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of nature despite the fact that atomic weights of many common chemical elements show variations as a result of physical chemical and biological processes for more than a century and a half many were taught to use standard atomic weights a single value found on the inside cover of chemistry textbooks and on the periodic table of the elements said ty coplen director of the usgs reston stable isotope laboratory though this change offers significant benefits in the understanding of chemistry one can imagine the challenge now to educators and students who will have to select a single value out of an interval when doing chemistry calculations the standard atomic weights for hydrogen lithium boron carbon nitrogen oxygen silicon sulfur chlorine and thallium previously were expressed as central values with uncertainties that reflected natural atomic weight variations the weights of these elements now will be expressed as intervals to more accurately convey this variation in atomic weight for example boron is commonly known to have a standard atomic weight of 10 811 however its actual atomic weight can be anywhere between 10 806 and 10 821 depending on where the element is found the atomic weight of an element depends upon how many stable isotopes it has and the relative amount of each stable isotope isotopes are atoms of the same element that have different masses variations in atomic weight occur when an element has two or more naturally occurring stable isotopes that vary in abundance modern analytical techniques can measure the atomic weight of many elements precisely and these small variations in an element s atomic weight are important in research and industry for example precise measurements of the abundances of isotopes of carbon can be used to determine purity and source of food products such as vanilla and honey isotopic measurements of nitrogen chlorine and other elements are used for tracing pollutants in streams and groundwater in sports doping investigations performance enhancing testosterone can be identified in the human body because the atomic weight of carbon in natural human testosterone is higher than that in pharmaceutical testosterone elements with only one stable isotope do not exhibit variations in their atomic weights for example the standard atomic weights for fluorine aluminum sodium and gold are constant and their values are known to better than six decimal places the usgs has a long history of research in determining atomic weights of the chemical elements as far back as 1882 frank w clark chief chemist of the usgs prepared a table of atomic weights the year 2011 has been designated as the international year of chemistry the iyc is an official united nations international year proclaimed at the un as a result of the initiative of iupac and unesco iupac will feature the change in the standard atomic weights table as part of associated iyc activities this fundamental change in the presentation of the atomic weights is based upon work between 1985 and 2010 supported by iupac the usgs and other contributing commission members and institutions iupac oversees the evaluation and dissemination of atomic weight values fundamental research underlying the changes in the atomic weight presentation for selected elements is compiled in the report compilation of minimum and maximum isotope ratios of selected elements in naturally occurring terrestrial materials and reagents an abbreviated version of this report is published in the iupac journal pure and applied chemistry vol 74 no 10 pp 1987 2017 2002 doi 10 1351 pac200274101987 an overview of the standard atomic weights through the 20 th century is also available نوشته شده در پنجشنبه ۹ دی ۱۳۸۹ ساعت ۱ ۳ ب ظ توسط س عظیمی جایزه نوبل شیمی 2010 سلام جایزه نوبل شیمی چند دقیقه قبل طی مراسمی در آکادمی علوم سوئیس بطور مشترک اهدا شد به ریچارد ف هک و ای ایچی نگیشی و آکیرا سوزوکی تحقیقات سه شیمیست آلی فوق الذکر در زمینه استفاده از کاتالیزورهای پالادیوم در کراس کوپلینگ واکنشهای جفت شدن کربن کربن بوده است نوشته شده در چهارشنبه ۱۴ مهر ۱۳۸۹ ساعت ۱ ۴۱ ب ظ توسط س عظیمی sci finder a helpful tool for chemists welcome to scifinder work smarter use scifinder with scifinder you can be more productive in your research with convenient easy to use access to the world s scientific information login now use scifinder and work smarter new scifinder features increase research productivity and expand access to substance related patent information new enhancements now available only to researchers using the web version of scifinder will provide powerful new searching capabilities as well as more convenient and time saving features find patent information not previously available to scifinder users related to a chemical structure of interest with explore by markush structure search references by digital object identifiers doi dois are also conveniently displayed in the bibliographic detail for easier reference management and document look up use new highlighting to identify and group reactions with matching transformation centers prioritize answer sets in ascending and descending order sort substance answer sets by molecular formula and molecular weight set a preference to automatically remove medline duplicates stay current with a new monthly frequency keep me posted alert scifinder is on facebook and linkedin want to share search strategies learn about new and existing scifinder features or recommend ways to enhance the scifinder experience visit the new scifinder page on facebook or join the discussion in the new scifinder user group on linkedin cas chemistry research report 40 years of biofuel research reveal china now atop u s in patenting and commercialization of bioethanol the first of a series of reports delivering the latest trends in global chemistry research is now available to learn more visit http www cas org newsevents releases research062410 html scifinder podcasts learn how you can explore a vast array of current interest topics and new discoveries in the 21st century and how scifinder can play a significant role in providing solutions for the advancement of science watch all the podcasts in the scifinder series by visiting the cas media library نوشته شده در سه شنبه ۱۲ مرداد ۱۳۸۹ ساعت ۱ ۳۸ ق ظ توسط س عظیمی عنصر 112 کوپرنیسیوم نامیده شد با علامت شیمیایی cn element 112 is named copernicium iupac has officially approved the name copernicium with symbol cn for the element of atomic number 112 priority for the discovery of this element was assigned in accordance with the agreed criteria to the gesellschaft für schwerionenforschung gsi center for heavy ion research in darmstadt germany the team at gsi proposed the name copernicium which has now been approved by iupac sigurd hofmann leader of the gsi team stated that the intent was to salute an influential scientist who didn t receive any accolades in his own lifetime and highlight the link between astronomy and the field of nuclear chemistry the name proposed by the gesellschaft für schwerionenforschung gsi lies within the long tradition of naming elements to honor famous scientists nicolaus copernicus was born on 19 february 1473 in torún poland and died on 24 may 1543 in frombork frauenburg also in poland his work has been of exceptional influence on the philosophical and political thinking of mankind and on the rise of modern science based on experimental results during his time as a canon of the cathedral in frauenburg copernicus spent many years developing a conclusive model for complex astronomical observations of the movements of the sun moon planets and stars his work published as de revolutionibus orbium coelestium liber sixtus in 1543 had very far reaching consequences indeed the copernican model demanded major changes in the view of the world related to astronomy and physical forces and well as having theological and political consequences the planetary system introduced by copernicus has been applied to other analogous systems in which objects move under the influence of a force directed towards a common centre notably on a microscopic scale this is the bohr model of the atom with its nucleus and orbiting electrons the recommendations will be published in the march issue of the iupac journal pure and applied chemistry and is available online at pure appl chem 2010 vol 82 no 3 pp pp 753 755 doi 10 1351 pac rec 09 08 20 priority of claims to the discovery of the element of atomic number 112 was determined by a joint working party of independent experts drawn from the international union of pure and applied chemistry iupac and the international union of pure and applied physics iupap the group s report was published in july 2009 pure appl chem 2009 vol 81 no 7 pp 1331 1343 doi 10 1351 pac rep 08 03 05 the joint working party will issue a second report dealing with claims for the discovery of elements with atomic numbers in the range 113 to 118 in the near future iupac was formed in 1919 by chemists from industry and academia for more than 90 years the union has succeeded in fostering worldwide communications in the chemical sciences and in uniting academic industrial and public sector chemistry in a common language iupac is recognized as the world authority on chemical nomenclature terminology standardized methods for measurement atomic weights and many other critically evaluated data more information about iupac and its activities is available at www iupac org نوشته شده در سه شنبه ۱۸ اسفند ۱۳۸۸ ساعت ۱ ۱۹ ب ظ توسط س عظیمی درخواست سلام مقاله مروری زیر رو اگر کسی میتونه برام گیر بیاره ممنون میشم و از خجالتش در میام review h weber adv hetrocyclic chem 1987 41 275 نوشته شده در پنجشنبه ۱ بهمن ۱۳۸۸ ساعت ۱۲ ۱۴ ق ظ توسط س عظیمی عناوین و آدرس چند ژورنال رایگان در زمینه شیمی شیمی آلی با امکان دانلود مقالات قانونی سلام اگر شما هم مثل من مشکل همیشگی دسترسی به منابع علمی مقالات بروز در زمینه شیمی آلی دارید فعلا آدرس این چند ژورنال رو داشته باشین که از هر جایی می تونید مقالات رو دانلود کنید البته این ژورنالها در همه زمینه های شیمی است اما بهر حال مطالب مشترک هم درآنها هست ابتدا به سایت ساینس دایرکت بروید و سپس اسم ژورنال رو جستجو کنید و یا اینکه روی اسم آنها کلیک کنید اhttp www sciencedirect com اسامی ژورنال ها عبارتند از arabian journal of chemistry chemistry biology combinatorial chemistry an online journal journal of the american society for mass spectrometry journal of king saud university science procedia chemistry نوشته شده در پنجشنبه ۲ مهر ۱۳۸۸ ساعت ۱ ۵۵ ب ظ توسط س عظیمی اتمهای اکسیژن در اکسید تیتانیوم آکروبات بازی می کنند dancing adatoms help chemists understand how water molecules split sciencedaily mar 16 2009 single oxygen atoms dancing on a metal oxide slab glowing brighter here and dimmer there have helped chemists better understand how water splits into oxygen and hydrogen in the process the scientists have visualized a chemical reaction that had previously only been talked about the new work improves our understanding of the chemistry needed to generate hydrogen fuel from water or to clean contaminated water while exploring titanium dioxide as a way to split water into its hydrogen and oxygen pieces researchers can use a technique called scanning tunneling microscopy to watch the chemical reaction the surface of a slab of titanium dioxide is like a corn field rows of oxygen atoms rise from a patch of titanium atoms the alternating oxygen and titanium rows look like stripes scientists can also see some atoms and molecules that come to rest on the surface as bright spots one such visible atom is a single oxygen atom that comes to rest on a titanium atom called an adatom chemists can only see water molecules if they drop the temperature dramatically at ambient temperature water moves too fast for the method to pick them up in this work pnnl scientists studied water s reactions with titanium dioxide at ambient temperature at emsl the doe s environmental molecular sciences laboratory on the pnnl campus starting with a surface plated with a few oxygen adatoms they added water and the adatoms started to dance suddenly almost every adatom started to move back and forth along the titanium row said lyubinetsky from theory and previous work we expected to see this along the row remarkably the adatoms didn t just slide up and down the stripes they also bounced out of them and landed in others like pogoing dancers in a mosh pit we saw quite unexpected things we thought it was very strange we saw adatoms jump over the rows lyubinetsky said we just couldn t explain it calculating how much energy it would take for the adatoms to move by themselves much less hop over an oxygen row the chemists suspected the adatoms were getting help most likely from the invisible water molecules the unseen enabler to make sense of the dancing adatoms the team calculated how much energy it would take to move adatoms with the help of water molecules if a water molecule sits down next to an adatom one of the water s hydrogen atoms can jump to the adatom forming two oxygen hydrogen pairs these pairs are known as hydroxyls and tend to steal atoms from other molecules including each other one of the thieving hydroxyls can then nab the other s hydrogen atom turning back into a water molecule the water molecule floats off leaving behind an adatom half the time that adatom is one spot over which makes the original appear to have moved the chemists determined that water can help the adatom jump a row as well if a water molecule and an adatom are situated on either side of a raised oxygen row a row oxygen can serve as the middleman handing over a hydrogen from the water molecule to the adatom again two hydroxyls form one ultimately stealing both hydrogens with the help of the middleman and zipping away as water if the incoming water molecule has been stripped the adatom appears to have hopped over the calculated energy required for these different scenarios fit well with the team s experimental data when a row oxygen serves as a middleman the process is known as pseudo dissociation a reaction suggested by chemists but until now never verified experimentally we realized that only if we involved the pseudo dissociative state of the water can we explain it said lyubinetsky otherwise all the calculations show there s too high a barrier the adatom just cannot jump by itself lyubinetsky points out that this shows that water itself can work as a catalyst a catalyst is a molecule that can help a chemical reaction along and remain unchanged by the experience water is required to move the adatoms around but like a catalyst it is not consumed in the reaction he said you start with water and you end with water in the future the team plans on determining if water can make the adatoms move other species and more than one space at a time in addition they will investigate how light affects the reaction this work was supported by the department of energy s office of science نوشته شده در چهارشنبه ۲۸ اسفند ۱۳۸۷ ساعت ۹ ۳۷ ق ظ توسط س عظیمی بررسی مکانیسم واکنشهای آلی 2 با سلام اثر بر...