TPO 16 -2Development of the Periodic Table（自然/人文科学--物化/历史）
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. 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.
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.
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.
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.
解析：根据increasing atomic mass定位到倒数第3句，说当元素以increasing atomic mass（原子质量增加）的顺序排列时，发现连续的元素属于不同化学群，而且顺序固定，会有规律地重复。所以选C（with similar chemical properties倒数第5句）。A中alkali metals，B中repetition of same atomic masses，以及D中前后元素化学性质相似都没说。
解析：根据Meyer and Mendeleyev找到第1句，说他们最先引入周期表，两人通过对周期性的物理和化学性质的分析，都很有远见地在周期表中留空给新元素。所以题目中的decision就是在周期表中留空给新元素。A说他们自信地认为元素周期律适用于所有化学元素，根据decision可推断出来，A对。B原文Mendeleyev was bolder这句说如果将元素放错位置，原子量就是错的，与B说的内容不同。C中unwilling与原文相反。D中disagreement原文没说。
解析：本句后面说如果根据原子量将元素放错位置，原子量就是错的，即有些认为是真的信息（measured atomic mass）是错的，选B。
解析：根据changing...indium定位到第6句（Because there is...），说因为这两个元素间没有留位，所以indium的原子量应该是不同的值。而前面说如果根据原子量将元素放错位置，原子量就是错的，那这里的具体举例就证明了这个观点，选A
解析：根据tellurium定位到倒数第5句（For example, tellurium comes...）是一个例子，说明现象，并未说明原因，往前看，说元素不应该严格按照原子量排列。最后一句说是原子数而非原子量数决定化学行为。所以选D
解析：本句说刚好在al之下的空表明新元素的性质analogous to al的性质，两种元素处于上下位置，且下句说门捷列夫将这种元素定名为下一个al，那说明这两者可能有相似的性质，选C. analogous to 类似于
解析：根据gallium定位到第4句（Just five years later...），本句未说明这个发现支持什么，继续往后看，说支持了periodic law，选C
解析：插入句提到sequence of chemical groups... repeat itself，C前提到chemical groups和repeat itself，根据句意判断应该是首次出现，所以选C
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