borax Sodium borate, Na2B4O7.10H2O, a salt of boric acid used in cosmetics and detergents, in glazes in the ceramics industry, and since ancient Egyptian times as a flux in metalworking.
buckyball Also known as buckminsterfullerene, a spherical carbon molecule with formula C60. It has a structure like a football, containing 12 pentagons and 20 hexagons with a carbon atom at each vertex (corner/intersection). It is an example of a fullerene, a type of carbon molecule in the shape of a sphere or tube. Buckminsterfullerene was the first fullerene discovered and was produced in 1985 by Richard Smalley, Robert Curl, James Heath, Sean O’Brien and Harry Kroto. The name of the molecule is a tribute to American polymath R. Buckminster Fuller (1895–1983) because its shape recalls the geodesic dome that he developed.
dopant Trace amount of impure material added to a pure material; used, for example, in controlling the conductivity of a semiconductor.
doping In general, the addition of impurities. In the context of semiconductors, doping means adding very small amounts of impure materials to pure semiconductors to control their conductivity. For example, adding 10 atoms of boron per million atoms of silicon increases the conductivity of silicon by a factor of 1000. Doping agents are also added to phosphors to produce a specific colour in the glow they give off when stimulated by ultraviolet light or electrons. The lanthanide element europium is used in this way.
electron hole A theoretical concept used by chemists, physicists and electronic engineers to describe a gap that an electron could occupy in an atom. The gap will attract an available electron.
electroplating Coating a material with a very thin layer of metal using electrolysis such as in chrome or gold plating. The material being coated must be able to conduct electricity; it is either a conductive metal or a material made conductive by techniques including covering with lacquer or graphite.
flux Cleaning or purifying substance used in metalworking, for example, to remove oxides from the surfaces of molten metals. Fluxes are also used in smelting ores to make metals flow more easily.
hydride Chemical compound in which hydrogen and another element are combined.
N-type material A material, typically a semiconductor, treated with impurities (dopants) to make it have more conductive electrons than electron holes. An example is silicon doped with arsenic or phosphorus.
P-type material A material, typically a semiconductor, treated with impurities (dopants) to make it have more electron holes than conductive electrons. An example is silicon doped with boron or aluminium.
semiconductor Material with electrical conductivity between that of a conductor (which allows an electrical charge to flow easily through it) and an insulator (which prevents an electrical charge flowing easily through it). Semiconductors have good conductivity in certain conditions, depending on factors such as temperature, magnetic fields or the addition of impurities (doping). Some semiconductors are elements, for example, tin, silicon and germanium; other semiconductors are compounds, for example, gallium arsenide.
semi-metal Another term for metalloid, an element that is intermediate between a metal and a non-metal. Examples include aluminium and germanium.
sublimation Passing directly from solid to gaseous state without becoming a liquid.
METALLOIDS
Metalloids are found in groups 13–16 of the periodic table. They have characteristics of non-metals and of metals. Metalloids such as boron, germanium and silicon are semiconductors and are used in computer chips.
Metalloids
|
Symbol |
Atomic Number |
Boron |
B |
5 |
Silicon |
Si |
14 |
Germanium |
Ge |
32 |
Arsenic |
As |
33 |
Antimony |
Sb |
51 |
Tellurium |
Te |
52 |
Polonium |
Po |
84 |
Boron is the third lightest solid non-metal, very different from aluminium and the other metals in its group. It was first obtained, as light but very hard, dark grains, by British chemist Humphry Davy in London, and – independently of Davy – by the French chemists Louis-Joseph Gay-Lussac and Louis-Jacques Thénard, working together, in Paris in 1808. Boron is scarce but widely distributed in the earth’s crust, and there are a few rich deposits of borates, in which the element is combined with oxygen and calcium or sodium; the latter (borax) has been used since ancient times as a flux for working with molten metals. Boron is essential to plant life and as a micronutrient for animals, toxic only in excess. It combines with carbon in a very hard ceramic, used in tank armour, bullet-proof vests and many industrial applications, and also to shield nuclear reactors. One of boron’s compounds with nitrogen has the structure of diamond and is almost as hard, but is more heat resistant and therefore a valuable abrasive. There is also a form like graphite. Boric acid is an antiseptic and is one of the few things that can kill cockroaches.
3-SECOND STATE
Chemical symbol: B
Atomic number: 5
Named: From Arabic buraq, via Latin borax (sodium borate)
3-MINUTE REACTION
Like those of carbon, boron atoms stick readily to each other as well as to atoms of metals and non-metals, giving rise to a complex chemistry. They spontaneously arrange themselves at the 12 corners of a 20-faced ball, reminiscent of carbon ‘buckyballs’, and these can be necklaced together by atoms of other elements such as carbon. With hydrogen atoms attached, boron atoms join in chains and rings to form a bewildering number of boranes.
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3-SECOND BIOGRAPHIES
HUMPHRY DAVY
1778−1829
British chemist who isolated boron in 1808
LOUIS-JACQUES THÉNARD & LOUIS-JOSEPH GAY-LUSSAC
1777–1857 & 1778–1850
French chemists who isolated boron, also in 1808
30-SECOND TEXT
P.J. Stewart
Found in pesticides against cockroaches, boron also features in tank armour. Louis-Jacques Thénard (top) and Louis-Joseph Gay-Lussac were two of its discoverers.
Every valley is really a silicon valley. Silicate minerals, containing frameworks of silicon and oxygen atoms, comprise most of the earth’s crust; silicon is the crust’s second most abundant element, after oxygen. However, despite this ubiquity, pure silicon was not isolated until 1824, because it is hard to separate it from oxygen. Much of mineral chemistry centres on the various ways that silicate ions – tetrahedra with silicon at the centre and oxygen atoms at the four corners – can be joined into orderly, crystalline networks that house metallic elements such as sodium and calcium. In glass, this silicon-oxygen network is melted and refrozen into static disorder. Today, the ultra-pure silicon needed for microelectronics is mostly made by electrolysis of low-purity silicon or its compounds, followed by melting and controlled crystallization to make the near-perfect crystals needed for silicon wafers. Silicon is a semiconductor. It contains just a few ‘free’ electrons that can carry an electrical current. The number of these mobile electrons, and thus the electrical conductivity, can be finely tuned by adding small quantities of impurities (‘dopants’) such as boron and phosphorus; this is why silicon is so useful for making microelectronic devices such as transistors.
3-SECOND STATE
Chemical symbol: Si
Atomic number: 14
Named: From Latin silex (‘hard rock’)
3-MINUTE REACTION
Silicon is regularly confused with silicone, a class of polymers whose backbones are chains of alternating silicon and oxygen atoms. In silicones, each silicon atom has hydrocarbon appendages. Developed in the early 20th century, silicones range, like hydrocarbon polymers, from oils to tough plastics, finding uses such as lubricants, sealants, adhesives, electrical insulation, cookware, and – controversially – breast implants. The ability of silicon to form polymers analogous to hydrocarbons sparks speculation about silicon-based alien life.
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3-SECOND BIOGRAPHIES
JÖNS JAKOB BERZELIUS
1779–1848
Swedish chemist, the first person to isolate fairly pure silicon, in 1824
VICTOR MORITZ GOLDSCHMIDT
1888–1947
Swiss mineralogist who deduced the crystal structures of many silicate minerals
30-SECOND TEXT
Philip Ball
As a key ingredient of rocks and stones, silicon has a history of human use reaching back to the Stone Age, despite modern associations with computing and hi-tech industries.
When Russian chemist Dmitri Mendeleev drew up the periodic table of elements, he found gaps where he predicted unknown elements would sit. One, which he called ‘eka-silicon’, proved to be germanium. Mendeleev predicted its atomic weight, its density and even that this semi-conducting metalloid would be grey. German chemist Clemens Winkler, who in 1886 discovered the actual element, intended to call his find ‘neptunium’, but discovered that another element had been given that name, so went for the Latin term for the newly formed Deutschland. Ironically, neptunium came free again, because the other discovery proved to be an error. Germanium found its niche in the 20th century as the leading component of early solid-state electronics, replacing expensive and fragile glass valves (vacuum tubes). Until the 1970s, germanium transistors and diodes were common, but silicon took over the mass market – partially because silicon is so cheap (the raw material is sand), and also because it is more effective as a semiconductor; germanium had got its head start because sufficiently pure silicon was not widely available before. However, this hasn’t meant the disappearance of germanium from electronics. Fibre-optic cable equipment and night vision goggles still make use of this robust semiconductor.
3-SECOND STATE
Chemical symbol: Ge
Atomic number: 32
Named: From Latin Germania (name for the German region)
3-MINUTE REACTION
Germanium first found large-scale use as a replacement for the diode valve. The valve acts as a one-way mechanism, only allowing current to flow in one direction; a semi-conductor like germanium provides a solid-state equivalent. When impurities are added, germanium can become an electron donor (n-type material) or electron acceptor (p-type); by combining strips of the different types of germanium, electrons can be limited to travelling in a single direction.
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3-SECOND BIOGRAPHIES
DMITRI MENDELEEV
1834–1907
Russian chemist who predicted the existence of germanium from his periodic table
CLEMENS WINKLER
1838–1904
German chemist who discovered germanium in 1886
30-SECOND TEXT
Brian Clegg
While rhenium is named for the River Rhine, germanium – initially called ‘eka-silicon’ by Dmitri Mendeleev (right) – takes its title from the country of Germany.
Arsenic is a semimetal, best known as its oxide (white arsenic), used as a poison over many centuries. White arsenic was scraped from the flues of copper refineries when ores rich in arsenic were smelted and, despite its toxicity, became popular in medicine from 1780 onward – as ‘Dr. Fowler’s Solution’, which was prescribed for all kinds of ailments but with little benefit. The arsenic medicine Salvarsan, discovered in 1909, cured parasitic infections of the blood such as syphilis, and white arsenic reappeared as the medicine arsenic trioxide, now used to treat leukemia. Accidental arsenic poisoning appeared to be a threat in the 19th century due to the green pigment copper arsenite, used in wallpapers; when it became damp, it could give off trimethylarsine vapour and was thought to cause arsenic poisoning, maybe even of the deposed French emperor Napoleon in 1821. Then, in 2005, it was shown that this gas is not particularly toxic. Arsenic-based weedkillers and wood preservatives have now been phased out, and today arsenic is more likely to be used as the semiconductor gallium arsenide (GaAs). Arsenic is present in foods, such as prawns, but in a form that poses no threat to health.
3-SECOND STATE
Chemical symbol: As
Atomic number: 33
Named: After Greek arsenikon (the mineral yellow orpiment)
3-MINUTE REACTION
A semimetal in group 15 of the periodic table, arsenic can bond to three other atoms, as in the deadly gas arsine (AsH3); or to five atoms, in compounds such as the pentachloride (AsCl5). It has two oxides, As2O3 and As2O5. Arsenic forms two kinds of salts: arsenites (which have the negative ion AsO33-) and arsenates (negative ion AsO43-). When it is strongly heated, arsenic sublimes (which passes from solid to gas without becoming liquid) at 616°C (1,141°F).
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3-SECOND BIOGRAPHIES
ALBERTUS MAGNUS
1193–1280
German friar who was the first person to separate arsenic
CARL WILHELM SCHEELE
1742–86
German-Swedish chemist who discovered the copper arsenite dye called Scheele’s green in 1775
PAUL EHRLICH
1854–1915
German doctor who discovered Salvarsan as a cure for syphilis
30-SECOND TEXT
John Emsley
Famous for its poisonous oxide, it has also been used for more than two centuries in medicine and is today used in treating leukaemia.
Assyrians and ancient Egyptians decorated their eyes with the black mineral stibnite (antimony sulphide), from which antimony gets its chemical symbol Sb. To the Assyrians, stibnite was guhlu, which became Arabic kohl – a word still in use for eyeliner; al-kohl came to be used for any fine powder, and then for distilled liquids, transferring finally to the English word ‘alcohol’. Stibnite could cure eye infections and was considered a powerful medicine. Medieval alchemists revered its medicinal powers, and the pseudonymous chemist Basil Valentine celebrated it in a 1604 book The Triumphal Chariot of Antimony. The 17th century saw the Antimony Wars, in which French chemists argued over whether antimony was poison or cure. In fact, the element is quite toxic, and Basil Valentine claimed that when he administered it in a monastery, some of the monks died – accounting for the probably apocryphal etymology anti-monachos: ‘anti-monk’. Antimony was a favourite slow poison among Victorian murderers. Pure antimony, first made in the 16th century, looks like a silvery metal, but it is a metalloid, with properties in between a metal and non-metal. It conducts electricity but is soft, and it is mostly used now in alloys of lead and tin for solders and lead-acid battery electrodes.
3-SECOND STATE
Chemical symbol: Sb
Atomic number: 51
Named: Disputed etymology – possibly Arabic or Greek
3-MINUTE REACTION
Antimony’s toxicity can cause vomiting when it is ingested. This led to its use as a medieval ‘purgative’ – it was considered a good way to expel disease from the body. By the same token it has laxative properties, and constipation caused by the poor diet of the Middle Ages was cured by swallowing tablets of pure antimony. The tablets were not absorbed by the body, but were excreted – and recovered for reuse.
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3-SECOND BIOGRAPHIES
JOHN OF RUPESCISSA
c. 1310—c. 1362
French alchemist who considered antimony central to alchemical medicine
JOHANN THÖLDE
1565–1614
German publisher, and probable author under the name Basil Valentine, of The Triumphal Chariot of Antimony (1604)
30-SECOND TEXT
Philip Ball
One theory about the death at only 35 of Austrian composer Wolfgang Amadeus Mozart (top right) is that he was poisoned by excessive ‘medicinal’ doses of antimony.
Tellurium was the metallum problematum (‘problem metal’) for 16 years after its discovery in 1782 in gold ores from Transylvania (now part of Romania). The properties of the ores indicated that the substance had metallic and non-metallic properties, so it was also called aurum paradoxum (‘paradoxical gold’). Tellurium was identified as an element in 1798. In 1834, Swedish chemist Jöns Jacob Berzelius decided it was a metal, but one that belonged in the same group as the non-metals sulphur and selenium due to the similarities of their compounds; it is now recognized as a metalloid. Tellurium is about 15 per cent less dense than iron and marginally harder than sulphur. It is easily pulverized and too brittle for structural uses; its primary use is as an additive to improve the machining qualities, or workability, of various metals, chiefly stainless steels and copper. Occasionally found native as elemental crystals, it combines easily with most other elements to form tellurides. The semiconducting materials bismuth telluride and lead telluride are used in thermoelectric devices as sources of electricity or for cooling. Cadmium telluride thin-film solar cells, used to generate electric power, are amongst the lowest-cost type of solar cell.
3-SECOND STATE
Chemical symbol: Te
Atomic number: 52
Named: From Latin tellus (‘earth’/’the earth’)
3-MINUTE REACTION
Tellurium is extremely rare in the earth’s crust, partially due to the fact that its formation of a volatile hydride caused the element to be lost to space as a gas during the hot nebular formation of the earth. It is highly toxic. In the body, it is partially metabolized to the gas dimethyl telluride, which can be smelled in ‘tellurium breath’, an unpleasant garlic-like odour identifiable in the breath of people who have been exposed to tellurium.
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3-SECOND BIOGRAPHIES
FRANZ-JOSEPH MÜLLER VON REICHENSTEIN
1740–1826
Austrian mining engineer who discovered tellurium in gold ore in 1782
MARTIN HEINRICH KLAPROTH
1743–1817
German chemist who named tellurium in 1798
30-SECOND TEXT
Jeffrey Owen Moran
‘Garlic breath’ can have consequences more serious than social embarrassment, it may mean you have tellurium poisoning. Tellurium can damage your liver and nerves.
Millions of people across the world owe their lives to the pioneering work of Marie Curie. She overcame poverty, sexism and illness to pursue her passion for physics and, along with her husband Pierre, discovered radium, which would be used in radiation therapy to treat cancer. Marie was the first woman to win a Nobel Prize and dedicated her life to study of the therapeutic possibilities of radiotherapy.
Born Maria Sklodowska in Warsaw in 1867, Marie showed an early gift for physics. Women were banned from attending university in Warsaw at that time, so she had to work as a governess to scrape together the funds to study at the Sorbonne in Paris. In 1894, she met Pierre Curie, a professor of physics, and their marriage marked the beginning of a groundbreaking scientific collaboration.
The scientific community was hugely excited in 1896 when Henri Becquerel discovered that uranium emitted radiation. The Curies were intrigued and began to examine uranium ore (pitchblende). They deduced that the ore was more radioactive than uranium itself, and that it must, therefore contain other radioactive elements. After years of painstaking research – suffering ill health and exhaustion – the Curies made history by discovering the highly radioactive elements polonium and radium. No one would dare handle radium now, but the Curies were determined to experiment and found that when applied to human flesh radium could burn and wound. It was this discovery that led to the use of radium in the treatment of cancerous tumours.
Awards and honours began to flood in, and in 1903 Marie made history by becoming the first woman to win a Nobel Prize, which she shared with Becquerel and Pierre. Pierre died in a road accident in 1906, but Marie continued their work at the Sorbonne. She made history again in 1911 by being awarded a second Nobel Prize, this time for chemistry, in recognition of her achievements in the study of radium.
During the First World War, she pioneered the use of mobile radiography units to diagnose injuries, and drove the ambulances herself. After the war, her health began to decline and she died of leukaemia in 1934; this may have been caused by exposure to radioactive material. Marie’s name will always be synonymous with the fight against cancer and as history’s greatest female scientist she has inspired many women to explore the previously male-dominated fields of physics and chemistry.
Born in Warsaw
1891
Moves to Paris to study mathematical sciences and physics at the Sorbonne
1895
Marries Pierre Curie
1897
Daughter Irène born
1898
The Curies discover polonium and radium
1903
Becomes the first woman to receive a doctorate of science at the Sorbonne
1903
Jointly awarded the Nobel Prize for Physics with Pierre and Becquerel
1904
Daughter Ève born
1906
Pierre dies in a road accident
1906
Becomes the first ever female professor at the Sorbonne
1911
Wins a Nobel Prize for chemistry
1914
Appointed a director of the newly founded Radium Institute in Paris
1934
Dies in France of leukemia
1995
The Curies’ remains are reinterred in the Panthéon, Paris
A chemical curiosity from the bottom of the periodic table, polonium is a silvery-white metal of which few people have seen even a speck. This mysterious element is known less for its chemistry than for its physical properties. It was discovered in Paris in 1898 by the Polish-born physicist Marie Curie and her French physicist husband, Pierre, who together isolated it as one of the minor but more radioactive components of pitchblende, a uranium-containing mineral. So radioactive is the metal that it has few uses. However, trace amounts of polonium are incorporated into anti-static devices for the textile, electronics, printing and munitions industries, where sparks would pose a fire or explosion risk. In a remarkable example of fighting fire with fire, the ions produced by polonium’s intense radioactivity neutralize any localized build-up of static charge. Polonium became notorious in 2006 when Alexander Litvinenko, a Russian émigré living in London, became mysteriously ill. Doctors at London hospitals took several days to realize that he was suffering from radiation poisoning, the result of swallowing a drink laced with polonium widely believed to have been administered by Russian agents. Litvinenko died in agony three weeks later.
3-SECOND STATE
Chemical symbol: Po
Atomic number: 84
Named: For Poland, birth country of discoverer, Marie Curie
3-MINUTE REACTION
Because natural polonium is so radioactive that an ingot would be hot to the touch, very little is known about its properties – it is just too dangerous to study in ordinary labs. The metal can be dissolved in dilute acids to form salts, electroplated and even distilled under vacuum. The handful of its compounds that have been made – for example, oxide, chloride, bromide – suggest similarities with tellurium and bismuth.
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3-SECOND BIOGRAPHIES
HENRI BECQUEREL
1852–1908
French physicist who discovered radioactivity in pitchblende
MARIE CURIE
1867–1934
Polish-born physicist who discovered polonium in samples of pitchblende and purified the element
30-SECOND TEXT
Andrea Sella
Polonium was the first element discovered by radiochemical analysis. Its longest-lived isotope has a half-life of 103 years; its most common isotope has a half-life of 138 days.
