共查询到19条相似文献,搜索用时 515 毫秒
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张青莲先生的原子量新值测定 总被引:1,自引:0,他引:1
1 九旬豪情再创辉煌 2 0 0 0年 3月 ,人民教育出版社发行的全日制普通高级中学教科书《化学》(第一册 )向全国高中生介绍了我国两位杰出化学家以及他们建树的足以使国人自豪的科学成就。其中之一是我国同位素化学的奠基人、中国科学院资深院士、北京大学化学学院教授张青莲先生。展示的业绩是张青莲先生于 90高龄之际在原子量新值测定方面所取得的举世瞩目的成果。 2 0世纪 90年代初以来 ,张青莲先生主持了一个科研小组 ,实施了测定 1 0项原子量新值的长期计划。现在这项在张先生 82岁高龄时正式启动的研究课题经过历时 1 2年的研… 相似文献
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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。 相似文献
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《科学时报》 《分析测试技术与仪器》2001,7(3):133-133,151
化学元素的原子量是自然科学中的基本常数 ,原子量的概念对化学学科的发展起着基础性的推进作用 .化学发展的两个里程碑 :原子 分子学说和周期率 ,都是以原子量为基础 ,而且一切化学反应、合成、分析以及化学物质的生产 ,都要用原子量计算 .原子量是某元素一个原子的平均质量与一个12 C原子质量的 1/ 12之比 .原子量的测定已有180多年的历史 .测定原子量主要有化学方法和物理方法 (质谱法 ) .现代原子量几乎都是由质谱法测定的 .它是根据公式 :Ar(E) =∑ni=1mifio设元素E含有i种同位素 ,fi 为i同位素的摩尔分数 ,Mi 是其… 相似文献
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硼同位素~(10)B 和~(11)B 由于相对质量差达9.5%,在成矿过程中发生明显的分馏效应,从而导致同位素丰度比 R_(11/10)的变异。最近Holden 对此有详尽的综合评述。国际原子量委员会评估的硼原子量值10.811有较大的不确定度±0.005。本文旨在对若干硼矿物和试剂作精密的 R_(11/10)测量,并以国际硼同位 相似文献
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锂化学试剂中锂同位素丰度及原子量的异常刘卫国,肖应凯,周引民(中国科学院青海盐湖研究所,西宁810008)在1993年第37届国际纯粹与应用化学联会(IUPAC)上,原子量与同位素丰度委员会(CAWIA)根据世界上对锂化学试剂中锂同位素丰度异常的报道... 相似文献
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Ponzevera E Quétel CR Berglund M Taylor PD Evans P Loss RD Fortunato G 《Journal of the American Society for Mass Spectrometry》2006,17(10):1412-1427
A long known way of anchoring isotope ratio values to the SI system is by means of gravimetrically prepared isotopic mixtures. Thermal ionization mass spectrometry (TIMS) is the traditionally associated measurement technique, but multi-collector double focusing inductively coupled plasma (MC-ICP)-MS now appears to be an attractive alternative. This absolute calibration strategy necessitates that mass discrimination effects remain invariant in time and across the range of isotope ratios measured. It is not the case with MC-ICPMS and the present work illustrates, in the case of Zn isotopic measurements carried out using locally produced synthetic Zn isotope mixtures (IRMM-007 series), how this calibration strategy must be adjusted. First, variation in mass discrimination effects across the measurement sequence is propagated as an uncertainty component. Second, linear proportionality during each individual measurement between normalized mass discrimination and the average mass of the isotope ratios is used to evaluate mass discrimination for the ratios involving low abundance isotopes. Third, linear proportionality between mass discrimination and the logarithm of the isotope ratio values for n(67Zn)/n(64Zn) and n(68Zn)/n(64Zn) in the mixtures is used iteratively to evaluate mass discrimination for the same ratios in the isotopically enriched materials. Fourth, ratios in natural-like materials (including IRMM-3702 and IRMM-651) are calibrated by external bracketing using the isotopic mixtures. The relative expanded uncertainty (k = 2) estimated for n(68Zn)/n(64Zn) and n(67Zn)/n(64Zn) ratio values in the synthetic isotopic mixtures and the natural-like zinc samples was in the range of 0.034 to 0.048%. The uncertainty on the weighing (0.01%, k = 1) was the largest contributor to these budgets. The agreement between these results and those obtained with a single detector TIMS and with another MC-ICPMS further validated this work. The absolute isotope ratio values found for IRMM-3702-material also proposed as "delta 0" for delta-scale isotopic measurements-are n(66Zn)/n(64Zn) = 0.56397 (30), n(67Zn)/n(64Zn) = 0.082166 (35), n(68Zn)/n(64Zn) = 0.37519 (16), and n(70Zn)/n(64Zn) = 0.012418 (23). The derived Zn atomic weight value Ar(Zn) = 65.37777 (22) differs significantly from the current IUPAC value by Chang et al. [1]. Remeasurement, with isotopic mixtures from the IRMM-007 series, of the Zn isotope ratios in the same Chang et al. [1] material have revealed large systematic differences (1.35 (27)% per atomic mass unit) that suggest unrecognized measurement biases in their results. 相似文献
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A speed dependent modified Voigt function (MVF) is utilized to describe atomic spectral line profiles and compared to the well known Voigt function (VF). The air—acetylene flame has been used for these comparisons. In all cases the MVF differs from the VF in the calculation of atomic absorption coefficients (up to 15%), full-width half-maximum (FWHM) intensity values (up to 18%), and a-parameter values (up to 80%). The variation between the functions is mass dependent and decreases with atomic weight. The MVF is used to evaluate published lineshape data and reveals a significant difference in calculated collisional cross section values. In addition an experimental situation is evaluated using the MVF and VF to show that the perturber gas in a graphite furnace is important due to its influence on the absorption coefficient at line center. 相似文献
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Even before the 20th century, a consistent set of internationally accepted atomic weights was an important objective of the scientific community because of the fundamental importance of these values to science, technology and trade. As the 20th century progressed, physicists, geoscientists, and metrologists collaborated with chemists to revolutionize the science of atomic weights. At the beginning of the century, atomic weights were determined from mass relationships between chemical reactants and products of known stoichiometry. They are now derived from the measured isotopic composition of elements and the atomic masses of the isotopes. Accuracy in measuring atomic weights has improved continually, leading to the revelation of small but significant variations in the isotope abundances of many elements in their normal terrestrial occurrences caused by radioactivity and a variety of physicochemical and biochemical fractionation mechanisms. This atomic-weight variability has now been recognized as providing new scientific insights into and knowledge of the history of materials. Atomic weights, except those of the monoisotopic elements, are thus no longer regarded as "constants of nature". At the beginning of the 20th century, two scales for atomic weights were in common use: that based on the atomic weight of hydrogen being 1 and that based on the atomic weight of oxygen being 16. Atomic weights are now scaled to (12)C, which has the value 12 exactly. Accurate atomic weights of silicon, silver, and argon, have enabled the values of the Avogadro, Faraday and Universal Gas constants, respectively, to be established, with consequent effects on other fundamental constants. 相似文献
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Covalent radii revisited 总被引:1,自引:0,他引:1
Cordero B Gómez V Platero-Prats AE Revés M Echeverría J Cremades E Barragán F Alvarez S 《Dalton transactions (Cambridge, England : 2003)》2008,(21):2832-2838
A new set of covalent atomic radii has been deduced from crystallographic data for most of the elements with atomic numbers up to 96. The proposed radii show a well behaved periodic dependence that allows us to interpolate a few radii for elements for which structural data is lacking, notably the noble gases. The proposed set of radii therefore fills most of the gaps and solves some inconsistencies in currently used covalent radii. The transition metal and lanthanide contractions as well as the differences in covalent atomic radii between low spin and high spin configurations in transition metals are illustrated by the proposed radii set. 相似文献
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The criterion of orientating group of electrophilic aromatic nitration was discussed by means of pattern recognition method with quantum-chemical parameters as features, and the product ratios of the reactions were quantitatively calculated using artificial neural network (ANN) method with the same parameters as inputs, based on the ab initio calculation of quantum chemistry. The quantum-chemical parameters involved orbital energy, orbital electron population, atomic total electron density and atomic net charge. The predicted values are in agreement with experimental results and (he predicted error of the ANN with quantum-chemical parameters for the reaction is the smallest among the all methods. 相似文献
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L. A. Farias D. I. T. Favaro V. A. Maihara Vasconcellos M. B. A. L. K. Yuyama J. P. L. Aguiar F. J. Alencar 《Journal of Radioanalytical and Nuclear Chemistry》2006,270(1):217-223
Summary Daily dietary intake of Hg and some essential elements in diets of children from communities in the Jaú National Park, Amazon
region, were assessed. Diet samples were analyzed for total Hg content using cold vapor atomic absorption spectrometry and
Ca, Fe, K, Na, Se and Zn contents by instrumental neutron activation analysis. The weekly tolerable provisional intake for
Hg in the communities studied varied from 13 to 57 mg of Hg per kg of body weight, exceeding the limit of 5 mg . kg-1 set by the WHO. Comparison of the daily dietary intake values to the new Dietary Reference Intakes (4-8 years), showed prevalence
of inadequacy. 相似文献
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Hanai T 《Journal of chromatography. A》2003,985(1-2):343-349
Retention times of phenolic compounds in a given pH eluent in reversed-phase liquid chromatography were predicted from dissociation constants derived from atomic partial charges and log P-values calculated by a computational chemical method. The precision of the calculation of atomic partial charges by AMI and PM3 methods of MOPAC was evaluated. The atomic partial charges obtained by AMI were the more acceptable. The atomic partial charges obtained from the hydrogen of the hydroxyl group included an ortho-effect, therefore an ortho-effect was added to the predicted values. The precision of predicted retention factors obtained using predicted pKa values was similar to that using reference pKa values. 相似文献