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
Learn about Noble Gases(惰性气体) Have you ever ridden on a balloon? Many tourist spots offer balloon rides in order for people
Learn about Noble Gases(惰性气体) Have you ever ridden on a balloon? Many tourist spots offer balloon rides in order for people
admin
2012-12-28
63
问题
Learn about Noble Gases(惰性气体)
Have you ever ridden on a balloon? Many tourist spots offer balloon rides in order for people to see the beauty of a place from above. A balloon contains a noble gas called helium(氦). Formerly, balloons contained hydrogen but hydrogen is very flammable and dangerous when uncontrolled. Therefore, people shifted to helium, which is safer. Helium is safe because it has the properties of the noble gases.
People once believed that noble gases couldn’t chemically react at all. For this reason, they were called inert gases(惰性气体). They were also listed under Group 0 in the old periodic table because scientists believed that the gases have zero valence(价)electrons in their outer shell. This was later proven to be untrue when some noble gas compounds were discovered.
The gases are elements, which share similar properties. These properties include being monoatomic, colorless, odorless, being able to conduct electricity, and having low chemical reactivity. Noble gases include Helium, Neon, Argon, Krypton, Xenon and Radoa These are all found in Group 18, in the rightmost column of the periodic table. If you look at the periodic table, you will notice that these elements are the only ones, which do not have a charge. Helium has the lowest molecular(分子的)weight while Radon is the heaviest.
Remember that chemical reactions occur because atoms have valence electrons, which are electrons in their outer shell. When the outer shell is "unfilled" or the required number of electrons is not yet complete, the atom is more reactive. Noble gases have a full outer shell, meaning that they have complete electrons in their outer shell. This complete number varies. For instance, the outer shell of Helium has 2 valence electrons while the outer shell of Xenon has 8 electrons. Nowadays, there remains to be a few noble gases because of the low chemical reactivity of these said gases.
Because of their properties, noble gases have many important applications. They are widely used in medicine and industries. For instance, liquid Helium is used for superconducting magnets(磁体). These magnets are very important in physics and medicine. When a doctor suspects that a person’s brain has been damaged, he might request for Magnetic Resonance Imaging(MRI). MRI allows the doctor to "see" the brain, without operating on the patient.
A. what is the periodic table?
B. What are noble gases?
C. What causes the low chemical reactivity of noble gases?
D. How were noble gases discovered?
E. How were noble gases understood in the past?
F. what are the applications of noble gases?
paragraph 2______.
选项
答案
E
解析
第二段首句的关键词once告知我们该段讲述的是“曾经”的事情。该段讲述的是人们过去对惰性气体的认识。故E(人们过去对惰性气体的理解)是正确选项。
转载请注明原文地址:https://kaotiyun.com/show/YlLd777K
本试题收录于:
职称英语理工类A级题库职称英语分类
0
职称英语理工类A级
职称英语
相关试题推荐
ThewriterbelievesthatthepopulationexplosionresultsfromAccordingtothepassage,whichofthefollowingstatementsabou
AnIntelligentCarDrivingneedssharpeyes,keenears,quickbrain,andcoordinationbetweenhandsandthebrain.Manyhumandr
AnIntelligentCarDrivingneedssharpeyes,keenears,quickbrain,andcoordinationbetweenhandsandthebrain.Manyhumandr
AnIntelligentCarDrivingneedssharpeyes,keenears,quickbrain,andcoordinationbetweenhandsandthebrain.Manyhumandr
AHarmScreeningMayDotoaYoungerWomanBInvestigatingtheEffectofScreeningCEffectsPredictedbyTwoDifferentMo
Sheshowslittleregardforthefeelingsofothersanddoesexactlywhatshewantsto.
YouNeedCourage!ShortlyafterIbeganacareerinbusiness,IlearnedthatCarlWeatherup,presidentofPepsiCo(百事可乐公司
FlyingtheHypertSkiesAlittleairplanehasgivennewmeaningtotheterm"goinghyper."TheHyper-Xrecentlybroket
MigrantWorkersInthepast20years,therehasbeenanincreasingtendencyforworkerstomovefromonecountrytoanother.
Frommystandpoint,thisthingisjustridiculous.
随机试题
A、剧烈头痛,呕吐B、膀胱刺激症状C、寒战、高热D、食欲锐减、恶心、呕吐E、心率增快,夜间不能平卧慢性肾炎并发尿毒症的早期表现()
Ⅲ期肿瘤药物临床试验病例选择要求
在工程质量保修期限内,因多方面原因造成的质量问题,要由()单位负责维修更换,由责任单位负责赔偿损失。
甲公司于20××年1月1日向银行借入一笔生产经营用短期借款,共计600000元,期限为9个月,年利率为5%。根据与银行签署的借款协议,该项借款的本金到期后一次归还;利息分月预提,按季支付。要求:编制甲公司1月末计提利息的会计分录;
八年级上册教材后设置了“课外古诗词背诵”部分,其中包括《长歌行》《野望》《早寒江上有怀》等共10首诗歌。从语文教材的构成要素来看,这属于语文教科书的()。
给定材料1.随着大众创业、万众创新时代的到来,中央配套了涉及大学毕业生、退伍军人、民间金融资本平台、惠农政策改革、创客空间、资本众筹、开放公共产品建设领域的一系列激励性强、创新意味浓厚、操作简便、惠利性好的政策措施,这些政策呼应大众创业、万众创新
甲公司于4月24日通知乙公司急需货物10吨,乙公司遂于4月25日按双方之间的交易惯例发货。4月26日甲公司义通知乙公司不需要该批货物。对此,下列说法正确的是()。(2017一专一32)
设f(x)连续,且f′(0)>0,则存在δ>0,使得().
Telecom:TheMergerIstheMessageLastyearendedwithabangintelecom.Duringthefinalthreemonths,Cingularclosedits
Directions:Forthispart,youareallowedthirtyminutestowriteashortessayentitledWhatIsthepurposeofpunishment.You
最新回复
(
0
)