[請益] TPO 16 DEVELOPMENT OF THE PERIODIC TABLE

看板TOEFL_iBT (TOEFL_iBT托福)作者tom192180 (tom510558)時間14年前 (2011/08/30 08:40)推噓0(0推 0噓 6→)

留言6則, 2人參與討論串1/1

不好意思，想請問大家這篇。第二段: 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. 6. 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 ○iodine is less common than tellurium ○both iodine and tellurium have no isotopes ○the chemical behavior of tellurium is highly variable ○the atomic number of tellurium is smaller than that of iodine 答案是D，可是要從哪推論出來，我左看右看都看不出端倪= = -- ※ 發信站: 批踢踢實業坊(ptt.cc) ◆ From: 122.126.25.123