged electrons in the bond,

带负电荷的电子，

just like a strong individual is able to overpower

就像较强的一方可以在拔河比赛中

a weaker individual in a tug of war.

战胜较弱的一方

So, oxygen is able to attract

所以，氧原子能够比氢原子

more than its fair share of electrons.

吸引更多的电子

Because hydrogen is smaller and has less strength,

因为氢原子体积小，有更小的力量，

or fewer protons,

更少的质子，

it loses the tug of war

它在拔河比赛中输了，

and attracts fewer than its fair share of electrons.

于是就比氧原子吸引更少的电子

So, the oxygen in water behaves as though it's negative,

水当中的氧原子带负电，

and the hydrogens behave as though they're positive.

氢原子带正电

The bonds within a single water molecule

一个水分子中的化学键

are called polar covalent bonds.

叫做极性共价键

Covalent means that the electrons are shared.

共价代表电子由两个原子共有

But, as we just learned,

但是，正如我们刚才所学的，

polar means that these electrons are not shared equally.

极性表示电子不是均匀分布的，

In water, the oxygen acts negative

在水分子中，氧原子是带负电的

and the hydrogens act positive.

而氢原子是带正电的

Since negative and positive attract,

异电性物质相互吸引，

that oxygen is attracted to the hydrogen atoms

所以氧原子和氢原子在不同的

in neighboring water molecules.

水分子之间相互吸引

A special type of bond forms between water molecules,

水分子之间产生了一种特殊的化学键，

known as a hydrogen bond.

叫做氢键

Hydrogen bonds don't just happen in water either.

氢键不只是在水分子之间存在

They can form between a water molecule

也可以在水分子和

and different substances that are polar or ionic.

不同的极性分子或者离子化合物之间存在

Water's ability to stick to itself is called cohesion,

水分子能够簇在一起，这叫做凝聚力，

while water's ability to stick to other substances

水能够粘在别的物质上，

is called adhesion.

这叫做黏附性

Now, think back to the initial questions.

再回想最初的问题

First, why are some insects able to walk on water?

第一，为什么有些昆虫能够在水上爬行？

Surface tension due to hydrogen bonding

由于氢键，表面张力

creates a thin film on the surface of water

在水面上产生一层薄膜

that gives enough resistance

它的弹性足以支撑

for super-light insects to walk on.

小型昆虫在上面走动

You can't walk on it

而你不行

because the hydrogen bonds aren't strong enough

是因为氢键的强度不足以

to hold you up.

支撑你

Why does ice float on top of liquid water?

为什么冰能够漂浮在液态水中呢？

For most other substances,

对于大多数物质来说，

the solid state is more dense than the liquid state,

固态的密度总是比液态的密度大，

but that is not the case for water!

但是水却不是这样！

Hydrogen bonds keep water molecules

氢键在冻结的水中,水分子之间的

farther apart in frozen water than in liquid water.

距离比液态水更大

The farther apart the molecules are,

分子之间的距离越大，

the less dense that solid is.

固体的密度就越小

So ice is about 9% less dense than water,

所以冰的密度比水大约小9%，

which means it floats on the top.

所以它能漂浮在水上

That's why lakes freeze from the top down

这就是为什么湖水结冰时从水面开始往下结冰

and aquatic life is able to survive

所以水生生物能够度过

through a cold winter every year.

每年寒冷的冬天

It is the polarity of the water molecule

水分子的极性

and the resulting hydrogen bonding

和它造成的氢键

that account for water's unique properties.

构成了水独特的性质

So, the reason that water is so special,

水如此特殊的原因，

from inside your cells

从你身体中的细胞

to the world's oceans,

到地球上的海洋，

is simply because it is a polar molecule.

都是因为它是一个极性分子