英語短文練習(xí)(文檔良心出品)

短文一Theatomisabasicunitofmatterthatconsistsofadensecentralnucleussurroundedbyacloudofnegativelychargedelectrons.Theatomicnucleuscontainsamixofpositivelychargedprotonsandelectricallyneutralneutrons.Theelectronsofanatomareboundtothenucleusbytheelectromagneticforce.Anatomcontaininganequalnumberofprotonsandelectronsiselectricallyneutral,otherwiseitispositivelyornegativelychargedandisknownasanion.Anatomisclassifiedaccordingtothenumberofprotonsandneutronsinitsnucleus:thenumberofprotonsdeterminesthechemicalelement,andthenumberofneutronsdeterminestheisotopeoftheelement.原子是物質(zhì)的基本單位，由密集的中央核周圍有云帶負(fù)電荷的電子。原子核包含一個組合的帶正電的質(zhì)子和電中性的中子。一個原子的電子被電磁力約束的核。原子含有相同數(shù)目的質(zhì)子和電子是電中性的，否則它是正或負(fù)電荷，稱為離子。根據(jù)其原子核的質(zhì)子和中子的數(shù)量分類：質(zhì)子數(shù)決定元素，而中子數(shù)決定元素的同位素。短文二Analyticalchemistryisthestudyoftheseparation,identification,andquantificationofthechemicalcomponentsofnaturalandartificialmaterials.Analyticalmethodscanbeseparatedintoclassicalandinstrumental.Classicalmethodsuseseparationssuchasprecipitation,extraction,anddistillationandqualitativeanalysisbycolor,odor,ormeltingpoint.Quantitativeanalysisisachievedbymeasurementofweightorvolume.Instrumentalmethodsuseanapparatustomeasurephysicalquantitiesoftheanalytesuchaslightabsorption,fluorescence,orconductivity.Theseparationofmaterialsisaccomplishedusingchromatography,electrophoresis.分析化學(xué)是研究的分離，鑒定，以及自然和人工材料的化學(xué)成分定量分析。分析方法可分為經(jīng)典和儀器。傳統(tǒng)的方法使用的分離，如沉淀，萃取，蒸餾和定性分析的顏色，氣味，或熔點(diǎn)。定量分析是以重量或體積測量的實(shí)現(xiàn)。儀器方法使用一個測量裝置的被分析物，如光吸收，熒光的物理量，或電導(dǎo)率。材料的分離是通過使用色譜法，電泳。短文三Chromatographyisaseparationandanalysistechnique.Themixtureisdissolvedinafluidcalledthemobilephase,whichcarriesitthroughanothermaterialcalledthestationaryphase.Thevariousconstituentsofthemixturetravelatdifferentspeeds,causingthemtoseparate.Theseparationisbasedondifferentialpartitioningbetweenthemobileandstationaryphases.Subtledifferencesinacompound'spartitioncoefficientresultindifferentialretentiononthestationaryphase.Chromatographymaybepreparativeoranalytical.Thepurposeofpreparativechromatographyistoseparatethecomponentsandfurthergetpurifiedcomponents.Analyticalchromatographyisdonenormallywithsmalleramountsofmaterialandisformeasuringtherelativeproportionsofanalytesinamixture.色譜是一種分離和分析技術(shù)?；旌衔锶芙庥诹黧w稱為流動相，進(jìn)行通過另一種物質(zhì)稱為固定相。在不同速度下的混合各種成分的旅行，使他們分開。分離是基于差分移動和固定相之間的分配。在固定相的化合物的分配系數(shù)產(chǎn)生微分保持微妙的差異。色譜法可制備或分析。制備色譜的目的是分離的組件，進(jìn)一步得到純化的成分。解析法是通常與少量的物質(zhì)是混合物中測量分析物的相對比例。短文四Abufferisanaqueoussolutionconsistingofamixtureofaweakacidanditsconjugatebaseoraweakbaseanditsconjugateacid.ItspHchangesverylittlewhenasmallamountofstrongacidorbaseisaddedtoitandthusitisusedtopreventchangesinthepHofasolution.BuffersolutionsareusedasameansofkeepingpHatanearlyconstantvalueinawidevarietyofchemicalapplications.ManylifeformsthriveonlyinarelativelysmallpHrangesotheyutilizeabuffersolutiontomaintainaconstantpH.Oneexampleofabuffersolutionfoundinnatureisblood.緩沖溶液由弱酸及其共軛堿或弱堿及其共軛酸的混合物。pH值的變化非常小，當(dāng)少量的強(qiáng)酸或堿加入它，因此它是用來防止在溶液pH的變化。緩沖溶液作為pH值保持在多種化學(xué)應(yīng)用的一個幾乎恒定的值的方式。許多形式的生命茁壯成長，只在一個相對較小的pH值范圍內(nèi)，所以他們利用保持恒定的pH緩沖溶液的一個例子在自然界中發(fā)現(xiàn)的緩沖溶液是血。短文五Amoleculeisanelectricallyneutralgroupoftwoormoreatomsheldtogetherbycovalentchemicalbonds.Moleculesaredistinguishedfromionsbytheirlackofelectricalcharge.Amoleculeofasubstancecannotbeseenbythenakedeye-adropofwaterismadeupofmany,manymoleculesofwater.Scientistsbelievethatmoleculesarealwaysmoving.Theycanbesolids,liquidsorgases.Moleculesmovethemostandarethefurthestapartwhentheyaregases.Moleculesareclosesttogetherandmovethemostslowlywhentheyaresolids.Moleculesthatareliquidsmovementisbetweenthoseofgasesandthoseofsolids.Moleculescomeindifferentsizesandmolecularweights.Theiratomscanbearrangedindifferentways.Moleculesinsubstancescanbesplitupinchemicalreactionstoformothermolecules.Theycanalsorecombineintolargermoleculesorbebrokendownintosmallermolecules.一個分子是由化學(xué)鍵結(jié)合在一起的兩個或兩個以上的原子的電中性的組。分子與離子的電荷的缺乏。一種物質(zhì)不能分子被肉眼看到一滴水是由許多，許多水分子。

科學(xué)家認(rèn)為，分子總是在不斷地運(yùn)動。他們可以是固體，液體或氣體。分子移動最是最遠(yuǎn)時，氣體。分子是最接近的移動最慢時，固體的。分子，液體運(yùn)動的氣體和固體之間的。

分子有不同的大小和分子量。他們的原子可以在不同的排列方式。分子物質(zhì)可分成化學(xué)反應(yīng)形成其他分子。他們還可以組合成更大的分子或被分解成更小的分子。短文六Liquidisoneofthefourfundamentalstatesofmatter(theothersbeingsolid,gas,andplasma),andistheonlystatewithadefinitevolumebutnofixedshape.Aliquidismadeupoftinyvibratingparticlesofmatter,suchasatomsandmolecules,heldtogetherbyintramolecularbonds.Wateris,byfar,themostcommonliquidonEarth.Likeagas,aliquidisabletoflowandtaketheshapeofacontainer.Someliquidsresistcompression,whileotherscanbecompressed.Unlikeagas,aliquiddoesnotdispersetofilleveryspaceofacontainer,andmaintainsafairlyconstantdensity.Adistinctivepropertyoftheliquidstateissurfacetension,leadingtowettingphenomena.Thedensityofaliquidisusuallyclosetothatofasolid,andmuchhigherthaninagas.Therefore,liquidandsolidarebothtermedcondensedmatter.Ontheotherhand,asliquidsandgasessharetheabilitytoflow,theyarebothcalledfluids.AlthoughliquidwaterisabundantonEarth,thisstateofmatterisactuallytheleastcommonintheknownuniverse,becauseliquidsrequirearelativelynarrowtemperature/pressurerangetoexist.液體是物質(zhì)的四種基本狀態(tài)（其它是固體，氣體，等離子體）