不考氢氦锂铍硼的元素周期表

　　提起元素周期表，读过中学的朋友无一不晓，每个人都能流利地背诵“氢氦锂铍硼碳氮氧氟氖钠镁铝硅磷硫氯氩钾钙”。所以，当你遇到一篇主题为元素周期表的托福听力篇章时，一定内心暗喜，这还有啥难的？！

　　不，你高兴地太早了！

　　今天让我告诉你，元素周期表可不一定只考元素顺序！

　　首先，你得知道元素周期表的表达：Periodic Table [ˌpɪriˈɑːdɪk] [ˈteɪbl]

　　接下来，让我们跟随TPO8 Lecture4的思路来看看具体考察了哪些方面——

　　Prof先回顾了元素周期表中元素的构成特点，元素周期表是将元素按照共有的特质进行分类，并按照原子数递增排序，原子数即原子中质子的数量：

　　Prof：Ok, let’s look at our periodic table again. Ok, it groups elements into categories that share certain properties, right? And it is arranged according to increasing atomic number, which is…

　　Stu: The number of protons in each atom of an element.

　　【学科词表】

　　category [ˈkætəɡɔːri] n. 种类

　　property [ˈprɑːpərti] n. 性质

　　atomic [əˈtɑːmɪk] a. 原子的

　　proton [ˈproʊtɑːn] n. 质子

　　但是在早期的元素周期表中，43号元素一直存在空缺，直到1925年，一位名叫Ida Tacke的科学家声称带领其团队发现了有43个质子的元素，命名为Masurium，使用的方法是X射线光谱学测试：

　　Prof：Well, in early versions of the table, there was no symbol for an element with 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 in 1925, a team of chemists led by a scientist named Ida Tacke claimed that they had found element 43. They had been using a relatively new technology called X-ray spectroscopy, and they were using this to examine an ore sample. And they claimed that they’d found an element with 43 protons. And they named it Masurium.

　　【学科词表】

　　x-ray [ˈeks reɪ] n. x射线

　　spectroscopy [spekˈtrɑːskəpi] n. 光谱学

　　ore [ɔːr] n. 矿石

　　但这种方法不能从样本矿石中分理出足够多的Masurium，于是没人相信。直到1937年，另一支队伍首次用回旋加速器合成了拥有43个质子的元素，命名为Technetium，也就是现在元素周期表上的43号元素：

　　Prof：And they were never able to isolate enough Masurium to have a weighable sample to convince everyone of the discovery. So they were discredited. But then, 12 years later in 1937, a different team became the first to synthesize an element using a cyclotron. And that element had…

　　Stu: 43 protons?

　　Pro: That’s right, but they named it Technetium to emphasize that it was artificially created with technology.

　　【学科词表】

　　discredit [dɪsˈkredɪt] v. 不相信

　　synthesize [ˈsɪnθəsaɪz] v. 合成

　　cyclotron [ˈsaɪklətrɑːn] n. 回旋加速器

　　artificially [ˌɑːrtɪˈfɪʃəli] adv. 人工地

　　但43号元素不论命名如何，其特点是具有放射性，这意味着它会衰变成其他元素，也就解释了为什么它在元素周期表中一度消失不见。因此，如果43号元素曾在地球上存在，也早就衰变了，这就证明了Masurium科学家们的错误，以及Technetium科学家们的正确：

　　Prof：Now element 43, whether you call it Masurium or Technetium, is radioactive. Why does that matter? What is true of a radioactive element?

　　Stu: It decays, it turns into other elements. Oh, so does that explain why it was missing in the periodic table?

　　Pro: Exactly, because of its radioactive decay, element 43 doesn’t last very long. And therefore, if that ever had been present on Earth, it would have decayed ages ago. So the Masurium people were obviously wrong, and the Technetium people were right.

　　【学科词表】

　　radioactive [ˌreɪdioʊˈæktɪv] a. 放射性的

　　decay [dɪˈkeɪ] v. 衰退

　　不过现在我们已经知道43号元素可以从铀原子的自发裂变中产生，所以发现Masurium的小组也可能在矿石样本中发现了足够数量的铀，因此而发现了天然存在的43号元素，只不过它迅速衰变了。但时间已经过了这么久，当时也没有足够的证据发布，所以Prof宁愿相信43号元素被发现了两次，一次是在自然裂变中，一次是在实验室中被人工合成：

　　Prof：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 the ore samples. It’s just that once was generated from split Uranium, it decayed very quickly.

　　Stu：Should element 43 really be called Masurium?

　　Pro: Maybe, but you know it’s hard to tell for sure after all this time, if Ida Tacke’s group did discover element 43. They didn’t publish enough detail on their methods or instruments for us to know for sure. But I’d like to think 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 a laboratory.

　　【学科词表】

　　spontaneously [spɑːnˈteɪniəsli] adv. 自然地

　　split [splɪt] v. 分离

　　measurable [ˈmeʒərəbl] a. 可测量的

　　Uranium [juˈreɪniəm] n. 铀

　　fission [ˈfɪʃn] n. 分裂

　　所以现在大家知道元素周期表上的43号元素竟然还有一段曲折身世，同时也拓展了对于元素周期表的新认识~ 记得认真积累背诵以上学科生词*

　　作者介绍