Arsenic

Arsenic is a chemical element with symbol As and atomic number 33. Arsenic occurs in many minerals, usually in conjunction with sulphur and metals, and also as a pure elemental crystal. Arsenic is a metalloid. It can exist in various allotropes, although only the grey form has important use in industry.

 

Arsenic atoms can assume several different bonding patterns which are the basis of its allotropes, each of which has a different colour; metallic grey, yellow and black arsenic. Interestingly, using a hammer to bang on arsenide minerals releases a garlic-like odour, which is the result of toxic fumes created by the oxidation of arsenic to arsenic trioxide.

Arsenic is notoriously poisonous to multicellular life, although a few species of bacteria are able to use arsenic compounds as respiratory metabolites. Arsenic contamination of groundwater is a problem that affects millions of people across the world.

Historically, Arsenic was commonly used as a rodent poison in English households, and it was also a convenient murder weapon, particularly amongst the ruling classes as you may have read in various novels and non-fiction books. However, Victorian England used arsenic in a number of ways; it was incorporated into wallpaper to prevent the growth of mould during the dark, damp English winters, it was used as the green colouring in paints, candies and candles, and as a preservative in lace.

The main use of metallic arsenic is for alloying with lead. Lead components in car batteries are strengthened by the presence of a very small percentage of arsenic.

Widespread arsenic contamination of groundwater has led to a massive epidemic of arsenic poisoning in Bangladesh and neighbouring countries. It is estimated that approximately 57 million people in the Bengal basin are drinking groundwater with arsenic concentrations elevated above the World Health Organization's standard of 10 parts per billion (ppb).

More recently arsenic has been in the news for being found in rice.  Rice holds higher levels of arsenic than other grains and acts as one of nature’s “great scavengers of metallic compounds.” Unlike, millet or polenta, rice planted in arsenic-contaminated fields acts as a vacuum for the toxin.

Rice from different countries contain differing levels of arsenic.  It's recommended that rice is washed before cooking and rinsed afterwards to lessen the effects.

Currently, the FDA in America doesn't have safety levels for arsenic in rice. They've cautioned against making state-by-state or country-by country comparisons in Inorganic Arsenic levels for rice, citing the varying factors that can influence arsenic concentrations, such as soil composition, fertilizers, seasonal variability, and water-use practices.

Evidence-based public health advocates also recommend that, given the lack of regulation or labelling for arsenic in the U.S., children should eat no more than 1 to 1.5 servings per week of rice and should not drink rice milk as part of their daily diet before age 5. They also offer recommendations for adults and infants on how to limit arsenic exposure from rice, drinking water, and fruit juice.

A 2014 World Health Organization advisory conference will consider limits of 200–300 ppb for rice.  The proposed new EU recommendations will limit 200 parts of arsenic per billion for adults and just 100 ppb for children and babies.

For more information visit:-
http://en.wikipedia.org/wiki/Arsenic
http://www.theguardian.com/science/punctuated-equilibrium/2011/oct/14/1
https://time.com/3592399/arsenic-rice/
http://www.dailymail.co.uk/news/article-2817542/More-half-rice-products-exceed-new-EU-limits-ARSENIC.html

On this day - Marie Curie

Marie Curie was a Polish-born physicist and chemist and one of the most famous scientists of her time. Together with her husband Pierre, she was awarded the Nobel Prize in 1903, and she went on to win another in 1911.

Marie Sklodowska was born in Warsaw on 7 November 1867, the daughter of a teacher. In 1891, she went to Paris to study physics and mathematics at the Sorbonne where she met Pierre Curie, professor of the School of Physics. They were married in 1895.

She developed a theory of radioactivity (a term that she coined) and techniques for isolating radioactive isotopes.  She also discovered two elements, polonium and radium. Under her direction, the world's first studies were conducted into the treatment of neoplasms, using radioactive isotopes. She founded the Curie Institutes in Paris and in Warsaw, which remain major centres of medical research today.

During World War I, she established the first military field radiological centres.  After a quick study of radiology, anatomy, and automotive mechanics she procured X-ray equipment, vehicles, auxiliary generators, and developed mobile radiography units, which came to be popularly known as petites Curies ("Little Curies").  She became the director of the Red Cross Radiology Service and set up France's first military radiology centre, operational by late 1914.

Marie and her husband worked together investigating radioactivity, building on the work of the German physicist Roentgen and the French physicist Becquerel. In July 1898, the Curies announced the discovery of a new chemical element, polonium. At the end of the year, they announced the discovery of another, radium. The Curies, along with Becquerel, were awarded the Nobel Prize for Physics in 1903.

Marie received a second Nobel Prize, for Chemistry, in 1911.

Curie died in 1934 due to aplastic anaemia brought on by exposure to radiation – including carrying test tubes of radium in her pockets during research (she also stored them in her desk drawer, remarking on the faint light that the substances gave off in the dark) and her World War I service in mobile X-ray units created by her.  She was exposed to X-rays from unshielded equipment.

Marie and Pierre Curie experimenting with radium, a drawing by André Castaigne

Because of their levels of radioactivity, her papers from the 1890s are considered too dangerous to handle.  Even her cookbook is highly radioactive.  Her papers are kept in lead-lined boxes, and those who wish to consult them must wear protective clothing.

For more information visit:-
http://en.wikipedia.org/wiki/Marie_Curie
http://www.bbc.co.uk/history/historic_figures/curie_marie.shtml
http://prlabpak.blogspot.co.uk/2013/09/radium.html

 

Zinc

Zinc is a metallic chemical element; it has the symbol Zn and atomic number 30. It is the first element of group 12 of the periodic table. It’s the 24th most abundant element in the Earth's crust and has five stable isotopes. The most common zinc ore is sphalerite (zinc blende), a zinc sulfide mineral. The largest mineable amounts are found in Australia, Asia, and the United States.

Brass, which is an alloy of copper and zinc, has been used since at least the 10th century BC.

Zinc is an essential mineral of "exceptional biologic and public health importance".  Zinc deficiency affects about two billion people in the developing world and is associated with many diseases.  In children it causes growth retardation, delayed sexual maturation, infection susceptibility, and diarrhoea, contributing to the death of about 800,000 children worldwide per year.

The metal is most commonly used as an anti-corrosion agent.  Galvanization, which is the coating of iron or steel to protect the metals against corrosion, is the most familiar form of using zinc in this way.  Zinc is more reactive than iron or steel and thus will attract almost all local oxidation until it completely corrodes away.  A protective surface layer of oxide and carbonate forms as the zinc corrodes.  This protection lasts even after the zinc layer is scratched but degrades through time as the zinc corrodes away.  The zinc is applied electrochemically or as molten zinc by hot-dip galvanizing or spraying. Galvanization is used on chain-link fencing, guard rails, suspension bridges, light posts, metal roofs, heat exchangers, and car bodies.

Zinc Oxide used in paint pigments

Zinc is useful for the human body and helps speed up the healing process after an injury.  It is also suspected of being beneficial to the body's immune system. Indeed, zinc deficiency may have effects on virtually all parts of the human immune system.

For more information visit:-

http://www.theguardian.com/science/punctuated-equilibrium/2011/sep/23/1?guni=Article:in%20body%20link

http://en.wikipedia.org/wiki/Zinc

Mercury

Mercury is a chemical element with the symbol Hg and atomic number 80. It is commonly known as quicksilver and was formerly named hydrargyrum (from Greek "hydr-" water and "argyros" silver)

 

 

Mercury is remarkable because it is the only metal that is liquid at room temperature. It is a dense, lustrous grey metal. Mercury is extremely rare in the Earth's crust and in the wild, it typically is concentrated near volcanically active areas, either as the pure metal or in a number of minerals.

 

Mercury is used in thermometers, barometers, manometers, sphygmomanometers, float valves, mercury switches, mercury relays, fluorescent lamps and other devices, though concerns about the element's toxicity have led to mercury thermometers and sphygmomanometers being largely phased out in clinical environments in favour of alternatives such as alcohol- or galinstan-filled glass thermometers and thermistor- or infrared-based electronic instruments.

The reason mercury was so popular is because it readily forms stable amalgams with a number of other metals, particularly silver and gold, making them workable at lower temperatures, and these amalgams have been the source of many instances of mercury poisoning.

Amalgam Filling

 

Biologists are quite interested in mercury because it is highly toxic to life, causing both acute and chronic poisoning. Mercury can be absorbed through the skin and mucous membranes and mercury vapors can be inhaled. Mercury is concentrated in the body over the lifetime of the individual, and it also becomes more concentrated when one animal eats another, which is how it moves up the food chain. This is the reason why the flesh of tuna, a long-lived apex predator in the oceans, contain such high levels of mercury.

For more information visit:-

http://www.theguardian.com/science/grrlscientist/2013/jan/25/1?guni=Article:in%20body%20link

http://en.wikipedia.org/wiki/Mercury_(element)



Magnesium

Magnesium has the atomic number 12 and is an alkaline earth metal with the symbol Mg. It is a common element, the eighth-most-abundant element in the Earth's crust and ninth in the known universe as a whole. Magnesium is the fourth-most-common element in the Earth as a whole (behind iron, oxygen and silicon), making up 13% of the planet's mass and a large fraction of the planet's mantle.

The free element (metal) is not found naturally on Earth, as it is highly reactive (though once produced, it is coated in a thin layer of oxide (see passivation), which partly masks this reactivity). The free metal burns with a characteristic brilliant-white light, making it a useful ingredient in flares. You probably remember burning Magnesium Ribbon in school.  Some of the light that burning magnesium produces is in the ultraviolet range. Just as ultraviolet light will burn your skin, it will also burn the retinas of your eyes if they are not protected, hence not looking directly at the light or using suitable safety eyewear.

Since magnesium is less dense than aluminium, these alloys are prized for their relative lightness and strength.

Magnesium has many uses, but most of us are familiar with aluminium-magnesium alloys, which are often found in cell phones and other electronic gadgets that must be strong yet light weight. Gardeners and tropical fish hobbyists are also very familiar with magnesium, since plants need it to grow (a magnesium deficiency is indicated by yellow leaves).  Animals need small amounts of magnesium to support proper bodily functions too.

For more information visit:-
http://en.wikipedia.org/wiki/Magnesium
http://www.theguardian.com/science/punctuated-equilibrium/2011/may/13/1?guni=Article:in%20body%20link

Holmium

Holmium is a chemical element with the symbol Ho and atomic number 67 and is a rare earth element. It was discovered by Swedish chemist Per Theodor Cleve. Its oxide was first isolated from rare earth ores in 1878 and the element was named after the city of Stockholm.

It is a relatively soft and malleable silvery-white metal. It is too reactive to be found uncombined in nature, but when isolated, is relatively stable in dry air at room temperature. However, it reacts with water and rusts readily, and will also burn in air when heated.

Holmium has the highest magnetic strength of any element and therefore is used for the polepieces of the strongest static magnets.

Holmium oxide appears to have different colours depending on changes in ambient lighting. Under natural light, it's yellow, but under fluorescent lighting, it's pink.

Ho₂O₃, left: natural light, right: fluorescent lamp light

Holmium is used in yttrium-iron-garnet (YIG)- and yttrium-lanthanum-fluoride (YLF) solid-state lasers found in microwave equipment (which are in turn found in a variety of medical and dental settings). Holmium lasers emit at 2.08 micrometres, and therefore are safe to eyes^. They are used in medical, dental, and fibre-optical applications.

Holmium is one of the colorants used for cubic zirconia and glass, providing yellow or red colouring.  Glass containing holmium oxide and holmium oxide solutions (usually in perchloric acid) have sharp optical absorption peaks in the spectral range 200–900 nm. They are therefore used as a calibration standard for optical spectrophotometers and are available commercially.

For more information visit:-
http://en.wikipedia.org/wiki/Holmium
http://www.theguardian.com/science/grrlscientist/2012/aug/10/1?guni=Article:in%20body%20link

Cobalt!

Cobalt is a chemical element with symbol Co and atomic number 27. Like nickel, cobalt in the Earth's crust is found only in chemically combined form, save for small deposits found in alloys of natural meteoric iron. The free element, produced by reductive smelting, is a hard, lustrous, silver-grey metal.

Cobalt-based blue pigments (cobalt blue) have been used since ancient times for jewellery and paints, and to tint glass blue, but the colour was later thought by alchemists to be due to the known metal bismuth. Miners had long used the name kobold ore (German for goblin ore) for some of the blue-pigment producing minerals; they were named because they were poor in known metals, and gave poisonous arsenic-containing fumes upon smelting. In 1735, such ores were found to be reducible to a new metal (the first discovered since ancient times), and this was ultimately named for the kobold.

Cobalt is primarily used as the metal, in the preparation of magnetic, wear-resistant and high-strength alloys. Its compounds cobalt silicate and cobalt(II) aluminate (CoAl₂O₄, cobalt blue) give a distinctive deep blue color to glass, ceramics, inks, paints and varnishes.

Cobalt blue tinted glass

Free cobalt (the native metal) is not found in on Earth, except as recently delivered in meteoric iron (see below). Though the element is of medium abundance, natural compounds of cobalt are numerous. Small amounts of cobalt compounds are found in most rocks, soil, plants, and animals.

Cobalt forms many useful alloys. It is alloyed with iron, nickel, and other metals to form Alnico, an alloy with exceptional magnetic strength. Cobalt, chromium, and tungsten may be alloyed to form Stellite, which is used for high-temperature, high-speed cutting tools and dies. Cobalt is used in magnet steels and stainless steels. It is used in electroplating because of its hardness and resistance to oxidation. Cobalt salts are used to impart permanent brilliant blue colours to glass, pottery, enamels, tiles, and porcelain. Cobalt is used to make Sevre's and Thenard's blue. A cobalt chloride solution is used to make a sympathetic ink. Cobalt is essential for nutrition in many animals. Cobalt-60 is an important gamma source, tracer, and radiotherapeutic agent.



For more information visit:-
http://en.wikipedia.org/wiki/Cobalt
http://www.theguardian.com/science/punctuated-equilibrium/2011/sep/02/1?guni=Article:in%20body%20link

Thorium

Thorium has been in the news recently as it was suggested as a safer and more readily available element than Uranium for generating power.

Thorium is a naturally occurring radioactive chemical element with the symbol Th and atomic number 90. It was discovered in 1828 by the Norwegian mineralogist Morten Thrane Esmark and identified by the Swedish chemist Jöns Jakob Berzelius and named after Thor, the Norse god of thunder.

Thorium produces a radioactive gas, radon-220, as one of its decay products. Secondary decay products of thorium include radium and actinium. In nature, virtually all thorium is found as thorium-232, which undergoes alpha decay with a half-life of about 14.05 billion years. Other isotopes of thorium are short-lived intermediates in the decay chains of higher elements, and only found in trace amounts. Thorium is estimated to be about three to four times more abundant than uranium in the Earth's crust, and is chiefly refined from monazite sands as a by-product of extracting rare earth metals.

Pure thorium is a soft, lustrous silvery-white metal. If it doesn't burst into flames first, thorium will slowly tarnish when exposed to air, becoming grey, as you see above, and then finally black in colour. Thorium is very ductile and, like all actinoids, thorium is radioactive.

Monazite, a rare earth and thorium phosphate mineral, is the primary source of the world's thorium

When compared to uranium, there is a growing interest in developing a thorium fuel cycle due to its greater safety benefits, absence of non-fertile isotopes and its higher occurrence and availability.

India's Kakrapar-1 reactor is the world's first reactor which uses thorium rather than depleted uranium to achieve power flattening across the reactor core. India, which has about 25% of the world's thorium reserves, is developing a 300 MW prototype of a thorium-based Advanced Heavy Water Reactor (AHWR). The prototype is expected to be fully operational by 2016, after which five more reactors will be constructed. The reactor is a fast breeder reactor and uses a plutonium core rather than an accelerator to produce neutrons. As accelerator-based systems can operate at sub-criticality they could be developed too, but that would require more research. India currently envisages meeting 30% of its electricity demand through thorium-based reactors by 2050.



For more information visit:-
http://en.wikipedia.org/wiki/Thorium
http://www.theguardian.com/science/grrlscientist/2013/jun/07/1?guni=Article:in%20body%20link
http://en.wikipedia.org/wiki/Thorium-based_nuclear_power
http://www.bbc.co.uk/news/science-environment-24638816

Polish that Chrome!

Chromium is the first of the group 6 transition metals. It is denoted by the symbol Cr and atomic number 24. Chromium is a grey coloured, hard and very lustrous metal.  It takes a high polish, resists tarnishing, and has a high melting point. The name of the element is derived from the Greek word "chrōma" (χρώμα), meaning colour.

Chromium is highly corrosion resistant, a character that it brings with it when added to steel to create stainless steel. Another popular use for chromium is electroplating, which gives hubcaps, bumpers and other shiny bits of cars their street-cred.

Many of its compounds are intensely coloured. Besides providing the familiar non-fading "chrome yellow" colour used on American school buses and by the German postal service, there is the bright red pigment, chrome red (PbCrO₄·Pb(OH)₂), a bright green (Cr₂O₃), a pale green ([CrCl(H₂O)₅]Cl₂), and rich violet ([Cr(H₂O)₆]Cl₃). Trace amounts of chromium also gives rubies and emeralds their characteristic colours.

Below is the relatively rare mineral, crocoite (PbCrO₄), the state mineral of Tasmania.

Chromium is the 24th most abundant element in Earth's crust with an average concentration of 100 ppm. Chromium compounds are found in the environment, due to erosion of chromium-containing rocks and can be distributed by volcanic eruptions. The concentrations range in soil is between 1 and 300 mg/kg, in sea water 5 to 800 µg/litre, and in rivers and lakes 26 µg/litre to 5.2 mg/litre.  Chromium is mined as chromite (FeCr₂O₄) ore.  About two-fifths of the chromite ores and concentrates in the world are produced in South Africa, while Kazakhstan, India, Russia, and Turkey are also substantial producers. Untapped chromite deposits are plentiful, but geographically concentrated in Kazakhstan and southern Africa

In the laboratory Chromic acid is a powerful oxidizing agent and is a useful compound for cleaning laboratory glassware of any trace of organic compounds. It is prepared in situ by dissolving potassium dichromate in concentrated sulfuric acid, which is then used to wash the apparatus. Sodium dichromate is sometimes used because of its higher solubility (50 g/L versus 200 g/L respectively). The use of dichromate cleaning solutions is now phased out due to the high toxicity and environmental concerns. Modern cleaning solutions are highly effective and chromium free. Potassium dichromate is a chemical reagent, used as a titrating agent. It is also used as a mordant (i.e., a fixing agent) for dyes in fabric.

For more information visit:-
http://www.theguardian.com/science/punctuated-equilibrium/2011/aug/12/1?guni=Article:in%20body%20link
http://en.wikipedia.org/wiki/Chromium

The Periodic Table

The Periodic Table

A periodic table is a tabular display of the chemical elements, organized on the basis of their atomic numbers, electron configurations, and recurring chemical properties. Elements are presented in order of increasing atomic number (number of protons). The standard form of table comprises an 18 × 7 grid or main body of elements, positioned above a smaller double row of elements. The table can also be deconstructed into four rectangular blocks: the s-block to the left, the p-block to the right, the d-block in the middle, and the f-block below that. The rows of the table are called periods; the columns of the s-, d-, and p-blocks are called groups, with some of these having names such as the halogens or the noble gases. Since, by definition, a periodic table incorporates recurring trends, any such table can be used to derive relationships between the properties of the elements and predict the properties of new, yet to be discovered or synthesized, elements. As a result, a periodic table—whether in the standard form or some other variant—provides a useful framework for analyzing chemical behavior, and such tables are widely used in chemistry and other sciences.

 

Although precursors exist, Dmitri Mendeleev is generally credited with the publication, in 1869, of the first widely recognized periodic table. He developed his table to illustrate periodic trends in the properties of the then-known elements. Mendeleev also predicted some properties of then-unknown elements that would be expected to fill gaps in this table. Most of his predictions were proved correct when the elements in question were subsequently discovered. Mendeleev's periodic table has since been expanded and refined with the discovery or synthesis of further new elements and the development of new theoretical models to explain chemical behaviour.

 

Download a copy here.

http://en.wikipedia.org/wiki/Periodic_table
http://iupac.org/