Explaining and how to calculate the relative atomic mass RAM or Ar of an element What is the relative atomic mass of an element? What scale is relative atomic mass based on? What is the formula to work out the relative atomic mass of an element? How to calculate relative atomic mass Introduction Every atom has its own unique relative atomic mass RAM based on a standard comparison or relative scale e. The relative atomic mass scale is now based on an isotope of carbon, namely, carbon , nuclide symbol , which is given the arbitrary value of The unit ‘amu’ is now being replaced by a lower case u, where u is the symbol for the unified atomic mass unit. Since the relative atomic mass of an element is now based on the carbon isotope it can now be defined as Examples are shown in the Periodic Table diagram above. Just scan the periodic table above and examine the pairs of numbers. This has consequences for nuclear stability.
Potassium Element Facts
This toxic compound is formed when powdered osmium is exposed to air, and is a very volatile, water-soluble, pale yellow, crystalline solid with a strong smell. Therefore, osmium powder has a characteristic smell of osmium tetroxide. By contrast, osmium dioxide OsO2 is black, non-volatile, and much less reactive and toxic. Only two osmium compounds have major applications: The lower oxidation states are stabilized by the larger halogens.
Therefore, the trichloride, tribromide, triiodide and even osmium diiodide are known.
Rhenium–Osmium Dating (Meteorites), Figure 2 (a) Isochron diagram for primitive (chondritic) meteorites. Bulk samples of chondrites from the carbonaceous, enstatite, and ordinary chondrite groups are characterized by limited variations in Re/ Os and Os/ Os, compared to most within-group variations for iron meteorites (e.g., Figure 1 above).
Galena would have been noticed by anyone looking for metals in ancient times. Galena generally contains silver, sometimes in significant quantities. Doug Stewart Silver has been in use since prehistoric times. We do not know who discovered it, although the discovery would almost certainly have been of native silver. Nuggets of native silver metal can be found in minerals and sometimes in rivers; but they are rare.
The others were gold , copper , lead and iron. Silver objects dating from before BC have been found in Greece and from slightly later in Anatolia in modern Turkey. Silver artifacts have been found in the Sumerian city of Kish dating from about BC. Galena actually looks metallic see image and would have caught the eyes of people looking for metals. The silver objects found in Greece, Turkey and Kish were made of silver that was refined from lead-containing ores such as galena.
Humans have been successful chemists for a surprisingly long time. First the ore was smelted under reducing conditions to obtain a mixture of silver and lead. The metals then went through cupellation:
Fossils of earliest organisms that had sex are a billion years old Fossils of earliest organisms that had sex are a billion years old A Canadian-led study aims to settle the controversy over extraordinary Arctic fossils that represent the oldest known sexually reproducing organism and the oldest multicellular organism that used photosynthesis. Dec 28, 5: Bangiomorpha pubescens fossils occur in this roughly meter thick rock formation.
The rhenium-osmium (Re-Os) geochronometer is based on the β − decay of radioactive Re to Os with time (decay constant λ = ± × 10 −11 year −1 ; Smoliar et al., ).
Organorhenium chemistry Dirhenium decacarbonyl is the most common entry to organorhenium chemistry. It can be prepared by many routes, a typical method is the reaction of Re2O7 and tetramethyltin: MTO catalyses for the oxidations with hydrogen peroxide. Terminal alkynes yield the corresponding acid or ester, internal alkynes yield diketones, and alkenes give epoxides. MTO also catalyses the conversion of aldehydes and diazoalkanes into an alkene.
Some molybdenum ores contain 0. Rhenium can cause superalloys to become microstructurally unstable, forming undesirable TCP topologically close packed phases. In 4th- and 5th-generation superalloys , ruthenium is used to avoid this effect. Tungsten-rhenium alloys are more ductile at low temperature, allowing them to be more easily machined. The high-temperature stability is also improved. This allows the wire to meet specific performance objectives, including superior vibration resistance, improved ductility, and higher resistivity.
The Universe is ~13.8 Billion Years Old
Survey of the Transition Metals The fact that the transition elements are all metals means that they are lustrous or shiny in appearance, and malleable, meaning that they can be molded into different shapes without breaking. They are excellent conductors of heat and electricity, and tend to form positive ions by losing electrons. Generally speaking, metals are hard, though a few of the transition metals—as well as members of other metal families—are so soft they can be cut with a knife.
Major methods of isotopic dating Uranium–lead method Rubidium–strontium method Samarium–neodymium method Rhenium–osmium method. The decay scheme in which rhenium is transformed to osmium shows promise as a means of studying mantle–crust evolution and the evolution of ore deposits.
Os, and most abundant Os. Alpha decay is predicted for all seven naturally occurring isotopes, but it has been observed only for Os, presumably due to very long half-lives. It is predicted that Os and Os can undergo double beta decay but this radioactivity has not been observed yet. It has also been used to measure the intensity of continental weathering over geologic time and to fix minimum ages for stabilization of the mantle roots of continental cratons.
This decay is a reason why rhenium-rich minerals are abnormally rich in Os. They always observed a small amount of a dark, insoluble residue. After acidification he was able to distill the formed OsO4. Shortly thereafter, in , cheaper catalysts based on iron and iron oxides were introduced by the same group for the first pilot plants, removing the need for the expensive and rare osmium. As with all of the platinum group metals, osmium can be found naturally in alloys with nickel or copper. The largest known primary reserves are in the Bushveld Igneous Complex in South Africa ,  though the large copper—nickel deposits near Norilsk in Russia , and the Sudbury Basin in Canada are also significant sources of osmium.
Smaller reserves can be found in the United States. The second large alluvial deposit was found in the Ural Mountains , Russia, which is still mined.
Origins of photosynthesis in plants dated to 1.25 billion years ago
If we know the number of radioactive parent atoms present when a rock formed and the number present now, we can calculate the age of the rock using the decay constant. The number of parent atoms originally present is simply the number present now plus the number of daughter atoms formed by the decay, both of which are quantities that can be measured.
Samples for dating are selected carefully to avoid those that are altered, contaminated, or disturbed by later heating or chemical events.
The Rhenium-Osmium Dating Method. Versus The Osmium / Method. By Paul Nethercott. May How reliable is radiometric dating? We are repeatedly told that it proves the Earth to be billions of years old. If radiometric dating is reliable than it should not contradict the evolutionary model.
Canadian diamonds found to be oldest on Earth August 22, This is an optical photomicrograph of a sulfide- inclusion-bearing rough diamond from the Jwaneng Mine, Botswana. Below the natural diamond growth surface, at center, is a hexagonal grain of iron sulfide Fe-S surrounded by an irregular black rim. Sulfide grains like these are removed for rhenium-osmium isotopic analysis to reveal the age of the diamond and the composition of the sulfide.
The diameters of these sulfide grains are about microns. Other ancient continents, such as in southern Africa or Siberia, have long been known to have diamonds almost as old, but none that have been so precisely dated. This conclusion documents one of the oldest known examples of modern plate tectonics.
As a first approximation one can assume this, but more accurate results must take into account fluctuations in the intensity of the cosmic rays entering the Earth’s atmosphere. These deviations were determined from the comparative dating of ancient tree rings a field called dendrochronology and the results were then compiled into a calibration curve. For items older than this, there isn’t enough undecayed 14C left to measure the ratio reliably.
The rhenium–osmium ratio in most minerals is too low to be of general use as a dating technique, but molybdenite (molybdenum disulfide, MoS 2) has a very high ratio of rhenium to osmium; and workers have found that the osmium in molybdenite is practically pure radiogenic osmium Ores as old as 3,,, years and as young as 38,, years have been dated this way.
A good example of an application of the Re-Os isochron method is a study on the dating of a gold deposit in the Witwatersrand mining camp, South Africa. Re tends to enter the melt phase incompatible while Os remains in the solid residue compatible. In this regard, the Re—Os system to study the geochemical evolution of mantle rocks and in defining the chronology of mantle differentiation is extremely helpful.
Peridotite xenoliths which are thought to sample the upper mantle sometimes contain supra-chondritic Os-isotopic ratios. This combination of radiogenic Os that was created by decay of Re and nonradiogenic melts helps to support the theory of at least two Os-isotopic reservoirs in the mantle. The second reservoir is chondritic in composition. Direct measurement of the age of continental crust through Re-Os dating is difficult.
Instead, determining model ages can be done in two ways:
Rubidium—strontium method The radioactive decay of rubidium 87Rb to strontium 87Sr was the first widely used dating system that utilized the isochron method. Because rubidium is concentrated in crustal rocks, the continents have a much higher abundance of the daughter isotope strontium compared with the stable isotopes. A ratio for average continental crust of about 0. This difference may appear small, but, considering that modern instruments can make the determination to a few parts in 70, , it is quite significant.
Dissolved strontium in the oceans today has a value of 0.
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Maximizes ability to distinguish between sp2 and sp3 carbon. C KLL acquisition conditions: Interpretation of XPS Spectra The C1s spectrum from a sample with high concentration of sp2 carbon will have a broad, asymmetric tail towards higher binding energy. One or more satellite features, several eV from the main C1s peak, will also be observed in samples with high sp2 concentration. For high concentrations of sp3-bonded carbon, the C1s peak will have a more symmetric shape and will also be slightly shifted to higher binding energy.
Functionalized graphene will have a complex C1s spectrum, containing sp2 and sp3 components. Fit the sp2 component with asymmetric shape preferably derived from a real graphite or graphene sample , including symmetric loss peaks where necessary. The sp3 carbon and functionalized carbon should be fitted with symmetric peak shapes.
The sp3 carbon peak should be 1eV to the higher binding energy side of the sp2 component. Analysis of the X-ray induced C KLL Auger peak can help distinguish these bonding states in a semi-quantitative manner for non-functionalized samples. The differentiated form of the C KLL spectrum allows measurement of the D-parameter, which gives an indication of the relative amounts of sp2 and sp3 carbon.
Measure energy separation between maxima and minima in differentiated C KLL spectrum. For functionalized carbon samples, caution must be exercised if using this method. General Comments Inorganic Carbon e.
How far back can carbon dating date something?
Os, and most abundant Os. Alpha decay is predicted for all seven naturally occurring isotopes, but it has been observed only for Os, presumably due to very long half-lives. It is predicted that Os and Os can undergo double beta decay but this radioactivity has not been observed yet. It has also been used to measure the intensity of continental weathering over geologic time and to fix minimum ages for stabilization of the mantle roots of continental cratons. This decay is a reason why rhenium-rich minerals are abnormally rich in Os.
Rhenium-Osmium dating is a form of radiometric dating based on the beta decay of the isotope Re to Os. This normally occurs with a half-life of × 10 9 y, but studies using fully ionised Re atoms have found that this can decrease to only 33 y.
Davy on the bellows at a public demonstration of science at the Royal Institution in London. Image by James Gillray. Sodium and then potassium reacting with water. Discovery of Potassium Dr. Doug Stewart In English chemist Sir Humphry Davy discovered that chemical bonding was electrical in nature and that he could use electricity to split substances into their basic building blocks — the chemical elements.
In he isolated potassium for the first time at the Royal Institution, London. He electrolyzed dried potassium hydroxide potash which he had very slightly moistened by exposing it to the moist air in his laboratory. The electrolysis was powered by the combined output of three large batteries he had built. He also bravely added potassium to hydrochloric acid and saw it burn with a bright red flame.
Interesting Facts aboutPotassium Potassium and its close periodic table neighbor sodium are solids at room temperature. Their alloys however are not. NaK alloys containing 40 to 90 percent of potassium by weight are liquids at room temperature. All living cells need potassium to maintain fluid balance, therefore we and all other forms of life on Earth need potassium minerals to survive. Potassium is available in all meats, plants and dairy products.
Rhenium Osmium Ntims
Bangiomorpha pubescens fossils occur in this roughly meter thick rock formation. The study, published in the journal Geology, could resolve a long-standing mystery over the age of the fossilized algae, Bangiomorpha pubescens, which were first discovered in rocks in Arctic Canada in The microscopic organism is believed to be the oldest known direct ancestor of modern plants and animals, but its age was only poorly dated, with estimates placing it somewhere between million and 1.
Rhenium-Osmium dating is carried out by the isochron dating method. Isochrons are created by analysing several samples believed to have formed at the same time from a common source. Isochrons are created by analysing several samples believed to have formed at the same time from a .
PDF Abstract More than 40 base metal porphyry ore deposits in southwestern North America are associated with the Laramide orogeny about 90 million to 50 million years ago. Rhenium-osmium dates on molybdenite, a rhenium-enriched sulfide common in many of the deposits, reveal that in individual deposits mineralization occurs near the final stages of magmatic activity irrespective of the time of inception, magnitude, or duration of magmatism. Deposits that differ widely in location and in the extent and timing of magmatism have nearly identical ages for mineralization.
Rhenium-osmium-ages suggest that mineralization occurred during two distinct intervals from about 74 million to 70 million years ago and from 60 million to 55 million years ago. Most deposits that formed in the oldest interval are within the older Precambrian basement of northwestern Arizona, whereas the younger deposits are restricted to the younger Precambrian basement in southern Arizona and northern Mexico.
Synchronous, widespread mineralization indicates that similar crust-mantle interaction occurred on a regional scale for ore deposits once thought to be the product of localized processes.