托福化學(xué)類閱讀文章翻譯，Development of the Periodic Table元素周期表的發(fā)展
文章詞匯words
元素element
族group
原子序數(shù)atomic number
同位素isotope
化學(xué)性質(zhì)chemical property
物理性質(zhì)physical property
原子atom
原子核nucleus
質(zhì)子proton
中子neutron
電子electron
稀有氣體rare gases
堿金屬alkali metal
文章翻譯translation
一、元素周期表出現(xiàn)的背景
The periodic table is a chart that reflects the periodic recurrence of chemical and physical properties of the elements when the elements are arranged in order of increasing atomic number (the number of protons in the nucleus). It is a monumental scientific achievement, and its development illustrates the essential interplay between observation, prediction, and testing required for scientific progress. In the 1800's scientists were searching for new elements. By the late 1860's more than 60 chemical elements had been identified, and much was known about their descriptive chemistry. Various proposals were put forth to arrange the elements into groups based on similarities in chemical and physical properties. The next step was to recognize a connection between group properties (physical or chemical similarities) and atomic mass (the measured mass of an individual atom of an element). When the elements known at the time were ordered by increasing atomic mass, it was found that successive elements belonged to different chemical groups and that the order of the groups in this sequence was fixed and repeated itself at regular intervals. It was a natural Idea to break up the series of elements at the points where the sequence of chemical groups to which the elements belonged began to repeat itself. Thus when the series of elements was written so as to begin a new horizontal row with each alkali metal, elements of the same groups were automatically assembled in vertical columns in a periodic table of the elements. This table was the forerunner of the modern table. 元素周期表是一個(gè)按照原子序數(shù)（原子核中的質(zhì)子數(shù)）排列的反映元素化學(xué)和物理性質(zhì)周期性再現(xiàn)的一個(gè)圖表。它是一個(gè)里程碑式的科學(xué)成就，它的發(fā)展闡明了科學(xué)發(fā)展中的觀察、預(yù)測(cè)、測(cè)試之間的必要關(guān)系。19世紀(jì)的科學(xué)家都在找尋新的元素。到了19世紀(jì)60年代晚期，有60多種元素被發(fā)現(xiàn)，人們對(duì)于他們的化學(xué)性質(zhì)也多有了解。基于這些元素的化學(xué)性質(zhì)和物理性質(zhì)的相似性，人們提出各種方案來對(duì)這些元素進(jìn)行分類。然后就是找到群族的元素性質(zhì)（物理或化學(xué)性質(zhì)的相似性）和原子質(zhì)量（測(cè)量的單個(gè)元素的原子質(zhì)量）之間的聯(lián)系。當(dāng)人們按照不斷增加的原子質(zhì)量的順序排列這些已知的元素時(shí)，發(fā)現(xiàn)連續(xù)的元素屬于不同的化學(xué)群族，群族的順序在這一序列中是固定的，并按照一定的間隔重復(fù)。很自然人們想到在這些元素所在群族的序列開始自我重復(fù)的哪一點(diǎn)上分開這一系列的元素。因此，當(dāng)這一系列的元素以堿金屬開始一段水平的一行，同族的元素被自動(dòng)聚集到元素周期表的垂直的一列當(dāng)中。這個(gè)圖表是現(xiàn)在元素周期表的前身。
二、元素周期表和原子質(zhì)量的關(guān)系
When the German chemist Lothar Meyer and (independently) the Russian Dmitry Mendeleyev first introduced the periodic table in 1869-70, one-third of the naturally occurring chemical elements had not yet been discovered. Yet both chemists were sufficiently farsighted to leave gaps where their analyses of periodic physical and chemical properties indicated that new elements should be located. Mendeleyev was bolder than Meyer and even assumed that if a measured atomic mass put an element in the wrong place in the table, the atomic mass was wrong. In some cases this was true. Indium, for example, had previously been assigned an atomic mass between those of arsenic and selenium. Because there is no space in the periodic table between these two elements, Mendeleyev suggested that the atomic mass of indium be changed to a completely different value, where it would fill an empty space between cadmium and tin. In fact, subsequent work has shown that in a periodic table, elements should not be ordered strictly by atomic mass. For example, tellurium comes before iodine in the periodic table, even though its atomic mass is slightly greater. Such anomalies are due to the relative abundance of the "isotopes" or varieties of each element. All the isotopes of a given element have the same number of protons, but differ in their number of neutrons, and hence in their atomic mass. The isotopes of a given element have the same chemical properties but slightly different physical properties. We now know that atomic number (the number of protons in the nucleus), not atomic mass number (the number of protons and neutrons), determines chemical behavior. 當(dāng)?shù)聡?guó)化學(xué)家邁耶和（彼此獨(dú)立的）俄國(guó)的門捷列夫在1869年和1870年第一次引入元素周期表這一概念時(shí)，自然界還有三分之一的化學(xué)元素沒被發(fā)現(xiàn)。然而根據(jù)周期性的物理和化學(xué)性質(zhì)的標(biāo)示，兩位化學(xué)家都富有預(yù)見性的在他們所分析的新元素應(yīng)該的位置上留下空位。門捷列夫比邁耶更加大膽，他甚至假定如果根據(jù)測(cè)定的原子質(zhì)量把一個(gè)元素放置在元素周期表中顯示的是錯(cuò)誤的位置，那么這個(gè)元素的原子質(zhì)量也是錯(cuò)的。在某些情況下，這個(gè)假設(shè)是對(duì)的。以金屬銦為例，先前測(cè)量出的銦的原子質(zhì)量在砷和硒之間。但是在周期表中，這兩個(gè)元素之間是沒有縫隙的，門捷列夫建議銦的原子質(zhì)量可以被改變成一個(gè)完全不同的質(zhì)量，填充鎘和錫之間的空位。而事實(shí)上，后來的研究表明在元素周期表中，元素的順序并不嚴(yán)格按照原子質(zhì)量排序。例如在周期表中碲在碘的前面，但是它的原子質(zhì)量卻要輕的多。這種反常現(xiàn)象是由于每種元素的同位素或者變量的廣泛存在。所有元素的同位素都具備相同的質(zhì)子數(shù)，但是中子數(shù)確不同。同位素具有相同的化學(xué)性質(zhì)，但是物理性質(zhì)有細(xì)微的差異，我們現(xiàn)在知道原子序數(shù)（核原子核中的質(zhì)子數(shù)）決定了元素的化學(xué)性質(zhì)，不是原子質(zhì)量。
三、門捷列夫?qū)ξ窗l(fā)現(xiàn)元素性質(zhì)的預(yù)測(cè)
Mendeleyev went further than Meyer in another respect: he predicted the properties of six elements yet to be discovered. For example, a gap just below aluminum suggested a new element would be found with properties analogous to those of aluminum. Mendeleyev designated this element "eka-aluminum" (eka is the Sanskrit word for "next") and predicted its properties. Just five years later an element with the proper atomic mass was isolated and named gallium by its discoverer. The close correspondence between the observed properties of gallium and Mendeleyev’s predictions for eka-aluminum lent strong support to the periodic law. Additional support came in 1885 when eka-silicon, which had also been described in advance by Mendeleyev, was discovered and named germanium. 門捷列夫在另一個(gè)方面上也比Meyer研究的更加深入：他預(yù)測(cè)了六種還沒有被發(fā)現(xiàn)的元素的性質(zhì)。例如鋁后面的一個(gè)空位暗示這個(gè)新元素將與鋁的性質(zhì)類似。門捷列夫?qū)⑦@個(gè)元素命名為“類鋁”（eka這個(gè)詞在梵語中的意思是“下一個(gè)”）而且還預(yù)測(cè)了它的性質(zhì)。僅僅在五年后這一元素的原子質(zhì)量就被測(cè)量出來并獨(dú)立成為一種元素，它被他的發(fā)現(xiàn)者命名為“鎵”。鎵所表現(xiàn)出的特性和門捷列夫所預(yù)測(cè)的“次鋁”的性質(zhì)的高度一致性為元素周期律提供了一個(gè)強(qiáng)有力的支持。另一個(gè)支持的例證是在1885年也是同樣由門捷列夫所預(yù)測(cè)的“次硅”。后來被人們發(fā)現(xiàn)命名為鍺。
四、元素周期表中稀有氣體元素的發(fā)現(xiàn)
The structure of the periodic table appeared to limit the number of possible elements. It was therefore quite surprising when John William Strut (Lord Rayleigh), discovered a gaseous element 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 are removed 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 it argon. Ramsay then studied a gas that was present in natural gas deposits and discovered that it was helium, an element whose presence in the Sun had been noted earlier in the spectrum of sunlight but that had not previously been known on Earth. Rayleigh and Ramsay postulated the existence of a new group of elements, and in 1898 other members of the series (neon, krypton, and xenon) were isolated. 元素周期表的框架限定了可能存在的元素的數(shù)量。因此當(dāng)約翰威廉姆斯杜爾特在1894年發(fā)現(xiàn)了一種氣體元素并不適合于先前的元素分類表格，這是相當(dāng)令人驚訝的。一個(gè)世紀(jì)以前亨利卡文迪許已經(jīng)注意到當(dāng)氧氣和氮?dú)鈴目諝庵斜环蛛x后仍然有剩余氣體存在，但是這種氣體的重要性并沒有被人們充分意識(shí)到。雷利和威廉姆拉姆齊共同分離出了一種氣體（將之與其他物質(zhì)隔離存放于一個(gè)純凈的環(huán)境）并將它命名為氬。拉姆齊后來研究了一種存在于天然氣沉積物中的氣體氦。這種元素存在于太陽中，并且早些時(shí)候在太陽光譜中出現(xiàn)時(shí)就被注意到，但是之前并沒有在地球上并沒有被發(fā)現(xiàn)過。雷利和拉姆齊認(rèn)為有一組新的元素存在，這組元素中的其他成員也在1898年被成功分離出來（氖，氪，氙）。