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电极为什么会让水的特性改变 – 译学馆
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电极为什么会让水的特性改变

How polarity makes water behave strangely - Christina Kleinberg

为什么一些昆虫可以在
How come some insects are able to walk
池塘的表面驻足行走
on the surface of a pond,
而当你尝试在水面行走的时候
but you quickly sink to the bottom
你会非常快的就沉到了水底
when you try to walk on water?
为什么湖水在冬天结冰的时候是从上往下呢?
And why do lakes freeze from the top down in winter?
等等这类问题就要用极性这个属性去解释了
In a word, the answer to all these questions is polarity.
水分子的构成很简单
Water is a simple molecule
它是由一个氧原子和两个氢原子构成的
made up of one oxygen atom and two hydrogen atoms,
但却是生命不可或缺的物质
but it is essential to life.
事实上,水足足占了一个成年人
In fact, water makes up approximately 60%
百分之六十的体重
of the adult human being’s body weight.
正是水分子内的这种极性
The polarity within those water molecules
才使得这种普通的物质有了特性
gives this common substance the properties
并使之成为维持正常生命活动不可替代的物质
that make it unique and life-sustaining.
极性指的是在一个分子中
Polarity refers to the unequal sharing
电荷不均匀分布的这样一种特性
of electrons within a molecule.
对于水而言,这个氧原子和这两个氢原子之间有化学键
For water, the bonding between the oxygen atom
它在这一个水分子里
and two hydrogen atoms within a single water molecule
就相当于是两个人在拔河
is like a tug-of-war between a big, strong football player
一个是又高又壮的足球运动员,一个是正在学走路的小孩儿
and a cute little toddler.
氧原子是那个大的原子
Oxygen is a larger atom,
它在原子核中有比氢原子多的质子
with more protons in its nucleus than hydrogen.
这些带正电的质子所在就好比人的力气
These positive charges are like a person’s physical strength.
它们可以吸引
They’re able to attract
同结合成原子的带负电电子
the negatively charged electrons in the bond,
就像一个能强壮的人
just like a strong individual is able to overpower
可以在拔河中轻易拉赢一个缩小的人
a weaker individual in a tug of war.
所以,氧就可以吸引
So, oxygen is able to attract
比它本来应该有的还多的电子
more than its fair share of electrons.
因为氢比氧小,吸引电子的力量小,
Because hydrogen is smaller and has less strength,
或者说拥有的质子少
or fewer protons,
所以它在这场拔河中就输了
it loses the tug of war
能吸引到的电子数目比它应该有的还少
and attracts fewer than its fair share of electrons.
所以,在水中,氧就会呈现出负电
So, the oxygen in water behaves as though it’s negative,
氢就呈现出正电
and the hydrogens behave as though they’re positive.
这种结合方式在水分子中
The bonds within a single water molecule
就叫极性共价键
are called polar covalent bonds.
共价键意思就是电子在分子里是共用的
Covalent means that the electrons are shared.
但是,正如我们在前面学到的
But, as we just learned,
极性又意味着电子在分子中并不是公平地共用的
polar means that these electrons are not shared equally.
在水中,氧显负电性
In water, the oxygen acts negative
氢显正电性
and the hydrogens act positive.
由于正负相吸
Since negative and positive attract,
在相近的水分子中
that oxygen is attracted to the hydrogen atoms
氧就会被氢所吸引
in neighboring water molecules.
在水分子之间就会产生一种特殊形式的结合方式
A special type of bond forms between water molecules,
那就是氢键
known as a hydrogen bond.
氢键并不是只产生在水分子间
Hydrogen bonds don’t just happen in water either.
它也可以产生于水分子
They can form between a water molecule
和其他极性物质或者离子之间
and different substances that are polar or ionic.
水分子之间相互吸附的那种能力被称为结合力
Water’s ability to stick to itself is called cohesion,
然而水分子和其他物质的那种吸附能力
while water’s ability to stick to other substances
被称为附着力
is called adhesion.
现在,让我们回到原始的那个问题
Now, think back to the initial questions.
首先,为什么一些昆虫可以在水面上行走呢?
First, why are some insects able to walk on water?
表面张力的存在是因为
Surface tension due to hydrogen bonding
氢键在水的表面上创造了一层薄膜
creates a thin film on the surface of water
可以给那些特别轻的昆虫
that gives enough resistance
提供足够的支撑力
for super-light insects to walk on.
你不能在上面行走
You can’t walk on it
是因为氢键创造的薄膜不足以
because the hydrogen bonds aren’t strong enough
强大来支撑住你
to hold you up.
为什么水结冰是从上开始的呢?
Why does ice float on top of liquid water?
对于大多数其他物质
For most other substances,
固体的密度是大于液体的
the solid state is more dense than the liquid state,
但是水确不是这样的
but that is not the case for water!
氢键的存在使得在冰里面的
Hydrogen bonds keep water molecules
水分子的间距要大于液体水分子之间的间距
farther apart in frozen water than in liquid water.
分子的间距越大
The farther apart the molecules are,
固体的密度就越小
the less dense that solid is.
所以冰的密度比水还要小百分之九
So ice is about 9% less dense than water,
这就意味着冰应该浮在水面上
which means it floats on the top.
这就是为什么湖泊结冰都是从水面上开始
That’s why lakes freeze from the top down
使得水下生物得以生存
and aquatic life is able to survive
在每年的寒冷冬天里
through a cold winter every year.
正是存在于水分子中的极性
It is the polarity of the water molecule
和氢键的产生
and the resulting hydrogen bonding
才造就了水的这些独特属性
that account for water’s unique properties.
所以,为什么水对于
So, the reason that water is so special,
你身体里的细胞
from inside your cells
到地球上的海洋都是如此特别
to the world’s oceans,
就是因为它是个极性分子
is simply because it is a polar molecule.

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