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化學鍵介紹
離子鍵與共價鍵

化學鍵（chemical bond）是純凈物分子內或晶體內相鄰兩個或多個原子（或離子）間強烈的相互作用力的統稱。使離子相結合或原子相結合的作用力通稱為化學鍵。
離子鍵、共價鍵、金屬鍵各自有不同的成因，離子鍵是通過原子間電子轉移，形成正負離子，由靜電作用形成的。共價鍵的成因較為復雜，路易斯理論認為，共價鍵是通過原子間共用一對或多對電子形成的，其他的解釋還有價鍵理論，價層電子互斥理論，分子軌道理論和雜化軌道理論等。金屬鍵是一種改性的共價鍵，它是由多個原子共用一些自由流動的電子形成的。

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視頻
教程課件
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In this video we will compare ionic and covalent bonds
本視頻將對比離子鍵和共價鍵·
In order to understand ionic bonds we need to talk about ions first
為了理解離子鍵,我們首先需要討論離子·
Atoms are electrically neutral because they have equal numbers of both positively charged protons and negatively charged electrons
原子是電中性的,因為它們擁有相等數量的正電荷質子和負電荷電子·
However an atom can become a charged particle called an ion if it gains or loses electrons
然而,如果一個原子獲得或失去電子,它可以變成帶電粒子,稱為離子·
If an atom gains electrons it acquires more negative charge
如果一個原子獲得電子,它會得到更多的負電荷·
As a result it becomes a negatively charged ion
因此,它會變成帶負電的離子·
Conversely if an atom loses electrons it loses some of its negative charge and becomes a positively charged ion
相反,如果一個原子失去電子,它失去了一部分負電荷,變成帶正電的離子·
The only way to get a positively charged ion is to lose negatively charged electrons
獲得帶正電的離子唯一的方法是失去帶負電的電子·
Remember you can't just add a proton to make a positive ion because changing the number of protons would change it into a different element
記住,不能僅僅添加一個質子來制造正離子,因為改變質子數量會使它變成不同的元素·
Now let's talk about ionic bonds
現在,我們來談談離子鍵·
Notice that this term contains the word ion
注意,這個術語包含了"離子"一詞·
That's because ionic bonds create ions out of electrically neutral atoms by the transfer of one or more valence electrons from one atom to another
這是因為離子鍵通過從一個原子向另一個原子轉移一個或多個價電子,將電中性的原子轉化為離子·
Further electrically neutral atoms of elements whose outer shell is less than half filled with valence electrons tend to donate electrons
此外,外層電子不足半滿的元素原子傾向于捐贈電子,
while atoms whose outer shell is more than half filled tend to attract electrons
而外層電子超過半滿的原子則傾向于吸引電子·
For example sodium and chlorine atoms are electrically neutral
例如,鈉和氯原子是電中性的·
Chlorine which only needs one electron to fill its outer shell strongly attracts sodium's single valence electron
氯只需要一個電子來填滿外層電子,因此它強烈吸引鈉的單個價電子·
So these elements react to form a chemical bond creating sodium chloride
因此,這些元素發生反應,形成化學鍵,生成氯化鈉·
Sodium chloride otherwise known as table salt is an example of an ionically bonded compound
氯化鈉,也就是常見的食鹽,是一個離子鍵結合的化合物示例·
This is because the electrically neutral sodium atom became a positively charged ion by losing its valence electron
這是因為電中性的鈉原子通過失去其價電子變成了帶正電的離子·
And chlorine became a negatively charged ion by gaining this electron from sodium
氯通過從鈉獲得電子,變成了帶負電的離子·
So how do covalent bonds occur
那么,共價鍵是如何形成的呢?
The simplest substance that contains a covalent bond is a molecule of hydrogen gas also known as H2
含有共價鍵的最簡單物質是氫氣分子,也叫做H2·
A hydrogen atom has only one electron in its outer shell which for this atom is also the shell nearest the nucleus
一個氫原子只有一個電子在它的外層電子殼,這個殼層也是最靠近原子核的殼層·
This shell can hold a maximum of two electrons
這個殼層最多可以容納兩個電子·
So atoms of hydrogen tend to pair up and share their electrons so that both atoms have their outer shell filled
因此,氫原子傾向于配對并共享電子,以使兩個原子的外層電子殼都得到填充·
As you can see covalent bonds occur when atoms share pairs of electrons
如你所見,共價鍵在原子共享一對電子時形成·
In this molecule the hydrogen atoms form a single covalent bond
在這個分子中,氫原子形成了一個單一的共價鍵·
Another example of a covalently bonded molecule is carbon dioxide or CO2
另一個共價鍵結合的分子示例是二氧化碳,或CO2·
From its chemical formula you know that carbon dioxide contains one carbon atom and two oxygen atoms
從其化學式中,你可以知道二氧化碳包含一個碳原子和兩個氧原子·
Carbon has four valence electrons
碳有四個價電子,
and both oxygen atoms have six valence electrons
而兩個氧原子都有六個價電子·
But all three atoms would need eight electrons to fill their outer shells
但是,所有三個原子都需要八個電子才能填滿它們的外層電子殼·
So each oxygen atom shares a pair of electrons with the pair of electrons in carbon
因此,每個氧原子與碳的電子對共享一對電子·
This results in two double covalent bonds where two pairs of electrons are shared between each atom
這導致了兩個雙重共價鍵,其中每個原子之間共享兩對電子·
To summarize the two main types of chemical bonds are ionic bonds and covalent bonds
總結一下,化學鍵有兩種主要類型,分別是離子鍵和共價鍵·
In ionic bonds one or more electrons are transferred from one atom to another
在離子鍵中,一個或多個電子從一個原子轉移到另一個原子·
In covalent bonds one or more pairs of electrons are shared between atoms
在共價鍵中,一個或多個電子對在原子之間共享·