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1、考研考博-考博英语-黑龙江大学模拟考试题含答案1. 不定项选择题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 l
2、osing one 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 changed). The ions are attracted to one another by their opposite charges, and they stack togeth
3、er 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 regularl
4、y 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 the
5、ir 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
6、 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
7、 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 framework of positive ions.By synthesizing elect
8、rides 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
9、 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 batt
10、eries. One obstacle is the tendency of electrides to decompose through reaction with air and water. Researchers are seeking ways to increase their stability.1. The passage is primarily concerned with discussing _.2. In the first paragraph, the author is primarily concerned with _.3. It can be inferr
11、ed from the passage that the differences between the behavior of anionic electrons and normal anions result from which of the following features of electrons, as compared to normal anions?I. The much lower mass of electrons.II. The much greater tendency of electrons to interact with one another over
12、 large distances.III. The much greater likelihood of electrons to remain trapped in naturally formed anionic cavities.4. According to the passage, the defining characteristic of an electride is which of the following?5. It can be inferred from the passage that anions behaving as “simple charged sphe
13、res” (3rd paragraph) could be expected to _.问题1选项A.a way to isolate electronsB.the characteristics of a new kind of crystalC.the structure of an ionic saltD.commercial uses for electridesE.the properties of ions问题2选项A.introducing a variant on the standard atomic theoryB.describing how chlorine atoms
14、 can become negatively chargedC.describing some early research at Michigan State UniversityD.presenting the identifying properties of an electrideE.providing background for the technical discussion to follow问题3选项A.I only.B.II only.C.I and II only.D.I and III only.E.II and III only.问题4选项A.Its positiv
15、e ions are of particularly low mass.B.Its ions possess identical electrical charges.C.It contains a framework of regularly stacked ions.D.Its ions demonstrate strong mutual attraction.E.Its negative ions consist solely of electrons.问题5选项A.readily lose electrons and become positively chargedB.move freely in and out of their cavitiesC.respond to photons by liberating electronsD.stack with other anions to create a regular frameworkE.remain fixed relative to their cations【答案】第1题:B第2题:E第3题:C第4题:E第5题:E【解析】1.【选项释义】The passage is primarily concerned with discussing_. 本文主要讨论_。A. a way to isol
