范德华力简介
视频：
范德华力

分子间作用力，又称范德华力（van der Waals force），被描述为分子永久偶极和瞬间偶极引起的弱静电相互作用力。 分子间作用力（范德华力）有三个来源：①极性分子的永久偶极矩之间的相互作用。②一个极性分子使另一个分子极化，产生诱导偶极矩并相互吸引。③分子中电子的运动产生瞬时偶极矩，它使邻近分子瞬时极化，后者又反过来增强原来分子的瞬时偶极矩；这种相互耦合产生静电吸引作用，这三种力的贡献不同，通常第三种作用的贡献最大。

分子间作用力是只存在于分子(molecule)与分子之间或惰性气体(noble gas)原子(atom)间的作用力，又称范德华力(van der waals)，具有加和性，属于次级键。

氢键(hydrogen bond)、弱范德华力、疏水作用力、芳环堆积作用、卤键都属于次级键（又称分子间弱相互作用）。

In this video we'll discuss Van der Waals forces.
本视频将讨论范德华力·
Van der Waals forces are forces of attraction between molecules that are very close together.
范德华力是分子之间非常接近时产生的吸引力·
These forces between molecules are much weaker than the chemical bonds between the atoms holding a molecule together.
这些分子间的力比原子之间保持分子结合的化学键要弱得多·
Let's see how Van der Waals forces work.
让我们来看一下范德华力是如何作用的·
Molecules are electrically neutral because they have equal numbers of positively charged protons in the nucleus and negatively charged electrons outside the nucleus.
分子是电中性的,因为它们在原子核中有相等数量的正电荷质子和在原子核外的负电荷电子·
In addition some molecules are also polar.
此外,某些分子也是极性的·
What does this mean
这是什么意思呢?
Well polar molecules have permanent poles of electrical charge like a magnet because the electrons are unevenly distributed around the molecule.
极性分子像磁铁一样有永久的电荷极,因为电子在分子周围分布不均·
How does this happen
这是如何发生的呢?
Let's look at an example of a polar molecule water.
让我们看一个极性分子的例子——水·
A water molecule or H2O consists of two hydrogen atoms and one oxygen atom.
水分子,或称H2O,由两个氢原子和一个氧原子组成·
When a water molecule forms both hydrogen atoms bond with the oxygen atom by sharing their electrons with the oxygen atom.
当水分子形成时,两个氢原子通过与氧原子共享电子与氧原子结合·
This completes both oxygen's outer electron shell which can hold all eight electrons and hydrogen's outer shell which can hold two.
这使得氧的外层电子壳(最多能容纳八个电子)和氢的外层电子壳(最多容纳两个电子)都完成了填充·
However the electrons aren't shared equally between the atoms because the oxygen atom attracts the electrons more strongly than hydrogen.
然而,电子在原子之间的分配并不均匀,因为氧原子比氢原子更强烈地吸引电子·
As a result a partial negative charge develops around oxygen because there are more negatively charged electrons around the oxygen side of the molecule.
因此,氧周围会产生部分负电荷,因为氧分子一侧有更多带负电的电子·
In comparison fewer electrons around the hydrogen atoms create a partial positive charge on the hydrogen side of the molecule.
相比之下,氢原子周围的电子较少,这在分子中氢一侧产生了部分正电荷·
This unequal sharing of electrons creates opposing poles of electrical charge on either side of the two bonds that hold the atoms together.
这种电子共享不均衡在两个原子之间形成了电荷极性相反的电荷极·
Because of the opposite poles these bonds are called polar covalent bonds.
由于电荷极性相反,这些键被称为极性共价键·
And since a water molecule is angled or bent with both of the hydrogen atoms on one side
由于水分子呈角度或弯曲,两个氢原子位于一侧,
and the oxygen atom on the other side
氧原子位于另一侧,
the molecule as a whole also has opposite poles and therefore is referred to as a polar molecule.
因此整个分子也具有相反的电荷极性,因此被称为极性分子·
Now when polar molecules are near each other
现在,当极性分子彼此靠近时,
a Van der Waals force of attraction between the molecules occurs because of their oppositely charged poles.
由于它们的电荷极性相反,分子之间会产生范德华力吸引·
In this example
在这个例子中,
the attraction of a polar molecule's negative pole to the positive pole around hydrogen atoms in water is a particularly strong type of Van der Waals force called a hydrogen bond.
极性分子的负极与水中氢原子周围正极的吸引力是一种特别强的范德华力,称为氢键·
Hydrogen bonds only occur in polar molecules between hydrogen in one molecule and oxygen nitrogen and fluorine in the other.
氢键只在极性分子之间发生,涉及一个分子中的氢与另一个分子中的氧、氮和氟·
If a molecule doesn't have permanent poles of opposite electrical charge it's called a non polar molecule.
如果一个分子没有永久的电荷极性,它被称为非极性分子·
However non polar molecules can become polar for very brief moments since the locations of electrons around atoms are constantly changing.
然而,非极性分子可以在短暂的时刻变为极性分子,因为原子周围的电子位置不断变化·
This means the molecule can have a temporary negative pole on the side where there are momentarily more electrons
这意味着分子可以在一侧暂时有更多电子的地方形成负极,
and a temporary positive pole on the opposite side where there are fewer electrons.
而在电子较少的另一侧形成正极·
The momentary concentration of electrons in this molecule's negative pole can repel the electrons in a nearby molecule toward its opposite end making the neighboring molecule polar as well.
该分子负极电子的短暂浓度可以将附近分子的电子排斥到它的对面,使相邻分子也变成极性分子·
The oppositely charged poles of adjacent molecules attract each other forming weak connections between them called Van der Waals forces.
相邻分子相反电荷的极性会相互吸引,形成分子之间的弱连接,称为范德华力·
Van der Waals forces explains two important properties
范德华力解释了两个重要特性:
cohesion the attraction between like molecules within a substance
凝聚力——相似分子在物质内的吸引力,
and adhesion the attraction between unlike molecules in different substances.
以及附着力——不同物质中分子之间的吸引力·
An example of cohesion is when opposite poles of water molecules are attracted to each other but not to the surrounding air.
凝聚力的一个例子是,当水分子的相反电荷极吸引彼此时,但不会吸引周围的空气·
This creates an inward force allowing water to bead up and form water droplets.
这产生了一种向内的力,使水滴形成水珠·
Adhesion the force of attraction between unlike molecules explains how geckos are able to climb on slick flat surfaces.
附着力,即不同分子之间的吸引力,解释了壁虎如何能够在光滑的平面上爬行·
Although each molecular connection is very weak
尽管每个分子连接都非常微弱,
geckos can form millions of them between the molecules within the microscopic hairs on each foot and the molecules in the climbing surface.
但壁虎可以在每只脚上的微观毛发分子和攀爬表面的分子之间形成数百万个连接·
These connections add up to more than enough adhesion force to support the gecko's weight.
这些连接总和形成的附着力足以支持壁虎的重量·
In summary Van der Waals forces are forces of attraction between molecules.
总结一下,范德华力是分子之间的吸引力·
They are not the same as chemical bonds between atoms within a molecule.
它们不同于分子内部原子之间的化学键·
They can occur in permanently polar molecules such as water
它们可以发生在永久极性分子(如水)中,
and in non polar molecules when they become briefly polar due to the changing positions of electrons.
也可以发生在非极性分子中,当它们由于电子位置的变化而短暂变为极性分子时·
A hydrogen bond is a strong Van der Waals force between a polar molecule containing hydrogen atoms and the negative pole of another polar molecule.
氢键是一种强的范德华力,作用于一个包含氢原子的极性分子与另一个极性分子的负极之间·
Van der Waals forces account for cohesion
范德华力解释了凝聚力
the attraction between like molecules within a substance
相似分子在物质内部的吸引力,
and adhesion the attraction between unlike molecules in different substances.
以及附着力——不同物质之间分子间的吸引力·
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