Sulfur cycle

The sulfur cycle is the collection of processes by which sulfur moves to and from minerals (including the waterways) and living systems. Such biogeochemical cycles are important in geology because they affect many minerals.

Sulfur (S), the tenth most abundant element in the universe, is a brittle, yellow, tasteless, and odorless non-metallic element. It comprises many vitamins, proteins, and hormones that play critical roles in both climate and in the health of various ecosystems. The majority of the Earth’s sulfur is stored underground in rocks and minerals, including as sulfate salts buried deep within ocean sediments.

The sulfur cycle contains both atmospheric and terrestrial processes. Within the terrestrial portion, the cycle begins with the weathering of rocks, releasing the stored sulfur. The sulfur then comes into contact with air where it is converted into sulfate (SO4). The sulfate is taken up by plants and microorganisms and is converted into organic forms; animals then consume these organic forms through foods they eat, thereby moving the sulfur through the food chain. As organisms die and decompose, some of the sulfur is again released as a sulfate and some enters the tissues of microorganisms. There are also a variety of natural sources that emit sulfur directly into the atmosphere, including volcanic eruptions, the breakdown of organic matter in swamps and tidal flats, and the evaporation of water.

Sulfur eventually settles back into the Earth or comes down within rainfall. A continuous loss of sulfur from terrestrial ecosystem runoff occurs through drainage into lakes and streams, and eventually oceans. Sulfur also enters the ocean through fallout from the Earth’s atmosphere. Within the ocean, some sulfur cycles through marine communities, moving through the food chain. A portion of this sulfur is emitted back into the atmosphere from sea spray. The remaining sulfur is lost to the ocean depths, combining with iron to form ferrous sulfide which is responsible for the black color of most marine sediments.

Since the Industrial Revolution, human activities have contributed to the amount of sulfur that enters the atmosphere, primarily through the burning of fossil fuels and the processing of metals. One-third of all sulfur that reaches the atmosphere—including 90% of sulfur dioxide—stems from human activities. Emissions from these activities, along with nitrogen emissions, react with other chemicals in the atmosphere to produce tiny particles of sulfate salts which fall as acid rain, causing a variety of damage to both the natural environment as well as to man-made environments, such as the chemical weathering of buildings. However, as particles and tiny airborne droplets, sulfur also acts as a regulator of global climate. Sulfur dioxide and sulfate aerosols absorb ultraviolet radiation, creating cloud cover that cools cities and may offset global warming caused by the greenhouse effect.

Atom-thin 'borophene' joins 2D materials club

Graphene inspires atom-thin acolyte made from pure boron.

Meet flatland’s latest resident: borophene, a sheet of boron just one atom thick. It joins a family of two-dimensional materials that has been flourishing ever since graphene, the granddaddy of them all, took the world by storm in 2004.

Graphene’s honeycomb arrangement of carbon atoms lends it strength, flexibility and superb electrical conductivity. Borophene’s boron atoms share the same arrangement, but with an extra boron atom cherried on top of each tessellated hexagon. And although borophene has not yet been isolated as a free-standing sheet, there are already tantalizing hints that some of borophene’s properties could surpass those of its flat cousins.
“Borophene is just beginning to be studied,” says Mark Hersam, a materials scientist at Northwestern University in Evanston, Illinois, and part of the team that unveiled the material in Science on 17 December1. “It’s good to get it out there so the field as a whole can take it on — there’s so much to be done with it.”
Earning its stripes
Hersam and his colleagues grew borophene on silver, by evaporating boron atoms from a solid boron rod at temperatures of 450ºC to 700ºC inside an ultrahigh-vacuum chamber. Whereas boron itself is a poor electrical conductor, the team found that borophene is fully metallic. Unprotected samples oxidized in a few hours, but a silicon covering kept them stable for several weeks.
“I was delighted to see this result,” says Deji Akinwande, a nanomaterials researcher at the University of Texas at Austin. “It’s quite different from other 2D materials, which are mostly semiconductors.”
Images under a scanning tunnelling microscope revealed that borophene could take different forms, depending on the temperature used to make it and on how the atoms of boron sat on the silver below. One looked smooth, while the other appeared stripy, with corrugations like the ridges and furrows of a ploughed field.
Calculations suggest that corrugated borophene conducts electricity much better along these ridges than across them; it could even be stiffer and more conductive in this direction than is graphene. Hersam’s team is now trying to measure these qualities experimentally, and he says that their directionality could give borophene an advantage in certain applications, such as a switchable filter for polarized light.
Chemical exuberance
“The next fundamental challenge is to demonstrate a free-standing sheet of this material,” says Akinwande. “That really opens up the science and engineering opportunities.”
Transferring free-standing borophene to an insulating substrate would allow researchers to accurately measure its conductivity, for example. But that’s far from trivial: “Boron reacts with almost everything around it,” says Hermann Sachdev, an inorganic chemist at the Technical University of Kaiserslautern in Germany.
Boron's reactivity may turn out to be an advantage, however, because borophene could be readily modified with other chemical groups or sandwiched between other materials to fine-tune its properties. Boron and many of its compounds are also extremely hard, so if borophene’s chemical exuberance can be controlled it might be easier to handle than more fragile flatlanders such as silicene or germanene (2D sheets of silicon and germanium, respectively). “I expect folks working on silicene may pivot to this,” says Hersam.
Back in February, Akinwande made the first silicene transistor2, and says that he would like to study borophene as well, if he can get the funding. Measurements by Hersam’s team suggest that borophene has a higher electron density than graphene, and Akinwande says that this raises the possibility that cooled borophene could act as a superconductor, carrying electrical charge with no resistance.
Borophene may even point the way to the next 2D material. Aluminium is immediately below boron in the periodic table, and a theoretical study has predicted that it could form atom-thin honeycomb sheets of aluminene3. If that material could be created in the lab, says Akinwande, its conductivity might overshadow both graphene's and borophene's.
Nature doi:10.1038/nature.2015.19060
http://www.nature.com/…/atom-thin-borophene-joins-2d-materi…

History of modern Atomic theory

THE HISTORY OF THE MODERN ATOMIC THEORY

 

400 BC           Democritus                Proposes the idea of the atom

 

1807               John Dalton                Founder of modern atomic theory

                                                            His model survived for almost 100 years

 

1885               J.J. Thomson Discovery of the “proton”

 

1896               Henri Becquerel        Discovery of Radioactivity

 

1897               J.J. Thomson Discovery of the “electron”

 

1903               J.J. Thomson “Plum-pudding” model

 

1909               Ernest Rutherford      The Gold Foil Experiment

 

1911               Ernest Rutherford      Rutherford’s model of the atom

 

1913               Niels Bohr                  Electrons exist in discrete energy levels

 

1923               Robert Millikan          The Oil Drop Experiment

                                                            Discovered the charge of an electron

                                                            Discovered the mass p+ = 1836 the mass of e-

 

1923               Erwin Schrodinger    Wave Particle duality

 

1925               Erwin Schrodigner    Quantum Mechanical Model of the Atom

 

1932               James Chadwick      Discovery of the “neutron”

 

1945               Wolfgang Pauli          Pauli Exclusion Principle

What is Lithium aluminium hydride

Lithium aluminium hydride, commonly abbreviated to LAH, is an inorganic compound with the chemical formula LiAlH4. It was discovered by Finholt, Bond and Schlesinger in 1947. This compound is used as a reducing agent in organic synthesis, especially for the reduction of esters, carboxylic acids, and amides. The solid is dangerously reactive toward water, releasing gaseous hydrogen (H2). Some related derivatives have been discussed for hydrogen storage.

LAH is a colorless solid, but commercial samples are usually gray due to contamination.This material can be purified by recrystallization from diethyl ether. Large-scale purifications employ a Soxhlet extractor. Commonly, the impure gray material is used in synthesis, since the impurities are innocuous and can be easily separated from the organic products. The pure powdered material is pyrophoric, but not its large crystals. Some commercial materials contain mineral oil to inhibit reactions with atmospheric moisture, but more commonly it is packed in moisture-proof plastic sacks.

LAH violently reacts with water, including atmospheric moisture. The reaction proceeds according to the following idealized equation:
  
LiAlH4 + 4 H2O → LiOH + Al(OH)3 + 4 H2

This reaction provides a useful method to generate hydrogen in the laboratory. Aged, air-exposed samples often appear white because they have absorbed enough moisture to generate a mixture of the white compounds lithium hydroxide and aluminium hydroxide.
LAH crystallizes in the monoclinic space group P21/c. The unit cell has the dimensions: a = 4.82, b = 7.81, and c = 7.92 Å, α = γ=90° and β=112°. In the structure, Li+ centers are surrounded by five AlH−4 tetrahedra. The Li+ centers are bonded to one hydrogen atom from each of the surrounding tetrahedra creating a bipyramid arrangement. At high pressures (>2.2 GPa) a phase transition may occur to give β-LAH.
X-ray powder diffraction pattern of as-received LiAlH4. The asterisk designates an impurity, possibly LiCl.
Preparation
LiAH was first prepared from the reaction between lithium hydride (LiH) and aluminium chloride:

4 LiH + AlCl3 → LiAlH4 + 3 LiCl

In addition to this method, the industrial synthesis entails the initial preparation of sodium aluminium hydride from the elements under high pressure and temperature:

Na + Al + 2 H2 → NaAlH4

LiAlH4 is then prepared by a salt metathesis reaction according to:

NaAlH4 + LiCl → LiAlH4 + NaCl

which proceeds in a high yield of LAH. LiCl is removed by filtration from an ethereal solution of LiAH, with subsequent precipitation of LiAH to yield a product containing around 1% w/w LiCl.

Harvard scientists just turned hydrogen into metal

More than 80 years after it was first predicted scientists at Harvard turned hydrogen into metal, and it could revolutionize our planet.

They did it by subjecting hydrogen to extremely high pressures, which changed it from a liquid to a solid.

The resulting material could be used as a superconductor, which would work at room temperature.

This would save lots of energy and money because current superconductors only work at below -269°C.

It could also be used to make MRI scanners and power lines cheaper and more efficient too.

In 1935, scientists predicted that the element hydrogen could become a metal if subjected to enough pressure. Teams have been attempting to confirm the prediction ever since, but have not been able to construct a vise capable of squeezing the element enough without breaking the equipment.

But a team of scientists at Harvard University published a paper this week in the peer-reviewed journal Science saying they managed to squeeze hydrogen in a diamond vise to the point that the element became reflective, a key property of metals.

The study is not merely a parlor trick. Metallic hydrogen is thought to be a superconductor, meaning it could conduct electricity without any resistance. Electricity traveling through normal circuits loses energy to resistance over time, often in the form of heat. This is why it is harder to send electrical currents (say, through the electricity grid) over long distances than short ones. But a current traveling through a superconducting material loses nearly zero energy.

Superconductive metals are used to make the magnets for devices such as hospital MRI machines and particle accelerators such as CERN. The trouble with many superconductors is that the materials now used need to be cooled to extremely low temperatures in order to work, which is expensive.

It is also possible that metallic hydrogen material may be "metastable," according to Science Magazine. This means that, once formed, it may retain its metallic properties even at normal temperatures and pressure levels, like diamonds. If so, it could conduct electricity at nearly 100 percent efficiency in normal conditions. Again, this could dramatically reduce the costs of transferring electrical currents, meaning more powerful and efficient electric motors, and a far more efficient electrical grid.

Scientists have been searching for such a material almost as long as they have known about superconductivity.

Of course, the study has its critics. Eugene Gregoryanz, a physicist at the University of Edinburgh, told Science Magazine he sees a several problems with the experiment's procedures.

"The word garbage cannot really describe it," said Gregoryanz, of the experiment.

The video below, from Harvard, discusses the discovery in detail:

Soft Drink and Processed Food with Sodium benzoate & Leukemia

One of the dirty secrets of the soft drink and processed food industries is sodium benzoate. It is a benzene compound that is produced by mixing benzoic acid with sodium hydroxide. It is a common preservative in processed foods and soft drinks. It has been associated with a vast array of health problems, including all of our major epidemics. Sodium benzoate is considerably more toxic than either processed sugar or high fructose corn syrup, yet it gets very little media coverage. It is a bona fide poison. Outside of our foods, benzene is the main ingredient of Liquid Wrench, various paint stripper products, rubber cement, and spot removers, due to its highly destructive and solvent qualities. It was discontinued in rubber manufacture in the U.S. because it caused a large percentage of workers to get leukemia.

Sodium benzoate is a synthetic chemical produced when benzoic acid, which is found naturally in some fruits and spices, is combined with sodium hydroxide. Since sodium benzoate contains a natural ingredient, it is probably safe, right? After all, the US Food and Drug Administration (FDA) and the Canadian Health Protection Branch have pronounced this chemical preservative to be acceptable when consumed in low amounts.

In fact, the FDA has granted sodium benzoate GRAS (Generally Recognized as Safe) status, and the so-called safe limit in food is 0.1 percent by weight. In water, the acceptable limit, set by the Environmental Protection Agency, is 5 parts per billion (ppb). But this common food additive, which is found in carbonated sodas, fruit juice products, salad dressings, and fermented foods such as vinegar, wine, and pickles, is not natural nor safe. Here’s the story.

Sodium benzoate is a sodium salt that is present at extremely low levels in berries, apples, plums, cinnamon, and several other natural foods. There’s nothing scary about the chemical in these items. But lab-synthesized sodium benzoate (and its close relative, benzoic acid) are a different story. When these preservatives are added to foods and to the interior of metal cans that contain beverages or liquid foods, they can have a detrimental effect on your health.

For example, a small percentage of people are hypersensitive to sodium benzoate and can experience asthmatic attacks, hives, or other allergic reactions when they consume the preservative. A more common problem, however, is the combination of sodium benzoate and citric acid and/or ascorbic acid (vitamin C). When these ingredients get together, they form benzene, a cancer-causing chemical associated with leukemia and other blood cancers.

A comparison of the two principal nucleic acids: RNA (left) and DNA (right)

A comparison of the two principal nucleic acids: RNA (left) and DNA (right), showing the helices and nucleobases each employs.

• Deoxyribonucleic acid (DNA), the genetic material, carries information to specify the amino acid sequences of proteins. It is transcribed into several types of ribonucleic acid (RNA) including messenger RNA (mRNA), transfer RNA (tRNA), and ribosomal RNA (rRNA), which function in protein synthesis.
•  Both DNA and RNA are long, unbranched polymers of nucleotides. Each nucleotide consists of a heterocyclic base linked via a five-carbon sugar (deoxyribose or ribose) to a phosphate group
•  DNA and RNA each contain four different bases. The purines adenine (A) and guanine (G) and the pyrimidine cytosine (C) are present in both DNA and RNA. The pyrimidine thymine (T) present in DNA is replaced by the pyrimidine uracil (U) in RNA.
•  The bases in nucleic acids can interact via hydrogen bonds. The standard Watson-Crick base pairs are G·C, A·T (in DNA), and A·U (in RNA). Base pairing stabilizes the native three-dimensional structures of DNA and RNA.
•  Adjacent nucleotides in a polynucleotide are linked by phosphodiester bonds. The entire strand has a chemical directionality: the 5′ end with a free hydroxyl or phosphate group on the 5′ carbon of the sugar, and the 3′ end with a free hydroxyl group on the 3′ carbon of the sugar . Polynucleotide sequences are always written in the 5′ → 3′ direction (left to right).
•  Natural DNA (B DNA) contains two complementary polynucleotide strands wound together into a regular right-handed double helix with the bases on the inside and the two sugar-phosphate backbones on the outside. Base pairing (A·T and G·C) and hydrophobic interactions between adjacent bases in the same strand stabilize this native structure.
•  Binding of protein to DNA can deform its helical structure, causing local bending or unwinding of the DNA molecule.
•  Heat causes the DNA strands to separate (denature). The melting temperature of DNA increases with the percentage of G·C base pairs. Under suitable conditions, separated complementary nucleic acid strands will renature.
•  Local unwinding of the DNA helix induces stress, which is relieved by twisting of the molecule on itself, forming supercoils. This process is regulated by topoisomerases, which can add or remove supercoils.
•  Natural RNAs are single-stranded polynucleotides that form well-defined secondary and tertiary structures. Some RNAs, called ribozymes, have catalytic activity.

Steps in the hydrogenation of a C=C double bond at a catalyst surface, for example Ni or Pt :

(1) The reactants are adsorbed on the catalyst surface and H2 dissociates.

(2) An H atom bonds to one C atom. The other C atom is still attached to the surface.

(3) A second C atom bonds to an H atom. The molecule leaves the surface.

Advanced Level (A/L) Chemistry new syllabus (Tamil medium, Sri Lankan syllabus) - Mr. M.R. Fahumudeen

A new type of atomic bond has been discovered

An electron corrals a nearby atom closer, creating a supersized molecule – for a fraction of a second
Flitting chemical bond makes giant butterfly molecules
A new type of atomic bond has been discovered
And it forms a whole new class of molecules.
Physicists built a new, supersized molecule made of atoms held together by a far-roaming electron – like a flock of sheep being herded by a sheepdog.
Reporting in Nature Communications, the team from Germany and America created fleeting “butterfly” Rydberg molecules they predicted on paper 14 years ago – and which could find a place in quantum computers.
The new kind of molecule is bound by a lone electron ranging extremely far from its nucleus and whizzing around another atom, herding it close like a sheepdog does a stray sheep.
“It's a whole new way an atom can be bound by another atom," says Chris Greene a physicist at Purdue University, who co-authored the research.
Back in 1888, when most scientists didn’t believe in atoms, Swedish physicist Johannes Rydberg found a formula that reproduced colours of light emitted by different chemical elements.
Some 25 years later, Danish physicist Niels Bohr built on Rydberg’s ideas when he described the ‘solar system’ model of the atom, with the nucleus at the centre orbited by electrons.
One of Bohr’s central ideas was that if you give an electron a kick of energy, you can promote it to a higher energy level, meaning it orbits further, on average, from the nucleus.
Rydberg atoms are extreme examples of this. The outermost electron, promoted to an extremely high energy, can roam up to 1,000 times further from the nucleus than normal.
Rydberg atoms are also atomic monstrosities. They can be up to a millionth of a metre in diameter. That might seem small, but it’s about the size of an Escherichia coli bacterium, which is built from about 90 billion regular atoms.

In 2002, Greene and his team predicted that the free-ranging electron of a Rydberg atom might be used to form a new kind of chemical bond.
They worked out the shape of the atomic orbitals (describing the probability of finding an electron at a particular position around the nucleus) and found it looked like a butterfly – hence the name.
Now they’ve made one.
Since the molecule would be bound by only the “tiniest conceivable” force, Greene knew their only hope using ultracold, almost motionless atoms. His team used rubidium, an element chosen for cold atom experiments because it’s easy to manipulate with lasers.
Greene’s team cooled rubidium gas to just 10 millionths of a degree above absolute zero. Using a laser, they gave an electron a kick of energy, knocking it from its usual orbit out into a super-excited state and creating a Rydberg atom.
They then used the laser again to corral another rubidium atom into just the right distance nearby. That’s when the excited electron took over.
“This electron is like a sheepdog,” says Greene. This herding creates a tiny force of attraction holding the two atoms together in the very fragile butterfly state.
Though the molecule lasted only about five millionths of a second, it was long enough to study.
The butterfly state caused changes in the frequency of light that the Rydberg molecule absorbed. By detecting these changes, the team could measure the energy of binding between the two atoms.
This is not the first kind of Rydberg molecule created. Back in 2007, scientists managed to coax two Rydberg atoms together, each with a herding electron, to form a molecule that looked a little like an extinct marine animal called a trilobite.
The butterfly Rydberg is different because only one atom needs to be in a super-excited state. The other is passively herded.
From a practical point of view, Rydberg molecules have a very high electric dipole moment (in essence, the separation of charge within the molecule) coming from the large distance between the negative electron and positive nucleus.
This means they can be moved around with electric fields 100 times weaker than those needed for regular atoms – useful for setting up the long-range interactions between atoms needed for quantum computing.
For now, Greene plans to see if the ranging electron can herd more than one atom.
https://en.wikipedia.org/wiki/Rydberg_molecule
http://iopscience.iop.org/article/10.1088/0953-4075/…/10/102
http://www.purdue.edu/…/weak-atomic-bond,-theorized-14-year…
http://journals.aps.org/…/ab…/10.1103/PhysRevLett.104.010502
https://en.wikipedia.org/wiki/Rubidium
https://cosmosmagazine.com/…/new-kind-of-chemical-bond-make…
http://www.nature.com/…/jo…/v458/n7241/full/nature07945.html
http://www.nature.com/articles/ncomms12820
http://www.telegraph.co.uk/…/A-giant-molecule-stuns-the-sci…

 

This computer-generated image is of a strange molecule that has shocked chemists. It is as big as a bacterium and should exist in the real world according to research.

Around 200,000,000,000,000,000 conventional atoms would fit on the full stop at the end of this sentence. They are mostly empty space - the positively charged nucleus, where most mass resides, is 100,000 times smaller than the overall atom, which is a mist of negative charge, consisting of one or more electrons.

But the molecule shown here, consisting of only two atoms, is enormous - about one millionth of a metre across, about the same size as an E-coli bacterium.

The predictions that these fragile giants should exist have been published in the Journal of Physics by Edward Hamilton and Prof Chris Greene of the University of Colorado, with Dr Hossein Sadeghpour of the Harvard-Smithsonian Centre for Astrophysics in Cambridge, near Boston.

These are called "butterfly Rydberg states", where butterfly refers to the shape and state refers to the way electrons are distributed around an atom or molecule. Rydberg acknowledges pioneering work in the late 1800s by Johannes Rydberg that helped in the development of quantum mechanics.

This image shows the likelihood of finding an electron in orbit around the molecule (the peaks correspond to where it is most likely to be), calculated by the most successful theory in science, quantum mechanics.

Two years ago, Prof Greene and colleagues, including Prof Alan Dickinson of the University of Newcastle, found a novel and bizarre class of molecular states that involved electron motion that are far more complicated than previously thought. "They showed an uncanny resemblance to a trilobite, and for this reason they were dubbed trilobite states," he said.

Now the team has found a related but different butterfly Rydberg state, which once again is vast compared with conventional atoms and molecules.

Although the practical importance of this work is unclear, the finding has caused a buzz among scientists.

"The main excitement about this work in the atomic and molecular physics community has related to the fact that these huge molecules should exist and be observable, and that their electron density should exhibit amazingly rich, quantum mechanical peaks and valleys," said Prof Greene.

At least one well-known chemist has told Prof Greene that he was shocked by the work because he had thought that everything was known about the simplest molecules that consist of two atoms.

The giant molecules, which are extremely tenuous, have not yet been seen in a laboratory, but a team at the University of Connecticut is now looking for them.

Credit : Vienna University of Technology

Discovery of an extragalactic hot molecular core

Astronomers have discovered a 'hot molecular core', a cocoon of molecules surrounding a newborn massive star, for the first time outside our Galaxy. The discovery, which marks the first important step for observational studies of extragalactic hot molecular cores and challenges the hidden chemical diversity of our universe.

The scientists from Tohoku University, the University of Tokyo, the National Astronomical Observatory of Japan, and the University of Tsukuba, used the Atacama Large Millimeter/submillimeter Array (ALMA) in Chile to observe a newborn star located in the Large Magellanic Cloud, one of the closest neighbors of our Galaxy. As a result, a number of radio emission lines from various molecular gas are detected, which indicates the presence of a hot molecular core associated with the observed newborn star.

The observations have revealed that the hot molecular core in the Large Magellanic Cloud shows significantly different chemical compositions as compared to similar objects in our Galaxy. In particular, the results suggest that simple organic molecules such as methanol are deficient in this galaxy, suggesting a potential difficulty in producing large organic species indispensable for the birth of life.
The research team suggests that the unique galactic environment of the Large Magellanic Cloud affects the formation processes of molecules around a newborn star, and this results in the observed unique chemical compositions.
"This is the first detection of an extragalactic hot molecular core, and it demonstrates the great capability of new generation telescopes to study astrochemical phenomena beyond our Galaxy," said Dr. Takashi Shimonishi, an astronomer at Tohoku University, Japan, and the paper's lead author. "The observations have suggested that the chemical compositions of materials that form stars and planets are much more diverse than we expected. "
It is known that various complex organic molecules, which have a connection to prebiotic molecules formed in space, are detected from hot molecular cores in our Galaxy. It is, however, not yet clear if such large and complex molecules exist in hot molecular cores in other galaxies. The newly discovered hot molecular core is an excellent target for such a study, and further observations of extragalactic hot molecular cores will shed light on the chemical complexities of our universe.
http://iopscience.iop.org/artic…/10.3847/0004-637X/…/72/meta

Cecile G. Tamura