alpha particle Type of particle consisting of two protons and two neutrons, identical to a helium nucleus. It is emitted from an atomic nucleus undergoing alpha decay, a type of radioactive decay.
alpha process One of two classes of nuclear fusion reaction by which stars convert helium into heavier elements. (The other type is the triple-alpha process.)
diatomic molecule A molecule containing just two atoms. These two atoms can be of the same element (for example oxygen, O2) or two different elements (for example carbon monoxide, CO).
electrolysis Technique that uses an electric current to bring about a chemical reaction. It is used on ionic substances (materials formed when a non-metal reacts with a metal, which contain charged particles or ions). When the current passes through the ionic substance (the electrolyte), negative ions move to the positive electrode (anode) – where they lose electrons and are oxidized – while positive ions move to the negative electrode (cathode), where they gain electrons and are reduced. Electrolysis is used commercially in processes to separate elements from their natural sources such as ores.
fluorinate To combine or treat with fluorine or a fluorine compound.
inert A substance that does not undergo a chemical reaction. The ‘noble gases’ were at one time known as the inert gases.
nucleon Particle within the nucleus of an atom, either a positively charged proton or an electrically neutral neutron. Each nucleon consists of three quarks.
oxidation Generally a chemical reaction in which atoms react with oxygen, an example being when a metal rusts. More technically oxidation is a reaction in which at least one electron is lost from one of the two substances involved.
oxidation number An artificial, but useful, concept obtained by assuming that an element is bonded ionically and counting the number of electrons gained or lost.
oxidation state Alternate name for oxidation number.
oxide Chemical compound in which oxygen combines with another element.
polymer Chemical compound that contains long chains, typically of carbon atoms. Polymers are created through a process called polymerization.
redox reactions Also called oxidation reduction reactions, chemical reactions in which oxidation and reduction take place.
reduction The opposite of the technical meaning of oxidation – that is, a reaction in which one or more electrons is gained.
substitution reaction Chemical reaction in which one element in a compound (an atom, ion or group of atoms/ions) is replaced by another element.
HALOGENS AND NOBLE GASES
The halogens and noble gases are in groups 17 and 18 of the periodic table. The halogens are non-metallic elements; all have seven electrons in their outer shell. The noble gases all have full outer shells of electrons and so do not readily form compounds. They are called ‘noble gases’ because they rarely react with other elements – a reference to members of the nobility who traditionally kept themselves aloof from other people in society.
Halogens
|
Symbol |
Atomic Number |
Fluorine |
F |
9 |
Chlorine |
Cl |
17 |
Bromine |
Br |
35 |
Iodine |
I |
53 |
Astatine |
At |
85 |
Noble Gases
|
Symbol |
Atomic Number |
Helium |
He |
2 |
Neon |
Ne |
10 |
Argon |
Ar |
18 |
Krypton |
Kr |
36 |
Xenon |
Xe |
54 |
Radon |
Rn |
86 |
Early chemists knew that the mineral fluorspar (calcium fluoride), used in welding metals and etching glass, contained an unknown element, but they could not isolate it. This element was eventually obtained in 1886 by French chemist Henri Moissan, as the pale yellow gas fluorine, by the electrolysis of potassium fluoride in liquid hydrogen fluoride. Fluorine is still produced by this method and is used in the manufacture of products such as Teflon, a fluorinated polymer used for cable insulation, tubing, fabric roofing, plumber’s tape, non-stick pans and the wet-weather gear Gore-Tex; another use for Gore-Tex is in artificial veins and arteries. Fluorine is now generally diluted with nitrogen. When polythene containers are treated with this gas, an impenetrable fluorinated layer is formed; these containers make ideal fuel tanks because they are less likely than conventional tanks to rupture in a crash. Fluorine is also used to make uranium hexafluoride, and thereby separate the isotope uranium-235 (the fuel of nuclear reactors). Fluoride (F−) strengthens bones and teeth by converting the calcium phosphate of which they are made to a harder mineral, fluoroapatite. Some medicinal molecules have a fluorine atom incorporated: these such as the antifungal medicine fluconazole can be highly effective treatments.
3-SECOND STATE
Chemical symbol: F
Atomic number: 9
Named: From Latin fluere (‘to flow’)
3-MINUTE REACTION
Fluorine is the first member of group 17 (the halogens). It will react chemically with all the other elements except helium and neon. Fluorine exists only as the isotope, fluorine-19, which is not radioactive. However, radioactive fluorine-18 can be made and is the basis of positron emission tomography (PET), a medical imaging technique that produces a 3D image of organs and bodily processes: with a half-life of 110 minutes, fluorine-18 decays in a way that allows doctors to monitor the body’s vital organs.
RELATED ELEMENTS
3-SECOND BIOGRAPHIES
HENRI MOISSAN
1852−1907
French chemist who first produced fluorine gas in 1886 in Paris
FREDERICK MCKAY
1874−1959
American dentist who proved in the early 1930s that fluoride strengthens teeth
ROY PLUNKETT
1911−94
American chemist who in 1938 discovered Teflon
30-SECOND TEXT
John Emsley
How do chemical elements contribute to cooking eggs? Fluorine (in Teflon) coats your non-stick skillet.
A substance that appears to be chlorine was described in the 1630s by Flemish chemist Jan Baptista van Helmont, was spotted in 1774 by German-Swedish chemist Carl Wilhelm Scheele, who called it ‘dephlogisticated muriatic acid air’, and was identified as an element and given its modern name by British chemist Humphry Davy in 1810. Chlorine is widely available thanks to its presence in seawater. Although we think the sea is salt (sodium chloride) water, it actually contains separate sodium and chloride ions from different sources; salt forms only when the water is evaporated. Chlorine is produced from saline solution by electrolysis: the negatively charged chloride ions are attracted to a positive electrode. Chlorine’s disinfectant and antiseptic qualities make it valuable in bleaches and in treating drinking water, in addition to its role in swimming pools. Chlorine’s dark side was first unleashed on 22 April 1915, when 6,000 cylinders along the German army’s front line were used against Algerian troops of the French army near Ypres. This terrifying weapon was the work of German chemist Fritz Haber. Chlorine burns away the lining of the lungs, leaving victims drowning in the fluid that oozes out.
3-SECOND STATE
Chemical symbol: Cl
Atomic number: 17
Named: From Greek khlôros (‘pale green’)
3-MINUTE REACTION
As a powerful oxidizer, chlorine is widely used as a germ killer. ‘Oxidizing’ originally referred to a reaction – such as rusting – that involves adding oxygen to a compound, but is now more generally a reaction that removes electrons. When chlorine attacks bacteria, the oxidizing action breaks down the cell membrane, killing the micro-organism. The element is usually added in the form of a compound such as sodium hypochlorite; nevertheless, it is the chlorine that does the work.
RELATED ELEMENTS
3-SECOND BIOGRAPHIES
JAN BAPTISTA VAN HELMONT
1579–1644
Flemish chemist who made the first recorded production of chlorine
CARL WILHELM SCHEELE
1742–86
German-Swedish chemist who properly discovered chlorine gas
HUMPHRY DAVY
1778–1829
British chemist who confirmed chlorine as an element and named it
30-SECOND TEXT
Brian Clegg
The distinctive odour of chlorine summons images of swimming pools, yet the element also brings to mind the horrors of chemical warfare in the First World War trenches.
Among the non-metallic elements, iodine is probably the one with which we are most familiar in the home. It lives in the medicine cupboard, where the properties it shares with its fellow halogens – such as the more reactive chlorine – make it ideal for dabbing on cuts and grazes. Canadian poet and singer Leonard Cohen even wrote a song called ‘Iodine’, which refers to the compassionate sting of its chemical disinfectant action. The discovery of the element is one of the happiest accidents in chemistry. In 1811, French chemist Bernard Courtois used seaweed as a raw material at the family saltpetre works in Paris and noticed a bright violet vapour in the reaction vessel; the vapour condensed to form shiny black crystals. His compatriot Joseph-Louis Gay-Lussac confirmed that this was a new element, and suggested the name iodine. Unfortunately, Courtois was ruined in his efforts to profit from his discovery as his business failed to return on his investment and he stuggled financially for the rest of his life. Iodine’s medical applications were quickly realized. It began to be used to treat goitre, a deficiency of the thyroid gland. The knowledge that iodine is relatively abundant in seawater and marine plants explained why sea sponges had proved to be an effective folk remedy for goitre before.
3-SECOND STATE
Chemical symbol: I
Atomic number: 53
Named: From Greek iodes (‘violet’)
3-MINUTE REACTION
Because iodine atoms are bulky and form relatively weak single bonds, they are easily detached from certain molecules. This makes the element useful in substitution reactions in the organic chemistry used to make pharmaceuticals. An iodine atom bonded to an intermediate product in a chemical synthesis can be removed and replaced by a complex organic group with particular biomedical functions.
RELATED ELEMENTS
3-SECOND BIOGRAPHIES
HUMPHRY DAVY
1778–1829
British chemist mistakenly credited with discovery of iodine
LOUIS DAGUERRE
1787–1851
French scientist who made photographs using iodine-silver reaction
BASIL HETZEL
1922–
Australian campaigner against Third World iodine deficiency
30-SECOND TEXT
Hugh Aldersey-Williams
Commonly found in marine plants, iodine is used in the chemical industry as well as in disinfectants.
Element 85 has never been obtained in any amount large enough to be visible to the naked eye. If a visible sample were one day produced, it would immediately vapourize due to the heat generated by the radioactivity that would be emitted. Consequently, we can only estimate the bulk behaviour of astatine – for example, its melting and boiling points, or its colour. Nor do we know with any degree of confidence whether astatine forms diatomic molecules of At2, as happens with all other halogens. In 1943, three years after astatine was first synthesized artificially by scientists Dale Corson, Kenneth Mackenzie and Emilio Segrè in Berkley, California, the element was found to occur naturally in minute amounts in the earth’s crust: it is the rarest naturally occurring element, with a total of just 30 g (1 oz) in the crust at any given time. The longest lived isotope of astatine is At-210, with a half-life of 8.1 hours. Astatine has almost no applications, although one exception is the potential use in radiotherapy of At-211, an emitter of alpha particles with a convenient half-life of 7.2 hours. However, problems concerning the safe delivery of At-211 to humans continue to delay its implementation.
3-SECOND STATE
Chemical symbol: At
Atomic number: 85
Named: From Greek astatos (‘unstable’)
3-MINUTE REACTION
Like iodine, the element above it in the periodic table, astatine tends to find its way into the thyroid gland and could potentially be used to monitor medical conditions involving the thyroid and throat area in general. Moreover, the short-range nature of the emission of alpha particles by At-211 suggests that it could be used to treat cancers in all parts of the body whilst reducing the risks to neighbouring tissue.
RELATED ELEMENTS
3-SECOND BIOGRAPHIES
FRED ALLISON
1882–1974
American physicist who erroneously claimed to have discovered element 85 in 1930
EMILIO SEGRÈ, KENNETH MACKENZIE & DALE CORSON
1905–89, 1912–2002 & 1914–2012
American co-discoverers of astatine in 1940
30-SECOND TEXT
Eric Scerri
There are 33 known isotopes of the element astatine, including some naturally occurring in the earth’s crust.
Among the memorials inside Westminster Abbey, London, you’ll find names such as Sir Isaac Newton, Lord Nelson, Jane Austen and … Sir William Ramsay. This Glasgow-born scientist may not be a household name now, but in the late 19th and early 20th centuries he was a scientific celebrity, and in 1904 he became the first Briton to win the Nobel Prize for Chemistry. The accolade was awarded for his discovery of four gases (argon, krypton, neon and xenon), which – along with helium and radon – formed a new family of elements in the periodic table: the noble or inert gases.
Born in 1852, Ramsay was fascinated with chemistry as a child and studied at the University of Glasgow before completing a doctorate at Tübingen, Germany. Returning to Britain, he held a number of academic posts before being appointed to the prestigious chair of general chemistry at University College, London, which he held from 1887 to 1913. It was during this time that Ramsay made his most important discoveries.
In the mid-1890s, he became intrigued by the physicist Lord Rayleigh’s observation that nitrogen isolated from air had a slightly higher density than nitrogen obtained from chemical sources. Rayleigh believed there could be an impurity in the chemical sources, but Ramsay suspected that the anomaly could be caused by the presence of an undiscovered element in air that was mixed with the nitrogen. This marked the beginning of a fruitful collaboration with Rayleigh to test his theory.
Ramsay separated nitrogen from air and then passed it over heated magnesium, which produced a solid substance (magnesium nitride). He was left with around 1 per cent of residual gas that would not react, and on measuring it found it to be denser than nitrogen. The gas produced unique spectral lines and Ramsay knew he had found a new element in air, which he called argon.
Ramsay later isolated helium from the mineral cleveite, discovered the elements krypton, neon and xenon, and in 1910, proved that radon was a noble gas. Ramsay identified a whole new group in the periodic table, the noble gases, and Dmitri Mendeleev, the Russian chemist who discovered the table, eventually accepted his findings. The dapper Scottish chemist had made scientific history.
Born in Glasgow, Scotland
1866–70
Studies at the University of Glasgow
1870–72
Completes his doctorate at Tübingen, Germany
1872–80
Researches at Anderson College, Glasgow, and the University of Glasgow
1880
Appointed to the chair of Chemistry at University College, Bristol, England
1881
Marries Margaret Buchanan, with whom he has two children
1887
Becomes professor of general chemistry at University College, London
1888
Elected as a fellow of the Royal Society
1894
Discovers the new element argon
1895
Becomes the first chemist to isolate helium
1898
Discovers krypton, neon and xenon
1902
Knighted, becoming Sir William Ramsay
1903
Ramsay and Frederick Soddy isolate radon from radium
1904
Wins the Nobel Prize for Chemistry
1913
Retires and pursues interests in music, travel and poetry
23 July 23 1916
Dies in Buckinghamshire, England, of nasal cancer
This light noble gas makes up nearly one-quarter of the matter of the universe by mass – yet it was not noticed until 1868, when British astronomer Norman Lockyer found previously unknown spectral lines in the sun. Spectroscopy identifies elements present in a substance from dark lines that appear in a rainbow of light passed through a gas. Each element has a fingerprint of lines that can be used to identify it, even in the remote light from stars. French astronomer Jules Janssen also spotted the unexpected lines, but it was Lockyer who correctly identified this as a new element, which he named helium. In the 1890s, British chemist William Ramsay produced the gas when dissolving the mineral cleveite in acid. Helium is now primarily obtained as a by-product of natural gas extraction. We are familiar with helium in lighter-than-air party balloons. The gas produces a distinctive squeaky voice when inhaled because the speed of sound in helium is significantly higher than in air. Helium has also been used in airships. In addition, its very low boiling point of just above 4 kelvin (–269°C/–452°F) makes it ideal for cooling speciality equipment such as the magnets of MRI scanners.
3-SECOND STATE
Chemical symbol: He
Atomic number: 2
Named: For Greek helios (‘sun’), where the element was first discovered
3-MINUTE REACTION
Helium was one of the first elements to exist, created shortly after the Big Bang as the initial superheated ‘soup’ of matter cooled to form atoms, but more has been produced since by stars. The primary fuel of stars is hydrogen, which forms helium in nuclear fusion reactions. The helium nucleus, consisting of two protons and two neutrons, is also a common product of radioactive decay, where the nuclei are known as alpha particles.
RELATED ELEMENTS
3-SECOND BIOGRAPHIES
NORMAN LOCKYER
1836–1920
British astronomer who discovered helium’s spectral lines in the sun
WILLIAM RAMSAY
1852–1916
British chemist who isolated helium
30-SECOND TEXT
Brian Clegg
We know helium from the balloons that rise to the ceiling at parties, and helium airships were once the future of aviation. Norman Lockyer discovered the element.
During the 1890s, new technology used to liquefy air enabled the British chemist William Ramsay to separate out minor gaseous constituents whose existence had hardly been suspected. He isolated five new chemical elements now known as noble gases, including neon, which constitutes about one part in 60,000 of air. This remarkable achievement earned him the Nobel Prize in Chemistry in 1904. Ramsay confirmed that these gases were, indeed, unique elements by examining the characteristic spectrum of light they produce when excited by an electric discharge. His co-worker, fellow British chemist Morris Travers, was thrilled to note a ‘blaze of crimson light’ in the case of neon. Neon is so inert that it forms no chemical compounds at all. Yet, despite this lack of reactivity, it is one of the elements most widely known outside the laboratory – because of this signature light. The light is produced when electrons in orbit around the nuclei of neon atoms, having been excited by the electric discharge, return to their normal positions, releasing the energy they have absorbed. In the modern era, ‘neon’ has become a byword for all kinds of illuminated messages, although neon itself only produces red light. Other inert gases yield other colours when they are similarly placed in an electric discharge.
3-SECOND STATE
Chemical symbol: Ne
Atomic number: 10
Named: From Greek neon (‘new’)
3-MINUTE REACTION
One of the lightest and chemically most stable of the elements, neon is the fifth most abundant element in the universe – after hydrogen, helium, oxygen and carbon. It is a product of the alpha process, in which heavy elements are formed by the addition of alpha particles or helium nuclei to lighter atoms. Helium nuclei contain four nucleons (two protons and two neutrons), while carbon, oxygen and neon contain 12, 16 and 20 nucleons respectively.
RELATED ELEMENTS
3-SECOND BIOGRAPHIES
DMITRI MENDELEEV
1834–1907
Russian chemist who resisted extending the periodic table to accommodate Ramsay’s new elements
GEORGES CLAUDE
1870–1960
French innovator of neon signs
BRUCE NAUMAN
1941–
American artist who often works with neon
30-SECOND TEXT
Hugh Aldersey-Williams
Bright neon lights do not obscure William Ramsay, discoverer of neon and other noble gases.
Argon is all around us – there are about 50 trillion tons of it in the atmosphere – yet we didn’t catch up with it until the late 19th century. That’s because argon doesn’t do anything to make itself known. Like the other elements that share its column in the periodic table, it is an inert gas: unreactive, if not downright lazy (the quality for which it’s named). Argon does not lose or share any electrons by undergoing chemical reactions; it has a so-called filled shell of electrons. It was discovered in studies of the composition of air, of which it makes up 1 per cent. British chemist Henry Cavendish noticed an inert fraction of air in 1785, but didn’t follow it up, and not until 1894 did his compatriots Lord Rayleigh and William Ramsay isolate the inert component from atmospheric nitrogen. Today, three quarters of a million tons of argon are extracted annually from liquefied air, because its very inertness makes it useful. You can fill light bulbs, fluorescent tubes and double-glazed windows with it, or use it as a propellant for aerosols, industrial sprays and even futuristic ion-propulsion spacecraft engines, without worrying that it will react or be toxic.
3-SECOND STATE
Chemical symbol: Ar
Atomic number: 18
Named: From Greek argos (‘lazy, inactive’)
3-MINUTE REACTION
It is possible to make argon react with other elements, but only just. In 2000, a team from the University of Helsinki reported that they had reacted argon with hydrogen fluoride in a matrix of solid, frozen argon at a temperature of –246°C (–411°F). The result was argon fluorohydride, chemical formula HArF – but you can barely so much as look at it without it decomposing.
RELATED ELEMENTS
3-SECOND BIOGRAPHIES
HENRY CAVENDISH
1731–1810
British chemist who identified first hint of argon in 1785
JOHN STRUTT (LORD RAYLEIGH) & WILLIAM RAMSAY
1842–1919 & 1852–1916
British chemists, co-discoverers of argon in 1894
30-SECOND TEXT
Philip Ball
Argon was difficult to isolate – Lord Rayleigh declared it cost ‘a thousand times its weight in gold’ – but it has many modern uses and today is produced in vast quantities.
