Theperiodictable is achartthat reflects theperiodicrecurrence of chemical andphysicalproperties of the elements when the elements are arranged in order of increasingatomicnumber(the number of protons in thenucleus). It is amonumentalscientificachievement, and itsdevelopmentillustrates theessentialinterplaybetweenobservation, prediction, and testing required forscientificprogress. 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 theirdescriptivechemistry. Various proposals were put forth toarrangethe elements into groups based on similarities in chemical andphysicalproperties. The next step was torecognizea connection between group properties (physicalor chemical similarities) andatomicmass(the measuredmassof anindividualatomof anelement). When the elements known at the time were ordered by increasingatomicmass, it was found thatsuccessiveelements belonged to different chemical groups and that the order of the groups in thissequencewas fixed and repeated itself atregularintervals. Thus when theseriesof elements was written so as to begin a newhorizontalrow with eachalkalimetal, This table was theforerunnerof the modern table.

When the German chemist Lothar Meyer and (independently) the Russian Dmitry Mendeleyev first introduced theperiodictable in 1869-70, one-third of the naturally occurring chemical elements had not yet been discovered. Yet both chemists weresufficientlyfarsighted to leave gaps where their analyses ofperiodicphysicaland chemical properties indicated that new elements should be located. Mendeleyev was bolder than Meyer andevenassumed that if a measuredatomicmassput anelementin the wrong place in the table, theatomicmasswas wrong. In some cases this was true. Indium, for example, hadpreviouslybeen assigned anatomicmassbetween those ofarsenicand selenium. Because there is nospacein theperiodictable between these two elements, Mendeleyev suggested that theatomicmassof indium be changed to a completely different value, where it would fill an emptyspacebetween cadmium and tin. In fact,subsequentwork has shown that in aperiodictable, elements should not be ordered strictly byatomicmass. For example, tellurium comes before iodine in theperiodictable,eventhough itsatomicmassisslightlygreater. Such anomalies aredueto therelativeabundanceof the "isotopes" or varieties of eachelement. All the isotopes of agivenelementhave the same number of protons, but differ in their number of neutrons, and hence in theiratomicmass. The isotopes of agivenelementhave the same chemical properties butslightlydifferentphysicalproperties. We now know thatatomicnumber (the number of protons in thenucleus), notatomicmassnumber (the number of protons and neutrons), determines chemicalbehavior.

Mendeleyev went further than Meyer in another respect: he predicted the properties of six elements yet to be discovered. For example, agapjust belowaluminumsuggested a newelementwould be found with propertiesanalogousto those ofaluminum. Mendeleyev designated thiselement"eka-aluminum" (eka is the Sanskrit word for   "next") and predicted its properties. Just five years later anelementwith theproperatomicmasswasisolatedand named gallium by its discoverer. The closecorrespondencebetween the observed properties of gallium and Mendeleyev's predictions for eka-aluminum lent strong support to theperiodiclaw. Additionalsupport came in 1885 when eka-silicon, which had also been described inadvanceby Mendeleyev, was discovered and named germanium.

The structure of theperiodictable appeared to limit the number of possible elements. It wasthereforequite surprising when John William Strut( Lord Rayleigh, discovered agaseouselementin 1894 that did not fit into thepreviousclassificationscheme. Acenturyearlier, Henry Cavendish hadnotedtheexistenceof a residual gas whenoxygenandnitrogenare removed fromair, but its importance had not been realized. Together with William Ramsay, Rayleighisolatedthe gas (separating it from other substances into itspurestate) and named itargon. Ramsay then studied a gas that was present in natural gas deposits and discovered that it washelium, anelementwhose presence in the Sun had beennotedearlier in thespectrumof sunlight but that had notpreviouslybeen known on Earth. Rayleigh and Ramsay postulated theexistenceof a new group of elements, and in 1898 other members of theseries(neon, krypton, and xenon) wereisolated.

Questions:
question_stem: The phrase interplay in the passage is closest in meaning to
choices: tag: A
text: sequence

tag: B
text: interpretation

tag: C
text: requirement

tag: D
text: interaction
answer_key: D
explanation: D interplay: 相互作用。A 是顺序；B 是翻译，诠释；C 是要求；D 是相互作用。所以 D 的 interaction 正确。

question_stem: According to paragraph 1, what pattern did scientists notice when the known elements were written in order of increasing atomic mass?
choices: tag: A
text: The elements of the group of alkali metals were the first elements in the order of increasing atomic mass.

tag: B
text: Repetition of the same atomic masses for elements in different groups appeared.

tag: C
text: Elements with similar chemical properties appeared in the listing at regular intervals.

tag: D
text: Elements were chemically most similar to those just before and after them in the order.
answer_key: C
explanation: C 以 increasing atomic mass 做关键词定位至倒数第三句，说把元素按照原子量增加的顺序排布，发现相邻元素属于不同的族，族的顺序是固定的，每隔固定数量的元素会重现。所以正确答案是 C。A 的 alkali metals，B 的 same atomic mass 原文都没说；D 说相邻元素性质相近与原文相反。

question_stem: In paragraph 2, what is the author's purpose in presenting the information about the decision by Meyer and Mendeleyev to leave gaps in the periodic table?
choices: tag: A
text: To illustrate their confidence that the organizing principles of the periodic table would govern the occurrence of all chemical elements

tag: B
text: To indicate that some of their analyses of periodic physical and chemical properties were later found to be wrong

tag: C
text: To support the idea that they were unwilling to place new elements in the periodic table

tag: D
text: To indicate how they handled their disagreement about where to place new elements
answer_key: A
explanation: A, 修辞目的题，先找到两个人名，说两个人都非常有远见，在周期表中给没发现的元素留了空隙，也就是 A 说的他们足够自信认为元素周期律适用于所有元素；B 的 wrong 和 C 的 unwilling 都跟原文说反；D 的 disagreement 原文没说。

question_stem: What reason does the author provide for the claim that Mendeleyev was bolder than Meyer?
choices: tag: A
text: Mendeleyev corrected incorrect information Meyer had proposed.

tag: B
text: Mendeleyev assumed that some information believed to be true about the elements was incorrect.

tag: C
text: Mendeleyev argued that Meyer had not left enough gaps in the periodic table.

tag: D
text: Mendeleyev realized that elements were not ordered by atomic mass in the periodic table.
answer_key: B
explanation: B 先找到两个人名，说门捷列夫比梅伊尔更胆儿大，他推测如果用来在周期表中排序的原子量与元素周期律互相冲突的时候，就说明原子量错了，也就是选项 B 说的门捷列夫认为以前被大家所认识到的一些东西是错的。两个人的意见是一样的，只是门捷列夫更进一步，所以 A 和 C 说两者的意见有差异不对；D 说不是按原子量排序的错。

question_stem: According to paragraph 2, why did Mendeleyev suggest changing the atomic mass of indium?
choices: tag: A
text: Because indium did not fit into the periodic table in the place predicted by its atomic mass.

tag: B
text: Because there was experimental evidence that the atomic mass that had been assigned to indium was incorrect.

tag: C
text: Because there was an empty space between cadmium and tin in the periodic table.

tag: D
text: Because the chemical properties of indium were similar to those of arsenic and selenium.
answer_key: A
explanation: A 以 changing the atomic mass of indium 做关键词定位至第六句，说由于元素周期表中砷和硒之间没有空位，所以铟的原子量是错的。因为前面说如果原子量把元素放错了位置，就说明原子量是错的，后一句是为了证明这个观点的，所以答案是 A。B 的 experimental evidence 和 D 的化学性质相似原文都没说；C 有 space 与原文相反。

question_stem: It can be inferred from paragraph 2 that tellurium comes before iodine in the periodic table even though tellurium's atomic mass is slightly greater because
choices: tag: A
text: iodine is less common than tellurium

tag: B
text: both iodine and tellurium have no isotopes

tag: C
text: the chemical behavior of tellurium is highly variable

tag: D
text: the atomic number of tellurium is smaller than that of iodine
answer_key: D
explanation: D 以 tellerium coms before iodine 做关键词定位至倒数第五句 for example 处，但这句话只是一个例子，所以往前看，说元素不应该严格按照原子量排列，而且最后一句又说决定元素化学性质的是原子序数，不是原子量，也就是应该按照原序数量排列，所以答案 D 正确。A 谁 common 谁不 common，B 有没有同位素还有 C 的化学性质多变没有信息能推出。

question_stem: The phrase “abundance” in the passage is closest in meaning to
choices: tag: A
text: weight

tag: B
text: requirement

tag: C
text: plenty

tag: D
text: sequence
answer_key: C
explanation: C abundance: 充裕，丰富。A 是重量；B 是要求；C 是许多，大量；C 是顺序。答案是 C 的 plenty。

question_stem: The phrase “analogous to” in the passage is closest in meaning to
choices: tag: A
text: predicted by

tag: B
text: expected of

tag: C
text: similar to

tag: D
text: superior to
answer_key: C
explanation: C analogous to: 可类比的，相似的。A 是由…预测；B 是对…期望；C 是和…相似；D 是比…优越。所以答案 C 的 similar to 正确。

question_stem: Paragraph 3 suggests that Mendeleyev predicted the properties of eka-aluminum on the basis of
choices: tag: A
text: the atomic mass of aluminum

tag: B
text: the position of the gap in the periodic table that eka-aluminum was predicted to fill

tag: C
text: the similarity of eka-aluminum to the other five missing elements

tag: D
text: observation of the properties of gallium
answer_key: B
explanation: B 以 eka-aluminum 做关键词定位至第三句，但这句话只说了预测了 eka 的性质，没说根据什么预测的，看上一句，说 eka 是铝之下的那个空格里的元素，而且跟铝性质相似，所以答案是 B，eka 要填的那个空格。A 铝的原子量 C 另外五个没发现的元素 D 的 gallium 原文都没说。

question_stem: It can be inferred from paragraph 3 that the significance of the discovery of gallium was that it supported which of the following?
choices: tag: A
text: The idea that aluminum was correctly placed in the periodic table.

tag: B
text: Mendeleyev's prediction that eka-silicon would be discovered next.

tag: C
text: The organizing principle of the periodic table.

tag: D
text: The idea that unknown elements existed.
answer_key: C
explanation: C gallium 做关键词定位至倒数第三句，但这句话只是说命名为 GA，没说支持什么，往下看说 GA 的发现支持了元素周期律，而问题刚好是问 GA 的发现支持了什么，所以答案是 C，元素周期表的组成规律，也就是元素周期律。

question_stem: Which of the sentences below best expresses the essential information in the highlighted sentence in the passage? Incorrect choices change the meaning in important ways or leave out essential information.
choices: tag: A
text: Ramsay found evidence of helium in the spectrum of sunlight before he discovered that the element was also contained in natural gas deposits on Earth.

tag: B
text: Ramsay thought he had discovered a new element present in natural gas deposits, but he was wrong since that element had been previously observed elsewhere on Earth.

tag: C
text: After Ramsay had discovered a new element, called helium, in natural gas deposits on Earth, he also found evidence of its presence in the Sun.

tag: D
text: Ramsay later discovered that helium, an element that was already known to be present in the Sun, was also present in natural gas deposits on Earth.
answer_key: D
explanation: D : 原文的结构是 R 研究了一种气体，并且发现这种气体是氦，所以答案是 D。A 完全搞乱了原文的结构，氦在太阳光谱中不是 R 发现的；B 的转折关系错；C 和 A 的错误相似，氦在太阳光谱中不是 R 发现的。

question_stem: The word “postulated” in the passage is closest in meaning to
choices: tag: A
text: hypothesized

tag: B
text: discovered

tag: C
text: reported

tag: D
text: generated
answer_key: A
explanation: A，postulate: 推断，假定。A 是假设，假定；B 是发现；C 是报告；D 是声称。所以 A 的 hypothesize 正确。