原子量之"变"

原子量是最为基础的科学概念之一,"国际纯粹与应用化学联合会(IUPAC)"之"同位素丰度和原子量委员会(CIAAW)"每两年会修订并发布一次原子量。自2009年起,IUPAC宣布某些元素的原子量不再是常数,这些元素的标准原子量为区间值。为方便使用,对于这些元素,给出一个合理的单一数值,称为常规原子量。何为标准原子量?何为常规原子量?为何某些元素的原子量出现区间值?依据原子量数值的特性,元素可以分为几大类?本文在介绍最新元素周期表中原子量的特点之后,简述原子量测定、标准确定、概念演变的发展历史,讨论原子量的修订与变化等问题。     

Atomic weights and isotopic abundances of the elements: A future concern for the analytical chemist

Summary The recent evolution and present status of the atomic weights of the elements is reviewed. Attention is drawn upon a number of rather unknown characteristics of these values: the accuracy of a considerable number of atomic weights has been decreased due to lack of justification of the number of significant figures in published values. Furthermore geological and artificial variations in isotopic composition start to influence atomic weights of some elements being circulated in the reagents market; the analytical chemist should be aware of it.The concept of atomic weights and natural isotopic abundances being fundamental constants of nature should be abandoned.

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Atomgewichte und Isotopenhäufigkeiten der Elemente: ein künftiges Problem für den Analytiker

Zusammenfassung Ein Überblick wird gegeben über die jüngste Entwicklung und den gegenwärtigen Stand. Auf eine Anzahl ziemlich unbekannter Charakteristica dieser Daten wird hingewiesen. So hat z.B. die Genauigkeit vieler Atomgewichte abgenommen, da die Angabe der in den Veröffentlichungen angegebenen Dezimalstellen nicht mehr gerechtfertigt ist. Außerdem beginnen geologische und künstliche Veränderungen in der Isotopenzusammensetzung die Atomgewichte einiger Elemente, die in Reagentien verwendet werden, zu beeinflussen. Der Analytiker sollte darauf achten. Die Vorstellung von Atomgewichten und natürlichen Isotopenhäufigkeiten als grundlegenden Naturkonstanten sollte aufgegeben werden.

Associate Member of the IUPAC International Commission on Atomic Weights.     

Certified reference materials in analytical chemistry – A century of NIST contribution

Over the course of its first 100 years, the National Institute of Standards and Technology (NIST) has made numerous contributions to advancing the science and practice of analytical chemistry. Contributions to fundamental constants and reference data, such as determination of the Faraday, Avagadro’s number, and atomic masses, began at almost the beginning of the new institution when it was formed in 1901. Instrumentation development, improvement, and reproducible methods for its use have also been an important part of the NIST effort. This paper will describe what may be the organization’s most important and certainly its most unique contribution; namely, certified reference materials. Ultimately these certified reference materials would become known at NIST as standard reference materials (SRMs). It is a contribution that now has been mirrored around the world with reference materials being certified in at least 25 countries and routinely applied in more than twice that number. The result has been more accurate analyses of materials that impact our safety, health, and well-being. Received: 22 November 2000 Accepted: 22 November 2000     

分析化学的第二个春天

从研究分析化学的历史发展入手，以大量历史事实为根据，指出分析化学曾经历过两次重大变革。第一次变革(19世纪末至20世纪初)使分析化学从分析化学家的技艺发展为科学；第二次变革(20世纪70年代迄今)则使分析化学进入了分析化学家重新当家作主的、欣欣向荣的“第二个春天”。     

磷单质概念的新发展

自白磷与红磷相继被发现后，磷单质的概念初步形成。20世纪初期，黑磷的发现突破了人们对磷单质的认识。随后，紫磷、蓝磷、二磷分子以及环状磷的出现，使磷单质的概念有了新的发展。几种新的磷单质的发现，建立了磷单质概念的新范式，科学家在探索磷单质概念多元化的道路上还将继续前行。     

About the dependence of the intensity of X-ray spectra of elements on their concentrations expressed in atomic and mass percents

The consideration of the classical physical fundamentals of X-ray spectrometry suggests that the properties of X-ray spectra of elements are determined by their atomic number rather than atomic weight. The intensity of X-ray spectra is determined by the number of excited atoms rather by their mass. However, in the middle of the 20th century, the dependence of intensity on the mass concentration of elements was introduced without any physical grounds. The paper presents physical, analytical, and metrological evidences for the idea that this dependence does not correspond to a real physical process. It results in distorted calibration characteristics and extra errors and hinders the development of a method of universal (for all element systems) quantitative X-ray fluorescence analysis instead of specific procedures with empirical parameters for each particular system. The dependence on atomic concentrations eliminates these difficulties.     

The atomic number revolution in chemistry: a Kuhnian analysis

This paper argues that the field of chemistry underwent a significant change of theory in the early twentieth century, when atomic number replaced atomic weight as the principle for ordering and identifying the chemical elements. It is a classic case of a Kuhnian revolution. In the process of addressing anomalies, chemists who were trained to see elements as defined by their atomic weight discovered that their theoretical assumptions were impediments to understanding the chemical world. The only way to normalize the anomalies was to introduce new concepts, and a new conceptual understanding of what it is to be an element. In the process of making these changes, a new scientific lexicon emerged, one that took atomic number to be the defining feature of a chemical element.     

Von Seefahrern,Meerschweinchen und Citrusfrüchten. Der lange Kampf gegen Skorbut

Although scurvy has been around since the beginning of mankind, it was not until the 16th century that it was recognized as a disease. It took hundreds of years and a long sequence of small advances and missed opportunities to discover its cause. Finally at the beginning of the 20th century and with the help of guinea pigs for testing the experiments, scurvy was identified as a form of malnutrition. This started an exciting race for the isolation, structure determination, and synthesis of vitamin C. As a result, modern industrial synthesis now allows an affordable Vitamin C supply for everyone. This success story due to modern chemistry has made scurvy one of the many diseases that have almost entirely disappeared from our lives.     

张青莲教授及其原子量新值测定研究

张青莲教授是中国科学院院士,我国同位素化学的奠基人.本文介绍他在90高龄之际在原子量新值测定方面所取得的杰出成就.从1990年代初以来,他主持一个科研小组采用质谱法,实施了测定10项原子量新值的长期计划.至2001年7月已经有In、Ir、Sb、Eu、Ce、Er、Ge、Dy和Zn等9个原子量新值被国际纯粹与应用化学联合会(IUPAC)的原子量与同位素丰度委员会(CAWIA)正式确定为原子量的国际新标准;另外一个Sm原子量新值也于2005年被国际组织确认.     

Alfred Nier and the sector field mass spectrometer

Science and technology are intimately related, and advances in science often become possible with the availability of new instrumentation. This has certainly been the case in mass spectrometry, which is used in so many scientific disciplines. Originally developed as an instrument for research in physics it was used in the discovery of isotopes, their recognition as the fundamental species comprising the elements, and the investigation of elemental isotopic composition. Isotope ratio mass spectrometry is a metrological technique of the highest order, and has been widely used in chemical, biochemical, cosmochemical, environmental, geological, physical, and nuclear research. Mass spectrometry presently plays a key role not only in scientific research, but also in industrial operations. This paper highlights the role that Alfred Otto Carl Nier played in bringing mass spectrometry into the mainstream of science. Nier's career spanned a remarkable period in science, and he made crucial contributions to atomic weights, geochronology, isotope geochemistry, nuclear physics, and space science. He is widely viewed as the 'father of modern mass spectrometry', because of his genius with instrumentation, his innovations, and the generosity with which he shared his ideas and designs. It is timely to remember his fundamental work in mass spectrometry, particularly the development of the sector field mass spectrometer, which is still the instrument of choice for many isotope scientists some 66 years after its first appearance in 1940.     

C60 and carbon: a postbuckminsterfullerene perspective

The discovery of the fullerenes and nanotubes has completely changed our perspective on various aspects of carbon chemistry and materials science in quite fundamental ways. The experiments, which uncovered C₆₀, occurred between 1985 and 1990 and there are lessons to be learned of various kinds over the way scientific advances occur and more importantly the way misconceptions can propagate. For instance much of our received wisdom over the behaviour of carbon, in particular graphite on a microscopic scale, was really quite ill-conceived and certainly misleading. Questions might be asked as to why it took almost till the end of the 20th century for the fact to be uncovered that the elegant C₆₀ molecule had been lurking in the dark shadows of soot chemistry all the time. After all, mass spectrometric techniques were sufficiently advanced for the discovery to have been made in the 1960’s—perhaps even earlier. Some of these issues are addressed here and the discussion gives an insight into the curiously unpredictable way fundamental scientific advances sometimes occur and also highlights the limitations of applied research in this case.     

Reading Polymers: Sequencing of Natural and Synthetic Macromolecules

The sequencing of biopolymers such as proteins and DNA is among the most significant scientific achievements of the 20th century. Indeed, modern chemical methods for sequence analysis allow reading and understanding the codes of life. Thus, sequencing methods currently play a major role in applications as diverse as genomics, gene therapy, biotechnology, and data storage. However, in terms of fundamental science, sequencing is not really a question of molecular biology but rather a more general topic in macromolecular chemistry. Broadly speaking, it can be defined as the analysis of comonomer sequences in copolymers. However, relatively different approaches have been used in the past to study monomer sequences in biological and manmade polymers. Yet, these “cultural” differences are slowly fading away with the recent development of synthetic sequence‐controlled polymers. In this context, the aim of this Minireview is to present an overview of the tools that are currently available for sequence analysis in macromolecular science.     

Ionic Fluorescence Spectrometry of Rare Earth and Alkaline Earth Elements Using High Current Microsecond Pulsed Hollow Cathode Lamps As Excitation Sources and Inductively Coupled Plasma with a Conventional “Short” Torch as an Atomization Cell

Atomic fluorescence spectrometry (AFS) minimizes spectral overlap interference, often occurring in atomic emission spectrometry especially for such elements as rare earth elements (REEs). It has broader linear dynamic range than atomic absorption spectrometry, and is potentially a multi-element technique.     

The Table of Standard Atomic Weights—An exercise in consensus

The present Table of Standard Atomic Weights (TSAW) of the elements is perhaps one of the most familiar data sets in science. Unlike most parameters in physical science whose values and uncertainties are evaluated using the “Guide to the Expression of Uncertainty in Measurement” (GUM), the majority of standard atomic-weight values and their uncertainties are consensus values, not GUM-evaluated values. The Commission on Isotopic Abundances and Atomic Weights of the International Union of Pure and Applied Chemistry (IUPAC) regularly evaluates the literature for new isotopic-abundance measurements that can lead to revised standard atomic-weight values, A_r°(E) for element E. The Commission strives to provide utmost clarity in products it disseminates, namely the TSAW and the Table of Isotopic Compositions of the Elements (TICE). In 2016, the Commission recognized that a guideline recommending the expression of uncertainty listed in parentheses following the standard atomic-weight value, for example, A_r°(Se) = 78.971(8), did not agree with the GUM, which suggests that this parenthetic notation be reserved to express standard uncertainty, not the expanded uncertainty used in the TSAW and TICE. In 2017, to eliminate this noncompliance with the GUM, a new format was adopted in which the uncertainty value is specified by the “±” symbol, for example, A_r°(Se) = 78.971 ± 0.008. To clarify the definition of uncertainty, a new footnote has been added to the TSAW. This footnote emphasizes that an atomic-weight uncertainty is a consensus (decisional) uncertainty. Not only has the Commission shielded users of the TSAW and TICE from unreliable measurements that appear in the literature as a result of unduly small uncertainties, but the aim of IUPAC has been fulfilled by which any scientist, taking any natural sample from commerce or research, can expect the sample atomic weight to lie within A_r°(E) ± its uncertainty almost all of the time.     

An inertial model of atoms: atomic spectra as a resonance problem

A new model of atoms based on the theory of material waves is proposed. Atoms are characterized by an inertial aggregation of negative charge within the atomic shell, the calculation yields, for hydrogen atoms, an atomic radius of 0.470 nm. Atomic spectra result from radial material waves, quantization being the consequence of boundary conditions imposed on the fundamental wave equation. Stark effects and Zeeman effects are treated in detail, they are referred to deformations and rotations of the atomic shell. An analysis of Stern--Gerlach experiments bases subsequent deflections of single atoms on rotations and interactions of magnetic fields.     

Would Introductory Chemistry Courses Work Better with a New Philosophical Basis?

One of the main functions that introductory chemistry courses havefulfilled during the past century has been to provide evidence for the generalvalidity of 'the atomic hypothesis.' A second function has been to demonstratethat an analytical approach has wide applicability in rationalizing many kindsof phenomena. Following R.G. Collingwood, these two functions can be recognizedas related to a philosophical 'cosmology' (worldview, weltanshauung) thatbecame dominant in the late Renaissance. Recent developments in many areasof science, and in chemistry, have emphasized the central importance of understandingsynthetic, developmental, and evolutionary aspects of nature. This paperargues that these scientific developments, and changes in other aspects of culture,amount to a widespread shift to an alternative cosmology, a quite different generalworldview. To the extent that this is the case, introductory chemistry coursesought to be changed in fundamental ways. Rather than having a main focus onanalysis to microscopic components, introductory chemistry instruction shouldemphasize current scientific understanding of the (synthetic) evolutionary originsof the present world. This altered approach would provide good preparation forfuture professional work, while also making better contact with the perceivedconcerns of students.     

Evaluation of the odd-even effect in limits of detection for electron microprobe analysis of natural minerals

Limit of detection (LOD), being a fundamental quality parameter for analytical techniques, has been recently investigated and a systematic behavior has been observed for most odd-even element pairs for many techniques. However, to the best of our knowledge very few LOD data are available in published literature for electron microprobe analysis; these consist of three papers, two being on rare-earth elements and the third covering a large number of elements of atomic number between 21 and 92. These data confirm the systematic behavior of LODs for many odd-even pairs. To initiate to full this gap, we determined LODs for several major rock-forming chemical elements from Na to Fe with atomic numbers between 11 and 26, during the microprobe analysis of common minerals (olivine, plagioclase, pyroxene, amphibole, quartz, and opaques) in volcanic rocks. The odd-even effect of nuclear stability seems to be present in LOD data for most odd-even pairs investigated. Nevertheless, the experimental strategy concerning the reference materials, calibration procedure, and blank measurements, should be substantially modified to better evaluate the systematic behavior of LOD values in microprobe analysis.     

氩元素概念的形成和发展与化学思想的演进

19世纪末英国化学家瑞利和拉姆塞发现了氩元素,开启了发现稀有气体元素的历程,开辟了发现元素周期表中的零族元素之门。20世纪20年代氩元素同位素的发现使人们形成了对氩元素的概念的现代认知,同时英国化学家莫斯莱提出原子序数概念,揭示了元素在周期表中位置排列的实质,同氩同位素的发现相结合,解决了氩在周期表中的位置排列问题。20世纪上半叶原子结构和化学键理论的提出阻碍了氩化合物的发现。21世纪初,氟氩化氢的发现使人们对氩的“惰性”有了全新的认识,改称氩为稀有气体元素,并对化学键理论的发展起到促进作用。总之,氩元素概念的形成和发展对于元素周期律的完善和发展以及人们对原子结构和化学键理论的认识都起到了极为重要的桥梁作用。