阅读36套一道题，大家帮忙看一下，多谢啦！

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全文：
In electrides, the anions (negative ions) are completely replaced by electrons, which are trapped in naturally formed cavities within a framework of regularly stacked cations (positive ions). Unlike other types of anions, anionic electrons do not behave as if they were simple charged spheres. The properties of an electride depend largely on the distance between the cavities that hold trapped electrons. When the trapped electrons are far apart, they do not interact strongly, and so behave somewhat like an array of isolated negative charges. When they are closer together, they begin to display properties associated with large ensembles of identical particles. When they are still closer, the ensemble properties dominate and the electrons "delocalize".


It can be inferred from the passage that an electride behaves most like a normal ionic crystal when the electride has which of the following features?
(A) The anionic cavities are widely separated.
(B) All of the trapped electrons are able to delocalize.
(C) The trapped electrons are liberated by impinging photons.
(D) The ions are tightly packed together.
(E) Most of the cations have lost their electrical charge.

这道题答案是A，不知道是怎么推出来的，求指点~~谢谢了

辰南UID: 3613235

注意这一句  when the trapped xxxx.they do not interact strongly  xxx  后面又说到了 close时的影响。所以距离较远 就不容易相互影响  所以就是normal啦

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辰南 发表于 2015-9-9 14:54
注意这一句  when the trapped xxxx.they do not interact strongly  xxx  后面又说到了 close时的影响。所 ...

但是文中好像没有说normal ionic crystal 不会相互影响吧，难道an array of isolated negative charges 就是normal ionic crystal吗？？ 多谢了

辰南UID: 3613235

。。文中已经说了越接近 相互作用就越强啊  就会朝着delocalize的方向发展。。相比较于这种趋势。个人觉得初始状态就是normal  而且其他选项在文中也找不到对应啊

asceticabardUID: 3338402

从第一句话可以看出electrides 是取代negative ions来的，填充到阳离子的空隙中，原始的模型包含正负离子就是离子晶体啦。第二句话说但又不只是表现simple charged spheres。结合后面的介绍，所以选A。
我也做错了。。。
虽然我学了化学
当时没有想到化学知识，只是根据文章来做题，如果只看题目不看文章我应该可以做对。。。
后面的delocalize是离域，这是共价键的性质了
感觉这题专业性要求比较高。。。

或者按楼上的方法也可以，只有第一种情况有“like”类比

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asceticabard 发表于 2015-9-11 20:37
从第一句话可以看出electrides 是取代negative ions来的，填充到阳离子的空隙中，原始的模型包含正负离子就 ...

我也是学化学的，还学了一些晶体学。。。所以这句话 “When the trapped electrons are far apart, they do not interact strongly, and so behave somewhat like an array of isolated negative charges.” 最后半句说像一排孤立负电荷的行为，做题时想正常离子晶体里负电荷并不是孤立的，所以就没把这个当作是normal ionic crystal

不过这道题也只能选A了，多谢了！

岳然UID: 3654715

又是拿老题改编随意删减原文酿成的惨剧，原文在此：

One of the simplest and best known kinds of crystal is the ionic salt, of which a typical example is sodium chloride, or ordinary table salt. The fundamental components of an ionic salt are ions: atoms or molecules that have become electrically charged by gaining or losing one or more electrons. In forming sodium chloride, for example, sodium atoms give up an electron (thereby becoming, positively charged) and chlorine atoms gain an electron (thereby becoming negatively   charged). The ions are attracted to one another by their opposite charges, and they stack together compactly, like tightly packed spheres.    

Recently, scientists at Michigan State University created a new kind of crystal called an electride. In electrides, the anions (negative ions) are completely replaced by electrons,    which are trapped in naturally formed cavities within a framework of regularly stacked cations (positive ions). Electrides are the first examples of ionic salts in which all these anionic sites are occupied solely by electrons. Unlike other types of anions, anionic electrons do not behave as if they were simple charged spheres. In particular, because of their low mass and their tendency to interact with one another over great distances, they cannot be "pinned down" to any one location. Instead, they wander close to and among the atoms lining the cavity and interact with electrons in nearby cavities, perhaps changing places with them.     

The properties of an electride depend largely on the distance between the cavities that hold trapped electrons. When the trapped electrons are far apart, they do not interact strongly,   and so behave somewhat like an array of isolated negative charges. When they are closer together, they begin to display properties associated with large ensembles of identical particles. When they are still closer, the ensemble properties dominate and the electrons   "delocalize":they are no longer tightly bound within individual cavities but are more or less free to pass through the spaces within the frame-work of positive ions.     

By synthesizing electrides from a variety of materials, one can vary the geometry of the anionic cavities and their relation to the surrounding cations. The resulting properties may   make it possible for electrides to become a basis for economically useful new materials and devices. For instance, because the electrons in some electrides are very weakly bound, these crystals could be effective as photosensitive detectors, in which an impinging photon liberates an electron, resulting in a small electric current. The same weak binding could also make electrides useful in solar-energy converters and as cathodes in batteries. One obstacle is the tendency of electrides to decompose through reaction with air and water. Researchers are seeking ways to increase their stability.


已知 normal ionic salt -> like tightly packed spheres
且 electride中的electron -> do not behave as if they were simple charged spheres 因为 their tendency to interact with one another
而当electrons are far apart 时 -> they do not interact strongly
所以选A

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岳然 发表于 2015-9-17 20:33
又是拿老题改编随意删减原文酿成的惨剧，原文在此：

One of the simplest and best known kinds of crys ...

哇多谢了！normal ionic crystal 中的tightly packed spheres 是由一正一负离子结合在一起组成的，这个整体是isolated, 而在electride中的electron当距离远时是isolated 不会相互作用， 相当于把正常晶体中的正负离子结合体与electride中的电子类比，是这个意思吧?

asceticabardUID: 3338402

WWOW 发表于 2015-9-17 20:10
我也是学化学的，还学了一些晶体学。。。所以这句话 “When the trapped electrons are far apart, they  ...

我也是想离子晶体并不是孤立的，但正负离子相距很远（相对于离子半径来说）吧，可以大致看成孤立的？

岳然UID: 3654715

WWOW 发表于 2015-9-17 21:04
哇多谢了！normal ionic crystal 中的tightly packed spheres 是由一正一负离子结合在一起组成的，这个整 ...

我觉得你背景知识太多导致把这个问题复杂化了。从文章来看，electride和ionic crystal的区别就是electride中的anionic electrons之间会互相作用，而一般的ionic crystal中的anion不会互相作用，所以当electride中那些electron隔得足够远而没有相互作用以后，它就变成了一般的ionic crystal

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岳然 发表于 2015-9-17 21:20
我觉得你背景知识太多导致把这个问题复杂化了。从文章来看，electride和ionic crystal的区别就是electrid ...

明白了 太感谢了:）

岳然UID: 3654715

WWOW 发表于 2015-9-17 21:32
明白了 太感谢了:）

不客气 :D

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asceticabard 发表于 2015-9-17 21:18
我也是想离子晶体并不是孤立的，但正负离子相距很远（相对于离子半径来说）吧，可以大致看成孤立的？

根据原文第一段末尾来看应该是tightly packed spheres是孤立的，由一正一负离子组成~