首页
外语
计算机
考研
公务员
职业资格
财经
工程
司法
医学
专升本
自考
实用职业技能
登录
外语
One of the simplest and best known kinds of crystal is the ionic salt, of which a typical example is sodium chloride, or ordinar
One of the simplest and best known kinds of crystal is the ionic salt, of which a typical example is sodium chloride, or ordinar
admin
2015-01-31
27
问题
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 losing 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 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 framework 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.
In the first paragraph, the author is primarily concerned with______.
选项
A、introducing a variant on the standard atomic theory
B、describing how chlorine atoms can become negatively charged
C、providing background for the technical discussion to follow
D、describing some early research at Michigan State University
答案
C
解析
推断题。根据第1题的讨论结果,文章第二段开始一直关注的是新的科研发现——电子晶体,只有第一段的内容是普通的晶体,所以第一段内容是为引起下文而进行的学科普遍现象背景介绍.为后文进行铺垫。同时也和下文形成了对比。和选项C表述一致,所以C为正确答案。
转载请注明原文地址:https://kaotiyun.com/show/IFh7777K
0
大学英语六级
相关试题推荐
A、Thecandidatesintheelection.B、ThehistoryofAmerica.C、Socializedmedicine.D、Unemploymentinsurance.A
Mostpeopleareawarethatoutdoorairpollutioncandamagetheirhealth,butmanydonotknowthatindoorairpollutionalsoca
Researchershavefoundmoreevidencethatsuggestsarelationshipbetweenraceandratesoflungcanceramongsmokers.Some(36)
Choiceblindness:Youdon’tknowwhatyouwant[A]Wehaveallheardofexpertswhofailbasictestsofsensorydiscriminationin
Manyprivateinstitutionsofhighereducationaroundthecountryareindanger.Notallwillbesaved,andperhapsnotall【B1】__
Advertisementcanbethoughtof"asthemeansofmakingknowninordertobuyorsellgoodsorservices".Advertisementaimsto
A、AmericansarehappierthanEuropeans.B、TheGDPofEuropeishigherthanthatofAmerica.C、Peopleallovertheworldchooset
AccordingtothemostrecentAmericanFreshmansurvey,conductedannuallybytheUniversityofCalifornia,LosAngeles,undergra
NurseHomeVisits:ABoostforLow-IncomeParents[A]NursehomevisitorTammyBallardhashadsomememorableexperiencesinclos
TheEnglishnationalcharacterisdualistic:Oneaspectisconservative,theotherextroverted(性格外向的).Thepubisafineexample
随机试题
Itis______(legal)foraveragecitizensinChinatoownagun.
公民、法人或者其他组织向行政机关申请复议的,复议机关应当在收到申请书之日起多少天内作出决定(法律、法规另有规定的除外)
女,46岁。阴道出血20天入院。末次月经2002年9月20日。2002年10月18日,阴道淋漓出血,10天后血量增多有血块,伴下腹隐痛。既往月经6/30天,量中,无痛经。妊2产1,20年前顺产,此后人流一次。17年前带环至今。查体:血压120/80nunH
脉搏变化,不符合生理变化的是
背景资料:某承包商于某年承包某外资工程的施工,与业主签订的承包合同约定:工程合同价2000万元;若遇物价变动,工程价款采用调值公式动态结算;该工程的人工费占工程价款的35%,水泥占23%,钢材占12%,石料占8%,砂料占7%,不调值费用占15%;开工前业
从投资函数可知,影响投资变动的因素是()。
一张原始凭证上所列的支出需要由两个以上的单位共同负担时,应当由保存该原始凭证的单位将复制件提供给其他应负担单位。()
从法规类型(属性)上看,《学生伤害事故处理办法》属于()。
某保险公司近来的一项研究表明:那些在舒适工作环境里工作的人比在不舒适工作环境里工作的人的生产效率要高25%。这表明,日益改善的工作环境可以提高工人的生产率。以下哪个假设是对以上因果联系最严重的挑战?
某公司研发一种语音识别软件系统,需要对用户的语音指令进行音节分割、重音判断、语法分析和语义分析,最终对用户的意图进行推断。针对上述功能需求,该语音识别软件应该采用______架构风格最为合适。
最新回复
(
0
)