Resonance and Formal Charge · 共振与形式电荷
| English | 中文 | Pinyin · 拼音 |
|---|---|---|
| resonance/ˈrezənəns/ | 共振 | gòng zhèn |
| delocalized/dɪˈlɒkəlaɪzd/ | 离域 | lí yù |
| formal charge/ˈfɔːml tʃɑːdʒ/ | 形式电荷 | xíng shì diàn hè |
When one drawing isn't enough
- Some molecules refuse to fit a single Lewis picture.
- You can draw two or three that look equally right.
- The real molecule is a blend of them all.
- A quick bookkeeping trick tells you which drawing to trust.
当一幅图不够用时
- 有些分子拒绝套进单一的路易斯图。
- 你能画出两三幅看起来同样正确的图。
- 真实的分子是它们全部的混合。
- 一个快速的记账技巧告诉你该相信哪幅图。
Resonance: an average of structures
- Resonance 共振 means a molecule needs several Lewis structures.
- The true structure is an average, or hybrid, of them.
- The electrons are spread out, or delocalized 离域, across the molecule.
共振:多幅结构的平均
- 共振意味着一个分子需要好几幅路易斯结构。
- 真实结构是它们的平均(杂化体)。
- 电子在整个分子上散开,即离域。
A molecule with resonance is best described as... · 具有共振的分子最好描述为...
The real molecule is one steady average, not a flipping between forms. · 真实的分子是一个稳定的平均值，而不是在不同形态间翻转。
In a resonance hybrid, the electrons are spread out, or ____, over the molecule. · 在共振杂化体中，电子散布开来，或者说，在分子上是____的。
Resonance means the electrons are delocalized, not fixed to one bond. · 共振意味着电子是离域的，而不是固定在一个键上。
Formal charge
- Formal charge 形式电荷 checks how fairly electrons are shared:
- It compares an atom's electrons in the structure to its neutral count.
形式电荷
- 形式电荷检查电子分享得是否公平:
- 它把原子在结构中的电子数与它中性时的数目比较。
An oxygen atom (6 valence) has 4 lone electrons and 4 bonding electrons. Its formal charge? · 氧原子（6个价电子）有4个孤对电子和4个成键电子。它的形式电荷是多少？
$FC = 6 - 4 - \tfrac{1}{2}(4) = 6 - 4 - 2 = 0$.
Choosing the best structure
- The best Lewis structure keeps formal charges closest to zero.
- Any negative formal charge should sit on the most electronegative atom.
- The formal charges across the molecule must sum to its total charge.
选出最佳结构
- 最佳的路易斯结构使形式电荷尽量接近零。
- 任何负的形式电荷都应落在电负性最强的原子上。
- 整个分子的形式电荷之和必须等于它的总电荷。
The best Lewis structure has formal charges that are... · 最佳路易斯结构的形式电荷应该是...
Minimizing formal charge gives the most stable, most likely structure. · 最小化形式电荷给出最稳定、最可能的结构。
The formal charges of all atoms must add up to the molecule's overall charge. · 所有原子的形式电荷之和必须等于分子的总电荷。
For a neutral molecule they sum to zero; for an ion, to its charge. · 对于中性分子，总和为零；对于离子，为其所带电荷。
A negative formal charge is best placed on the... · 负的形式电荷最好放置在...
The most electronegative atom holds negative charge most comfortably. · 电负性最强的原子最能容纳负电荷。
Ozone $\text{O}_3$ has two resonance structures.
- In each one, one O--O bond is single and the other is double.
- The real molecule averages them: two equal bonds, each of order 1.5.
臭氧 $\text{O}_3$ 有两幅共振结构。
- 在每一幅中,一根 O--O 键是单键,另一根是双键。
- 真实分子把它们平均:两根相等的键,每根键级 1.5。
Assign the formal charges · 分配形式电荷
Formal charge = valence electrons - lone electrons - bonds. Assign each atom in the nitrate ion. · 形式电荷 = 价电子数 - 孤对电子数 - 键数。为硝酸根离子中的每个原子分配。
Resonance structures are not real states the molecule flips between -- it is one steady average of them, all the time. Formal charge is a bookkeeping tool, not a real charge on the atom. And the best structure minimizes formal charges and places any negative one on the most electronegative atom.
共振结构不是分子在它们之间来回切换的真实状态——它始终是它们的一个稳定平均。形式电荷是记账工具,不是原子上真实的电荷。而且最佳结构使形式电荷最小化,并把任何负电荷放在电负性最强的原子上。
Resonance means a molecule is the average of several Lewis structures, with electrons delocalized across it. Formal charge ($=$ valence $-$ lone $- \tfrac{1}{2}$ bonding electrons) is a bookkeeping check: the best structure keeps formal charges near zero, with any negative charge on the most electronegative atom.
共振意味着分子是几幅路易斯结构的平均,电子在其上离域。形式电荷($=$ 价电子 $-$ 孤对电子 $- \tfrac{1}{2}$ 成键电子)是记账检查:最佳结构让形式电荷接近零,任何负电荷落在电负性最强的原子上。