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范德華力簡(jiǎn)介

分子間作用力，又稱(chēng)范德華力（van der Waals force），被描述為分子永久偶極和瞬間偶極引起的弱靜電相互作用力。 分子間作用力（范德華力）有三個(gè)來(lái)源：①極性分子的永久偶極矩之間的相互作用。②一個(gè)極性分子使另一個(gè)分子極化，產(chǎn)生誘導(dǎo)偶極矩并相互吸引。③分子中電子的運(yùn)動(dòng)產(chǎn)生瞬時(shí)偶極矩，它使鄰近分子瞬時(shí)極化，后者又反過(guò)來(lái)增強(qiáng)原來(lái)分子的瞬時(shí)偶極矩；這種相互耦合產(chǎn)生靜電吸引作用，這三種力的貢獻(xiàn)不同，通常第三種作用的貢獻(xiàn)最大。

分子間作用力是只存在于分子(molecule)與分子之間或惰性氣體(noble gas)原子(atom)間的作用力，又稱(chēng)范德華力(van der waals)，具有加和性，屬于次級(jí)鍵。

氫鍵(hydrogen bond)、弱范德華力、疏水作用力、芳環(huán)堆積作用、鹵鍵都屬于次級(jí)鍵（又稱(chēng)分子間弱相互作用）。

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In this video we'll discuss Van der Waals forces
本視頻將討論范德華力·
Van der Waals forces are forces of attraction between molecules that are very close together
范德華力是分子之間非常接近時(shí)產(chǎn)生的吸引力·
These forces between molecules are much weaker than the chemical bonds between the atoms holding a molecule together
這些分子間的力比原子之間保持分子結(jié)合的化學(xué)鍵要弱得多·
Let's see how Van der Waals forces work
讓我們來(lái)看一下范德華力是如何作用的·
Molecules are electrically neutral because they have equal numbers of positively charged protons in the nucleus and negatively charged electrons outside the nucleus
分子是電中性的,因?yàn)樗鼈冊(cè)谠雍酥杏邢嗟葦?shù)量的正電荷質(zhì)子和在原子核外的負(fù)電荷電子·
In addition some molecules are also polar
此外,某些分子也是極性的·
What does this mean
這是什么意思呢?
Well polar molecules have permanent poles of electrical charge like a magnet because the electrons are unevenly distributed around the molecule
極性分子像磁鐵一樣有永久的電荷極,因?yàn)殡娮釉诜肿又車(chē)植疾痪?/div>
How does this happen
這是如何發(fā)生的呢?
Let's look at an example of a polar molecule water
讓我們看一個(gè)極性分子的例子——水·
A water molecule or H2O consists of two hydrogen atoms and one oxygen atom
水分子,或稱(chēng)H2O,由兩個(gè)氫原子和一個(gè)氧原子組成·
When a water molecule forms both hydrogen atoms bond with the oxygen atom by sharing their electrons with the oxygen atom
當(dāng)水分子形成時(shí),兩個(gè)氫原子通過(guò)與氧原子共享電子與氧原子結(jié)合·
This completes both oxygen's outer electron shell which can hold all eight electrons and hydrogen's outer shell which can hold two
這使得氧的外層電子殼(最多能容納八個(gè)電子)和氫的外層電子殼(最多容納兩個(gè)電子)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,電子在原子之間的分配并不均勻,因?yàn)檠踉颖葰湓痈鼜?qiáng)烈地吸引電子·
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?chē)鷷?huì)產(chǎn)生部分負(fù)電荷,因?yàn)檠醴肿右粋?cè)有更多帶負(fù)電的電子·
In comparison fewer electrons around the hydrogen atoms create a partial positive charge on the hydrogen side of the molecule
相比之下,氫原子周?chē)碾娮虞^少,這在分子中氫一側(cè)產(chǎn)生了部分正電荷·
This unequal sharing of electrons creates opposing poles of electrical charge on either side of the two bonds that hold the atoms together
這種電子共享不均衡在兩個(gè)原子之間形成了電荷極性相反的電荷極·
Because of the opposite poles these bonds are called polar covalent bonds
由于電荷極性相反,這些鍵被稱(chēng)為極性共價(jià)鍵·
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彎曲,兩個(gè)氫原子位于一側(cè),
and the oxygen atom on the other side
氧原子位于另一側(cè),
the molecule as a whole also has opposite poles and therefore is referred to as a polar molecule
因此整個(gè)分子也具有相反的電荷極性,因此被稱(chēng)為極性分子·
Now when polar molecules are near each other
現(xiàn)在,當(dāng)極性分子彼此靠近時(shí),
a Van der Waals force of attraction between the molecules occurs because of their oppositely charged poles
由于它們的電荷極性相反,分子之間會(huì)產(chǎn)生范德華力吸引·
In this example
在這個(gè)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
極性分子的負(fù)極與水中氫原子周?chē)龢O的吸引力是一種特別強(qiáng)的范德華力,稱(chēng)為氫鍵·
Hydrogen bonds only occur in polar molecules between hydrogen in one molecule and oxygen nitrogen and fluorine in the other
氫鍵只在極性分子之間發(fā)生,涉及一個(gè)分子中的氫與另一個(gè)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
如果一個(gè)分子沒(méi)有永久的電荷極性,它被稱(chēng)為非極性分子·
However non polar molecules can become polar for very brief moments since the locations of electrons around atoms are constantly changing
然而,非極性分子可以在短暫的時(shí)刻變?yōu)闃O性分子,因?yàn)樵又車(chē)碾娮游恢貌粩嘧兓?/div>
This means the molecule can have a temporary negative pole on the side where there are momentarily more electrons
這意味著分子可以在一側(cè)暫時(shí)有更多電子的地方形成負(fù)極,
and a temporary positive pole on the opposite side where there are fewer electrons
而在電子較少的另一側(cè)形成正極·
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
該分子負(fù)極電子的短暫濃度可以將附近分子的電子排斥到它的對(duì)面,使相鄰分子也變成極性分子·
The oppositely charged poles of adjacent molecules attract each other forming weak connections between them called Van der Waals forces
相鄰分子相反電荷的極性會(huì)相互吸引,形成分子之間的弱連接,稱(chēng)為范德華力·
Van der Waals forces explains two important properties
范德華力解釋了兩個(gè)重要特性:
cohesion the attraction between like molecules within a substance
凝聚力——相似分子在物質(zhì)內(nèi)的吸引力,
and adhesion the attraction between unlike molecules in different substances
以及附著力——不同物質(zhì)中分子之間的吸引力·
An example of cohesion is when opposite poles of water molecules are attracted to each other but not to the surrounding air
凝聚力的一個(gè)例子是,當(dāng)水分子的相反電荷極吸引彼此時(shí),但不會(huì)吸引周?chē)目諝狻?/div>
This creates an inward force allowing water to bead up and form water droplets
這產(chǎn)生了一種向內(nèi)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
附著力,即不同分子之間的吸引力,解釋了壁虎如何能夠在光滑的平面上爬行·
Although each molecular connection is very weak
盡管每個(gè)分子連接都非常微弱,
geckos can form millions of them between the molecules within the microscopic hairs on each foot and the molecules in the climbing surface
但壁虎可以在每只腳上的微觀毛發(fā)分子和攀爬表面的分子之間形成數(shù)百萬(wàn)個(gè)連接·
These connections add up to more than enough adhesion force to support the gecko's weight
這些連接總和形成的附著力足以支持壁虎的重量·
In summary Van der Waals forces are forces of attraction between molecules
總結(jié)一下,范德華力是分子之間的吸引力·
They are not the same as chemical bonds between atoms within a molecule
它們不同于分子內(nèi)部原子之間的化學(xué)鍵·
They can occur in permanently polar molecules such as water
它們可以發(fā)生在永久極性分子(如水)中,
and in non polar molecules when they become briefly polar due to the changing positions of electrons
也可以發(fā)生在非極性分子中,當(dāng)它們由于電子位置的變化而短暫變?yōu)闃O性分子時(shí)·
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
氫鍵是一種強(qiáng)的范德華力,作用于一個(gè)包含氫原子的極性分子與另一個(gè)極性分子的負(fù)極之間·
Van der Waals forces account for cohesion
范德華力解釋了凝聚力
the attraction between like molecules within a substance
相似分子在物質(zhì)內(nèi)部的吸引力,
and adhesion the attraction between unlike molecules in different substances
以及附著力——不同物質(zhì)之間分子間的吸引力·