周期表:科學家提出了排列元素的新方法

周期表:科學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), celebrated 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.

元素周期表主要是由俄國化學家德米特里·門捷列夫(1834-1907)發(fā)明的，去年慶祝了它的150周年紀念日。在化學中，它作為一種組織原理的重要性怎么說都不為過——所有剛出道的化學家在他們受教育的最初階段就已經(jīng)熟悉它了。

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.

考慮到表的重要性，人們可能會認為元素的順序不再是辯論的主題，這是可以原諒的。然而，俄羅斯莫斯科的兩位科學家最近發(fā)表了一份關(guān)于新排序的建議。

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 component 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.

讓我們首先考慮元素周期表是如何形成的。到18世紀晚期，化學家們已經(jīng)清楚了元素和化合物之間的區(qū)別:元素在化學上是不可分的(例如氫、氧)，而化合物是由兩種或兩種以上的元素組合而成，具有與其組成元素截然不同的性質(zhì)。到19世紀初，已經(jīng)有了很好的間接證據(jù)證明原子的存在。到了19世紀60年代，人們可以按照相對原子質(zhì)量的順序列出已知元素——例如，氫是1，氧是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, sodium and potassium or chlorine, bromine and iodine. 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.

當然，簡單的列表本質(zhì)上是一維的。但化學家們意識到某些元素具有相當相似的化學性質(zhì):例如鋰、鈉和鉀或氯、溴和碘。有些東西似乎是重復的，通過把化學成分相似的元素放在一起，就可以建立一個二維表格。元素周期表誕生了。

Nick Norman

Importantly, Mendeleev’s periodic table had been derived 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.

重要的是，門捷列夫的元素周期表是根據(jù)觀察到的某些元素的化學相似性根據(jù)經(jīng)驗推導出來的。直到20世紀初，在原子結(jié)構(gòu)被確定之后，隨著量子理論的發(fā)展，才出現(xiàn)了對原子結(jié)構(gòu)的理論理解。

Elements were now ordered by atomic number (the number of positively 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 intervals. By the 1940s, most textbooks featured a periodic table similar to ones we see today.

元素現(xiàn)在按原子序數(shù)(原子核中被稱為質(zhì)子的帶正電的粒子的數(shù)量)排序，而不是按原子質(zhì)量排序，但仍然按化學相似性排序。但現(xiàn)在，電子在所謂的“殼層”中按照一定的間隔重復排列，形成了后者。到20世紀40年代，大多數(shù)教科書都有與我們今天看到的元素周期表類似的元素周期表。

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.

認為這件事將就此結(jié)束，這是可以理解的。但事實并不是這樣的。在互聯(lián)網(wǎng)上簡單地搜索一下，就會發(fā)現(xiàn)元素周期表的各種版本。有短版本，長版本，圓形版本，螺旋版本，甚至三維版本?？梢钥隙ǖ氖?，其中許多只是傳達相同信息的不同方式，但對于某些元素應該放在哪里仍然存在分歧。

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 criteria are certain chemical or physical properties.

某些元素的精確位置取決于我們希望突出顯示的特定屬性。因此，以原子的電子結(jié)構(gòu)為首要標準的周期表與以某些化學或物理性質(zhì)為主要標準的周期表是不同的。

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.

這些版本差別不大，但有一些元素——比如氫——根據(jù)人們想要強調(diào)的特定性質(zhì)，它們的位置可能會有很大的不同。有些表格把氫放在第一組，而另一些則放在第17組的頂部;有些表甚至把它單獨放在一個組中。

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

然而，更根本的是，我們還可以考慮以一種非常不同的方式對元素進行排序，一種不涉及原子序數(shù)或反映電子結(jié)構(gòu)的排序——恢復到一維列表。

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 derive such numbers, but the latest study uses a combination of two fundamental quantities which can be measured directly: an element’s atomic radius and a property called electronegativity which describes how strongly an atom attracts electrons to itself.

科學家Zahed Allahyari和Artem Oganov最近在《物理化學雜志》上發(fā)表了用這種方式排列元素的最新嘗試。他們的方法是在其他人早期工作的基礎上，給每個元素分配所謂的門捷列夫數(shù)(MN)。有幾種方法可以得出這樣的數(shù)字，但最新的研究使用了兩個可以直接測量的基本量的組合:元素的原子半徑和一種稱為電負性的特性，該特性描述了原子吸引電子的強度。

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 grid based on the MN of the constituent elements in so called “binary compounds”. These are compounds composed of two elements, such as sodium chloride, NaCl.

如果我們按元素的MN來排序，那么最鄰近的元素的MN也會非常相似。但更有用的是更進一步，以所謂的“二元化合物”中組成元素的MN為基礎構(gòu)建一個二維網(wǎng)格。這些化合物由兩種元素組成，如氯化鈉(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 components.

這種方法的好處是什么?重要的是，它可以幫助預測尚未生成的二元化合物的性質(zhì)。這對于尋找未來和現(xiàn)有技術(shù)可能需要的新材料是很有用的。毫無疑問，隨著時間的推移，這種方法將擴展到含有兩種以上元素的化合物。

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 illustrates 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.

一個關(guān)于尋找新材料的重要性的好例子可以通過考慮下表中所示的元素周期表來理解。這個表格不僅說明了元素的相對豐度(每個元素的盒子越大，它就越多)，而且還強調(diào)了與我們?nèi)粘Ｉ钪袩o處不在和必不可少的技術(shù)相關(guān)的潛在供應問題。

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

以手機為例。所有在制造過程中使用的元素都用手機圖標標識，你可以看到一些必需的元素正在變得稀缺——它們的未來供應是不確定的。如果我們要開發(fā)避免使用某些元素的替代材料，那么根據(jù)元素的MN排序所獲得的洞見可能在這一探索中被證明是有價值的。

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 replacements for earlier depictions. Having many different tables and lists only serves to deepen our understanding of how elements behave.

150年后，我們可以看到，元素周期表不僅是一種重要的教育工具，在研究人員尋找重要新材料的過程中，它們?nèi)匀缓苡杏?。但我們不應該認為新版本是早期描述的替代品。擁有許多不同的表和列表只能加深我們對元素行為方式的理解。