托福阅读素材：元素周期表的发展

智课网 TOEFL备考资料 托福阅读素材：元素周期表的发展 摘要： 托福阅读素材：元素周期表的发展，下面是小马过河为同学们搜集整理的托福阅读素材的相 关信息，小马小编整理过来，供同学们参考。 托福 化学类阅读文章翻译，Development of the PeriodicTable元素周期表的发展 文章词汇words 元素element 族 group 原子序数atomic number 同位素isotope 化学性质chemical property 物理性质physical property 原子atom 原子核nucleus 质子proton 中子neutron 电子electron 稀有气体rare gases 碱金属alkali metal 文章翻译translation 一、元素周期表出现的背景 The periodic table is a chart that reflects the periodic recurrence of chemical and physicalproperties of the elements when the elements are arranged in order of increasing atomicnumber (the number of protons in the nucleus). It is a monumental scientific achievement,and its development illustrates the essential interplay between observation, prediction, andtesting required for scientific progress. In the 1800s scientists were searching for newelements. By the late 1860s more than 60 chemical elements had been identified, and muchwas known about their descriptive chemistry. Various proposals were put forth to arrange theelements into groups based on similarities in chemical and physical properties. The next stepwas to recognize a connection between group properties (physical or chemical similarities) andatomic mass (the measured mass of an individual atom of an element). When the elementsknown at the time were ordered by increasing atomic mass, it was found that successiveelements belonged to different chemical groups and that the order of the groups in thissequence was fixed and repeated itself at regular intervals. It was a natural Idea to break upthe series of elements at the points where the sequence of chemical groups to which theelements belonged began to repeat itself. Thus when the series of elements was written so asto begin a new horizontal row with each alkali metal, elements of the same groups wereautomatically assembled in vertical columns in a periodic table of the elements. This tablewas the forerunner of the modern table. 元素周期表是一个按照原子序数(原子核中的质子数)排列的反映元素化学和物理性质周期性再 现的一个图表。它是一个里程碑式的科学成就，它的发展阐明了科学发展中的观察、预测、 测试之间的必要关系。19世纪的科学家都在找寻新的元素。到了19世纪60年代晚期，有60多 种元素被发现，人们对于他们的化学性质也多有了解。基于这些元素的化学性质和物理性质 的相似性，人们提出各种方案来对这些元素进行分类。然后就是找到群族的元素性质(物理或 化学性质的相似性)和原子质量( 测量的单个元素的原子质量) 之间的联系。当人们按照不断增 加的原子质量的顺序排列这些已知的元素时，发现连续的元素属于不同的化学群族，群族的 顺序在这一序列中是固定的，并按照一定的间隔重复。很自然人们想到在这些元素所在群族 的序列开始自我重复的哪一点上分开这一系列的元素。因此，当这一系列的元素以碱金属开 始一段水平的一行，同族的元素被自动聚集到元素周期表的垂直的一列当中。这个图表是现 在元素周期表的前身。 二、元素周期表和原子质量的关系 When the German chemist Lothar Meyer and (independently) the Russian Dmitry Mendeleyevfirst introduced the periodic table in 1869-70, one-third of the naturally occurring chemicalelements had not yet been discovered. Yet both chemists were sufficiently farsighted to leavegaps where their analyses of periodic physical and chemical properties indicated that newelements should be located. Mendeleyev was bolder than Meyer and even assumed that if ameasured atomic mass put an element in the wrong place in the table, the atomic mass waswrong. In some cases this was true. Indium, for example, had previously been assigned anatomic mass between those of arsenic and selenium. Because there is no space in the periodictable between these two elements, Mendeleyev suggested that the atomic mass of indium bechanged to a completely different value, where it would fill an empty space between cadmiumand tin. In fact, subsequent work has shown that in a periodic table, elements should not beordered strictly by atomic mass. For example, tellurium comes before iodine in the periodictable, even though its atomic mass is slightly greater. Such anomalies are due to the relativeabundance of the “isotopes“ or varieties of each element. All the isotopes of a given elementhave the same number of protons, but differ in their number of neutrons, and hence in theiratomic mass. The isotopes of a given element have the same chemical properties but slightlydifferent physical properties. We now know that atomic number (the number of protons in thenucleus), not atomic mass number (the number of protons and neutrons), determineschemical behavior. 当德国化学家迈耶和(彼此独立的) 俄国的门捷列夫在1869 年和1870年第一次引入元素周期表 这一概念时，自然界还有三分之一的化学元素没被发现。然而根据周期性的物理和化学性质 的标示，两位化学家都富有预见性的在他们所分析的新元素应该的位置上留下空位。门捷列 夫比迈耶更加大胆，他甚至假定如果根据测定的原子质量把一个元素放置在元素周期表中显 示的是错误的位置，那么这个元素的原子质量也是错的。在某些情况下，这个假设是对的。 以金属铟为例，先前测量出的铟的原子质量在砷和硒之间。但是在周期表中，这两个元素之 间是没有缝隙的，门捷列夫建议铟的原子质量可以被改变成一个完全不同的质量，填充镉和 锡之间的空位。而事实上，后来的研究表明在元素周期表中，元素的顺序并不严格按照原子 质量排序。例如在周期表中碲在碘的前面，但是它的原子质量却要轻的多。这种反常现象是 由于每种元素的同位素或者变量的广泛存在。所有元素的同位素都具备相同的质子数，但是 中子数确不同。同位素具有相同的化学性质，但是物理性质有细微的差异，我们现在知道原 子序数(核原子核中的质子数) 决定了元素的化学性质，不是原子质量。 三、门捷列夫对未发现元素性质的预测 Mendeleyev went further than Meyer in another respect: he predicted the properties of sixelements yet to be discovered. For example, a gap just below aluminum suggested a newelement would be found with properties analogous to those of aluminum. Mendeleyevdesignated this element “eka-aluminum“ (eka is the Sanskrit word for “next“) and predictedits properties. Just five years later an element with the proper atomic mass was isolated andnamed gallium by its discoverer. The close correspondence between the observed properties ofgallium and Mendeleyevs predictions for eka-aluminum lent strong support to the periodiclaw. Additional support came in 1885 when eka-silicon, which had also been described inadvance by Mendeleyev, was discovered and named germanium. 门捷列夫在另一个方面上也比Meyer研究的更加深入：他预测了六种还没有被发现的元素的 性质。例如铝后面的一个空位暗示这个新元素将与铝的性质类似。门捷列夫将这个元素命名 为“类铝”(eka 这个词在梵语中的意思是 “下一个”) 而且还预测了它的性质。仅仅在五年后这一 元素的原子质量就被测量出来并独立成为一种元素，它被他的发现者命名为“镓”。镓所表现 出的特性和门捷列夫所预测的“次铝” 的性质的高度一致性为元素周期律提供了一个强有力的 支持。另一个支持的例证是在1885年也是同样由门捷列夫所预测的“次硅”。后来被人们发现 命名为锗。 四、元素周期表中稀有气体元素的发现 The structure of the periodic table appeared to limit the number of possible elements. It wastherefore quite surprising when John William Strut (Lord Rayleigh), discovered a gaseouselement in 1894 that did not fit into the previous classification scheme. A century earlier,Henry Cavendish had noted the existence of a residual gas when oxygen and nitrogen areremoved from air, but its importance had not been realized. Together with William Ramsay,Rayleigh isolated the gas (separating it from other substances into its pure state) and named itargon. Ramsay then studied a gas that was present in natural gas deposits and discovered tha