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  • Periodic Table: Scientists Propose New Way Of Ordering The Elements周期表:科学家提出了排列元素的新方法

    The periodic table of the elements, principally created by the Russian chemist, Dmitry Mendeleev (1834-1907), celebrated1 its 150th anniversary last year. It would be hard to overstate its importance as an organising principle in chemistry – all budding chemists become familiar with it from the earliest stages of their education.


    Given the table’s importance, one might be forgiven for thinking that the ordering of the elements were no longer subject to debate. However, two scientists in Moscow, Russia, have recently published a proposal for a new order.


    Let’s first consider how the periodic table was developed. By the late 18th century, chemists were clear about the difference between an element and a compound: elements were chemically indivisible (examples are hydrogen, oxygen) whereas compounds consisted of two or more elements in combination, having properties quite distinct from their component2 elements. By the early 19th century, there was good circumstantial evidence for the existence of atoms. And by the 1860s, it was possible to list the known elements in order of their relative atomic mass – for example, hydrogen was 1 and oxygen 16.


    Simple lists, of course, are one-dimensional in nature. But chemists were aware that certain elements had rather similar chemical properties: for example lithium, sodium3 and potassium or chlorine, bromine and iodine4. Something seemed to repeat and by placing chemically similar elements next to each other, a two-dimensional table could be constructed. The periodic table was born.


    Nick Norman

    Importantly, Mendeleev’s periodic table had been derived6 empirically based on the observed chemical similarities of certain elements. It would not be until the early 20th century, after the structure of the atom had been established and following the development of quantum theory, that a theoretical understanding of its structure would emerge.


    Elements were now ordered by atomic number (the number of positively7 charged particles called protons in the atomic nucleus), rather than by atomic mass, but still also by chemical similarities. But the latter now followed from the arrangement of electrons repeating in so-called “shells” at regular intervals8. By the 1940s, most textbooks featured a periodic table similar to ones we see today.


    It would be understandable to think that this would be the end of the matter. Not so, however. A simple search of the internet will reveal all sorts of versions of the periodic table. There are short versions, long versions, circular versions, spiral versions and even three-dimensional versions. Many of these, to be sure, are simply different ways of conveying the same information but there continue to be disagreements about where some elements should be placed.


    The precise placement of certain elements depends on which particular properties we wish to highlight. Thus, a periodic table which gives primacy to the electronic structure of atoms will differ from tables for which the principal criteria9 are certain chemical or physical properties.


    These versions don’t differ by much, but there are certain elements – hydrogen for example – which one might place quite differently according to the particular property one wishes to highlight. Some tables place hydrogen in group 1 whereas in others it sits at the top of group 17; some tables even have it in a group on its own.


    Rather more radically10, however, we can also consider ordering the elements in a very different way, one which does not involve atomic number or reflect electronic structure – reverting11 to a one-dimensional list.


    The latest attempt to order elements in this manner was recently published in the Journal of Physical Chemistry by scientists Zahed Allahyari and Artem Oganov. Their approach, building on the earlier work of others, is to assign to each element what’s called a Mendeleev Number (MN). There are several ways to derive5 such numbers, but the latest study uses a combination of two fundamental quantities which can be measured directly: an element’s atomic radius12 and a property called electronegativity which describes how strongly an atom attracts electrons to itself.

    科学家Zahed Allahyari和Artem Oganov最近在《物理化学杂志》上发表了用这种方式排列元素的最新尝试。他们的方法是在其他人早期工作的基础上,给每个元素分配所谓的门捷列夫数(MN)。有几种方法可以得出这样的数字,但最新的研究使用了两个可以直接测量的基本量的组合:元素的原子半径和一种称为电负性的特性,该特性描述了原子吸引电子的强度。

    If one orders the elements by their MN, nearest neighbours have, unsurprisingly, rather similar MNs. But of more use is to take this one step further and construct a two-dimensional grid13 based on the MN of the constituent14 elements in so called “binary15 compounds”. These are compounds composed of two elements, such as sodium chloride, NaCl.


    What is the benefit of this approach? Importantly, it can help to predict the properties of binary compounds that haven’t been made yet. This is useful in the search for new materials that are likely be needed for both future and existing technologies. In time, no doubt, this will be extended to compounds with more than two elemental components16.


    A good example of the importance of the search for new materials can be appreciated by considering the periodic table shown in the figure below. This table illustrates17 not only the relative abundance of the elements (the larger the box for each element, the more of it there is) but also highlights potential supply issues relevant to technologies that have become ubiquitous and essential in our daily lives.


    Take mobile phones, for instance. All of the elements used in their manufacture are identified with the phone icon18 and you can see that several required elements are becoming scarce – their future supply is uncertain. If we are to develop replacement19 materials which avoid the use of certain elements, the insights gained from ordering elements by their MN may prove valuable in that search.


    After 150 years, we can see that periodic tables are not just a vital educational tool, they remain useful for researchers in their quest for essential new materials. But we should not think of new versions as replacements20 for earlier depictions. Having many different tables and lists only serves to deepen our understanding of how elements behave.


     10级    双语 


    1 celebrated [ˈselɪbreɪtɪd] iwLzpz   第8级
    • He was soon one of the most celebrated young painters in England. 不久他就成了英格兰最负盛名的年轻画家之一。
    • The celebrated violinist was mobbed by the audience. 观众团团围住了这位著名的小提琴演奏家。
    2 component [kəmˈpəʊnənt] epSzv   第7级
    • Each component is carefully checked before assembly. 每个零件在装配前都经过仔细检查。
    • Blade and handle are the component parts of a knife. 刀身和刀柄是一把刀的组成部分。
    3 sodium [ˈsəʊdiəm] Hrpyc   第8级
    • Out over the town the sodium lights were lit. 在外面,全城的钠光灯都亮了。
    • Common salt is a compound of sodium and chlorine. 食盐是钠和氯的复合物。
    4 iodine [ˈaɪədi:n] Da6zr   第10级
    • The doctor painted iodine on the cut. 医生在伤口上涂点碘酒。
    • Iodine tends to localize in the thyroid. 碘容易集于甲状腺。
    5 derive [dɪˈraɪv] hmLzH   第7级
    • We derive our sustenance from the land. 我们从土地获取食物。
    • We shall derive much benefit from reading good novels. 我们将从优秀小说中获得很大好处。
    6 derived [dɪ'raɪvd] 6cddb7353e699051a384686b6b3ff1e2   第7级
    vi.起源;由来;衍生;导出v.得到( derive的过去式和过去分词 );(从…中)得到获得;源于;(从…中)提取
    • Many English words are derived from Latin and Greek. 英语很多词源出于拉丁文和希腊文。 来自《简明英汉词典》
    • He derived his enthusiasm for literature from his father. 他对文学的爱好是受他父亲的影响。 来自《简明英汉词典》
    7 positively [ˈpɒzətɪvli] vPTxw   第7级
    • She was positively glowing with happiness. 她满脸幸福。
    • The weather was positively poisonous. 这天气着实讨厌。
    8 intervals ['ɪntevl] f46c9d8b430e8c86dea610ec56b7cbef   第7级
    n.[军事]间隔( interval的名词复数 );间隔时间;[数学]区间;(戏剧、电影或音乐会的)幕间休息
    • The forecast said there would be sunny intervals and showers. 预报间晴,有阵雨。
    • Meetings take place at fortnightly intervals. 每两周开一次会。
    9 criteria [kraɪ'tɪərɪə] vafyC   第12级
    • The main criterion is value for money. 主要的标准是钱要用得划算。
    • There are strict criteria for inclusion in the competition. 参赛的标准很严格。
    10 radically ['rædikəli] ITQxu   第7级
    • I think we may have to rethink our policies fairly radically. 我认为我们可能要对我们的政策进行根本的反思。
    • The health service must be radically reformed. 公共医疗卫生服务必须进行彻底改革。
    11 reverting [rɪˈvɜ:tɪŋ] f5366d3e7a0be69d0213079d037ba63e   第9级
    恢复( revert的现在分词 ); 重提; 回到…上; 归还
    • The boss came back from holiday all relaxed and smiling, but now he's reverting to type. 老板刚度假回来时十分随和,满面笑容,现在又恢复原样了。
    • The conversation kept reverting to the subject of money. 谈话的内容总是离不开钱的事。
    12 radius [ˈreɪdiəs] LTKxp   第7级
    • He has visited every shop within a radius of two miles. 周围两英里以内的店铺他都去过。
    • We are measuring the radius of the circle. 我们正在测量圆的半径。
    13 grid [grɪd] 5rPzpK   第9级
    • In this application, the carrier is used to encapsulate the grid. 在这种情况下,要用载体把格栅密封起来。
    • Modern gauges consist of metal foil in the form of a grid. 现代应变仪则由网格形式的金属片组成。
    14 constituent [kənˈstɪtjuənt] bpxzK   第7级
    • Sugar is the main constituent of candy. 食糖是糖果的主要成分。
    • Fibre is a natural constituent of a healthy diet. 纤维是健康饮食的天然组成部分。
    15 binary [ˈbaɪnəri] jybzWZ   第9级
    • Computers operate using binary numbers. 计算机运行运用二进位制。
    • Let us try converting the number itself to binary. 我们试一试,把这个数本身变成二进制数。
    16 components [kəm'pəʊnənt] 4725dcf446a342f1473a8228e42dfa48   第7级
    (机器、设备等的)构成要素,零件,成分; 成分( component的名词复数 ); [物理化学]组分; [数学]分量; (混合物的)组成部分
    • the components of a machine 机器部件
    • Our chemistry teacher often reduces a compound to its components in lab. 在实验室中化学老师常把化合物分解为各种成分。
    17 illustrates [ˈiləstreits] a03402300df9f3e3716d9eb11aae5782   第7级
    给…加插图( illustrate的第三人称单数 ); 说明; 表明; (用示例、图画等)说明
    • This historical novel illustrates the breaking up of feudal society in microcosm. 这部历史小说是走向崩溃的封建社会的缩影。
    • Alfred Adler, a famous doctor, had an experience which illustrates this. 阿尔弗莱德 - 阿德勒是一位著名的医生,他有过可以说明这点的经历。 来自中级百科部分
    18 icon [ˈaɪkɒn] JbxxB   第8级
    • They found an icon in the monastery. 他们在修道院中发现了一个圣像。
    • Click on this icon to align or justify text. 点击这个图标使文本排齐。
    19 replacement [rɪˈpleɪsmənt] UVxxM   第7级
    • We are hard put to find a replacement for our assistant. 我们很难找到一个人来代替我们的助手。
    • They put all the students through the replacement examination. 他们让所有的学生参加分班考试。
    20 replacements [rɪp'leɪsmənts] 1f6e0d51ec9f57961e86b4aa2e91ef29   第7级
    n.代替( replacement的名词复数 );替换的人[物];替代品;归还
    • They infiltrated behind the lines so as to annoy the emery replacements. 他们渗透敌后以便骚扰敌军的调度。 来自辞典例句
    • For oil replacements, cheap suddenly looks less of a problem. 对于石油的替代品来说,价格变得无足轻重了。 来自互联网

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