Official 08 Set 6

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The Periodic Table of Elements

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In the beginning of the lecture a student asks a question about the periodic table. How does the story of element 43 answer her question?
  • A. By providing an example of an element whose place in the periodic table was moved

  • B. By providing an example of an element whose existence was predictable from the periodic table

  • C. By providing an example of an element which scientists predicted was formed from uranium

  • D. By providing an example of an element that can only be made artificially

显示答案 正确答案: B

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    NARRATOR:Listen to part of a lecture in a chemistry class. The professor has been discussing the periodic table of elements.

    MALE PROFESSOR:So … are there any questions?

    FEMALE STUDENT:Yes, em, professor Harrison, you were saying that the periodic table is predictive [hesitant upspeak]? What exactly does that mean?I mean I understand how it organizes the elements, but … where is the prediction?

    MALE PROFESSOR:OK, let's look at periodic table again.OK, it groups elements into categories that share certain properties, right?

    FEMALE STUDENT:Um-huh~

    MALE PROFESSOR:And it's arranged according to increasing atomic number, which is … ? [prompting for answer]

    FEMALE STUDENT:The number of protons in each atom of an element.

    MALE PROFESSOR:Right, well, early versions of the periodic table had gaps, missing elements.Every time you have one more proton you have another element, and then — oops — there’d be an atomic number for which there was no known element. And the uh prediction was that an element with that atomic number existed somewhere, but it just hadn’t been found yet.And its location in the table would tell you what properties it should have.It was really pretty exciting for scientists at that time to find these missing elements and confirm their predictive properties.

    Um actually, that reminds me of a, of a, of a very good example of all this … element 43.See on the table, the symbols for element 42 and 44.Well, in early versions of the table, there was no symbol for element 43 protons because no element with 43 protons had been discovered yet.So the periodic table had a gap between elements 42 and 44. And, then, uh, in 1925 a team of chemists led by a scientist named Ida Tacke claimed that they had found element 43.

    They had been, uh, using a relatively new technology called x-ray spectroscopy —and they were using this to examine an ore sample — and they claimed they’d found an element with 43 protons. And they named it masurium.

    MALE STUDENT:Um, professor Harrison, then, how come in my periodic table, here, element 43 is “Tc”, that's technetium, right?

    MALE PROFESSOR:OK, let me add that …[writing “technetium” on blackboard]Actually, um, that's the point I'm coming to.Hardly anyone believed that Tack has discovered the new element.X-ray spectroscopy was a new method at that time.And they were never able to isolate enough masurium to have a weighable sample, to convince everyone of their discovery, so they were discredited.

    But then, twelve years later, in 1937, a different team became the first to synthesize an element using a cyclotron. And that element had … [dramatic pause, leading the students to answer]

    MALE STUDENT:43 Protons?

    MALE PROFESSOR:That's right, but they named it Technetium to emphasize that it was artificially created with technology.And people thought that synthesizing this element, making it artificially was the only way to get it.We still haven't found it occurring in nature.Now, element 43 what they called Masurium or Technetium is radioactive.Why is that matter? What's true of radioactive element?

    FEMALE STUDENT:It decays? [adding to her answer] It turns into other elements? Oh [light dawning], so does that explain why it was missing in the periodic table?

    MALE PROFESSOR:Exactly. Because of its radioactive decay, element 43 doesn’t last very long … and therefore… if it ever had been present on Earth it would have decayed ages ago …[Reporting on what people believed then, not what he himself thinks] So the Masurium people were obviously wrong, and the Technetium people were right, right?Well, that was then. Now we know that element 43 does occur naturally—it can be naturally generated from uranium atoms that have spontaneously split.And guess what ... the ore sample the masurium group was working with had plenty of uranium in it—enough to split into measurable amounts of masurium.So Tacke’s team might very well have found small amounts of masurium in their ore sample. It’s just that once it was generated from split uranium, it decayed very quickly.

    And you know, here is an incredible irony.Ida Tack, the chemist led the Masurium team, when she was the first to suggest that Uranium could break up into smaller pieces but she didn't know that that was the defense of her own discovery of element 43.

    MALE STUDENT:So is my version of the periodic table wrong? Should element 43 really be called Masurium?

    MALE PROFESSOR:Maybe, but you know it‘s hard to tell for sure after all this time, if Ida Tack’s group did discover element 43.They didn't, um, publish enough detail on their methods or instruments for us to know for sure.But I'd like to think that element 43 was discovered twice, as Masurium, it was the first element discovered that occurs in nature only from spontaneous fission, and as Technetium, it was the first element discovered in laboratory.And of course, it was an element the periodic table let us to expect existed before anyone had found it or made it.

  • 旁白:听一段化学课的讲座。教授在讨论元素周期表。

    教授:大家有什么问题吗?

    学生:Harrison教授,你说元素周期表是可预测的?那究竟是什么意思?我明白它如何组织这些元素,但是预测在哪里呢?

    教授:好的,让我们再看一下周期表。它把元素按它们共有的特质分类对吗?

    学生:是的。

    教授:它按原子数递增排序,原子数是。。。

    学生:是元素原子中的质子数。

    教授:对,早期版本的周期表有空缺,丢失的元素。多一个质子,就成了另一种元素。但是有相应的原子数,却不知道相应的元素是什么。预测正是指那个原子数确定但还仍未被发现的元素。它在表中的位置可以告诉我们它应该拥有的特性。对那个时候的科学家来说找到这些缺失的元素并确认它们预测特性是件很令人激动的事。

    事实上,这让我想起来一个非常好的例子,第43号元素。看表格中42号及44号元素的符号。在早期版本的周期表中,43号元素没有符号,因为那时有43个质子数的元素尚未被发现。所以周期表上在42和44号元素中有空缺,之后在1925年,由一位名叫Ida Tack的科学家带领的化学家团队声称他们找到了43号元素。

    他们正在使用一项相对较新的技术X射线光谱学检查一种矿石样本,他们称找到了有43个质子的元素,命名为Masuria。

    学生:Harrison教授,在我们元素周期表中43号元素是Tc是怎么来的呢?那是锝对吗?

    教授:好吧,我补充一下...实际上,我马上要讲到这点。当时几乎没有人相信Tack发现了新元素。因为那时X射线光谱学是新方法。他们无法分离出足够多的Masurium作为使人信服的样本,所以他们没有被人们相信。

    但是后来,12年后,1937年,另一支队伍成为首次使用回旋加速器合成元素的团队。合成这种元素有。。。

    学生:43个质子?

    教授:对,但是他们将它命名为Technetium以强调它是由技术人工合成的。人们认为人工合成这一元素是唯一得到它的方法。我们至今无法在自然界中找到它。43号元素无论称为Masurium还是Technetium,是具有放射性的。这有什么关系呢?放射性元素的是怎样的呢?

    学生:放射性元素会衰变,它会转变成其他元素,哦,这是不是解释了为什么它在元素周期表中曾一度缺失?

    教授:正是。由于43号元素放射性的衰变,它不能长久存在,因此,如果它曾经在地球上存在过,也早就衰变了。所以那时发现Masurium的人显然错了,而发现Technetium的人是对的。是吧?不过那是以前,现在我们知道43号元素在自然中确实存在,它可以从铀原子自发的裂变中自然产生。猜怎么着?masurium小组研究的矿石样品中含有大量的铀,足够分裂成可测量的masurium。所以Tack的团队可能真的在矿石样品中发现了小量masurium ,只是它一从铀裂变中产生后就迅速衰变了。

    你们知道么,这很讽刺。发现Masurium的化学家Ida Tack,她是第一个提出铀可以分解成小片,但她不知道这是对她自己发现的43号元素的辩护。

    学生:所以是我们这版的周期表错了?43号元素应该称为Masurium?

    教授:也许,但是你们知道已经过去那么久这很难说Ida Tack 的队伍是否发现了43 号元素。他们没有发布关于他们使用的方法或是仪器的足够多的细节信息使我们确认。但是我愿意认为43 号元素被两次发现。作为Masurium,它是首次从自然裂变中发生的自然元素,作为Technetium,它首次在实验室发现。当然,它是一种在被任何人发现或是制造之前,周期表让我们相信它存在的元素。

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    题型分类:细节题
    题干分析:关键词how确定为细节题,根据in the beginning of the lecture定位文章内容
    原文定位:Um, actually, that reminds me of a ... of a very good example of all these, element 43. See on the table, the symbols for elements 42 and 44. Well, in early versions of the table, there was no symbol for an element 43 protons because no element with 43 protons had been discovered yet. 
    选项分析:

    教授先说解释了 element 的 predictable。又说 Um, actually, that reminds other, other very good example of all these, element 43. See on the table, the symbol for element 42 and 44,43 号元素是predictable 的。选项B正确。

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The Periodic Table of Elements

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