absolute zero –273.15°C (–459.67°F), extrapolated temperature at which atoms have reached so low a kinetic energy that they have almost completely ceased moving.
allotropes Different forms of an element that exist in the same physical state. For example, diamond is an allotrope of carbon.
daughter isotope The product of radioactive decay of an isotope. The original (pre-decay) isotope is called the ‘parent isotope’.
ion exchange chromatography Process for separating molecules in a compound on the basis of their charge.
kelvin Temperature scale developed by British chemist William Thomson, Lord Kelvin (1824–1907) in 1848 that takes absolute zero as its starting point. A degree on the scale is equivalent to 1 degree on the Celsius scale, but 0 Kelvin = –273.15°C (–459.67°F). Boiling point for water (100°C/212°F) is therefore 373.15K, and water’s freezing point (0°C/32°F) is 273.15K.
nuclear fission The splitting of an atomic nucleus, releasing energy. This process is used in nuclear power stations and some nuclear bombs. Isotopes of uranium and plutonium (uranium-235 and plutonium-239) are usually used as fuel. A neutron fired at a uranium-235 atom splits the nucleus, forming two smaller nuclei, releasing energy and liberating three neutrons. These neutrons hit other uranium-235 nuclei and the process continues in a ‘chain reaction’. In a reactor, the reaction has to be controlled to prevent an explosion. The bombs dropped on the Japanese cities of Hiroshima and Nagasaki in the Second World War were both fission bombs, using uranium (Hiroshima) and plutonium (Nagasaki).
nuclear fusion The joining together (fusing) of atomic nuclei to form a single larger nucleus. As with nuclear fission, the process of fusion releases large amounts of energy. Nuclear fusion powers active stars. In our sun, hydrogen nuclei fuse to form helium. The United States produced one bomb powered by nuclear fusion, under the code name ‘Ivy Mike’, exploded in a test on the Enewetak Atoll, Pacific Ocean, on 1 November 1952.
transuranic element An artificial element with more protons (a higher atomic number) than uranium (which has 92).
trivalent ion An ion with a valency of three.
valency Measure of an atom’s combining power, the number of bonds an atom of an element can form with other atoms.
LANTHANIDES (RARE EARTHS) AND ACTINIDES
The lanthanides is a group of elements originally discovered in infrequently found minerals and therefore called ‘rare earth elements’; because the elements are found more widely than was once thought, the ‘rare earth’ label has been dropped from correct usage and the elements are known – as here – as the lanthanides. The lanthanides and actinides occupy the two blocks laid out beneath the periodic table in the conventional layout of the table. Both groups are metallic chemical elements. All lanthanides, aside from promethium, are non-radioactive; actinides are all radioactive.
Lanthanides
|
Symbol |
Atomic Number |
Lanthanum |
La |
57 |
Cerium |
Ce |
58 |
Praseodymium |
Pr |
59 |
Neodymium |
Nd |
60 |
Promethium |
Pm |
61 |
Samarium |
Sm |
62 |
Europium |
Eu |
63 |
Gadolinium |
Gd |
64 |
Terbium |
Tb |
65 |
Dysprosium |
Dy |
66 |
Holmium |
Ho |
67 |
Erbium |
Er |
68 |
Thulium |
Tm |
69 |
Ytterbium |
Yb |
70 |
Actinides
|
Symbol |
Atomic Number |
Actinium |
Ac |
89 |
Thorium |
Th |
90 |
Protactinium |
Pa |
91 |
Uranium |
U |
92 |
Neptunium |
Np |
93 |
Plutonium |
Pu |
94 |
Americium |
Am |
95 |
Curium |
Cm |
96 |
Berkelium |
Bk |
97 |
Californium |
Cf |
98 |
Einsteinium |
Es |
99 |
Fermium |
Fm |
100 |
Mendelevium |
Md |
101 |
Nobelium |
No |
102 |
The discovery of element 61 represented the filling of the final gap within the old limits of the periodic table and was achieved following the discovery of ion-exchange chromatography in the Manhattan Project during the Second World War. The classical methods of separation had failed to discover element 61 because there is simply not enough of the element in the earth’s crust. The researchers who synthesized the element in 1945 were not deliberately setting out to form it. The new element, which was eventually called promethium, was identified in the course of attempts to characterize isotopes produced by radiation experiments. Promethium is unusually unstable, and the only one of the 14 lanthanides that is radioactive. Contrary to many published accounts, promethium does occur naturally on earth in minuscule amounts in the mineral apatite and in pitchblende. The isotope Pm-147 is used in nuclear batteries because it is a medium emitter of beta particles that does not produce too much undesirable secondary radiation. Nuclear batteries are expensive, but they tend to have half-lives of as much as 10–20 years, making them much longer-lasting than conventional chemically based batteries. They provide excellent power sources for spacecraft, hearing aids and heart pacemakers.
3-SECOND STATE
Chemical symbol: Pm
Atomic number: 61
Named: From Prometheus, the character in ancient Greek mythology who stole fire from the gods
3-MINUTE REACTION
Until recently, the promethium-based batteries used in space and military applications were large, but a team from the University of Missouri in the United States has now produced batteries the size of a penny and is aiming to reduce the thickness of such batteries to the thickness of a human hair. Such batteries hold up to one million times the charge of a conventional battery.
RELATED ELEMENTS
3-SECOND BIOGRAPHIES
HENRY MOSELEY
1887–1915
English physicist who confirmed that element 61 was missing
JACOB MARINSKY & LAWRENCE GLENDENIN
1918–2005 & 1918–2008
American chemists, co-discoverers of promethium
30-SECOND TEXT
Eric Scerri
Promethium batteries are ideal in cases when it is desirable not to have to change the batteries very often – for example, in heart pacemakers or on board space vehicles.
The rare earth metal europium is a lanthanide, one of the collection of elements that fits between barium and lutetium on the periodic table. The label ‘rare earth’ is out of date – the rare earths were originally discovered in scarce minerals, but they occur more widely than was first thought. Although a metal, europium is never found naturally in its shiny silvery state because it reacts so easily with the air or water. Europium had three different discoverers. In the late 1880s, British chemist William Crookes found a new spectral line in a mineral that would later be identified as belonging to europium – he was the first to discover the existence of the element. Soon after, French chemist Paul Lecoq de Boisbaudran separated off a material that had the distinctive europium spectral lines, and finally in 1901 another French scientist, Eugene-Anatole Demarçay, isolated a specific europium salt, for which he is usually given the honour of being europium’s discoverer. Europium’s main practical role is in phosphors (materials that glow when stimulated by electrons or ultraviolet), but it is also excellent at absorbing stray neutrons, and though it has yet to be widely used, it could be valuable in this role to help control nuclear reactors.
3-SECOND STATE
Chemical symbol: Eu
Atomic number: 63
Named: For the continent of Europe
3-MINUTE REACTION
Europium is a versatile doping agent for phosphors. Doping involves adding a small amount of impurity to give a specific colour to the glow produced in phosphors by ultraviolet or electrons. The word ‘fluorescent’ comes from the mineral fluorite, which has a blue glow thanks to europium salts with valency 2; fluorite is also used in fluorescent tubes, where it is combined with valency 3 europium salts.
RELATED ELEMENTS
3-SECOND BIOGRAPHIES
WILLIAM CROOKES
1832–1919
British chemist who discovered europium’s spectroscopic trace
EUGENE-ANATOLE DEMARÇAY
1852–1904
French chemist who isolated the first europium salt
30-SECOND TEXT
Brian Clegg
Several chemists have had to share credit for discovering europium, the most volatile of the lanthanide elements. Aside from its role as a dopant for phosphors, it is often used in research.
Gadolinium has an unusual trait shared only by the transition metals iron, cobalt and nickel: ferromagnetism. (This is the mechanism by which certain materials form permanent magnets when placed in a magnetic field; the materials become magnetic and remain so after the external magnetic field is removed.) Gadolinium is a stronger ferromagnet than these three other naturally occurring elements—but only when supercooled to 0 Kelvin (–273.15°C/–459.67°F). When not supercool, gadolinium is ferromagnetic below and paramagnetic above 20°C (68°F); this suggests applications as a magnetic component that can sense hot and cold. (Paramagnetic materials are attracted by a magnetic field but do not retain magnetic properties when the field is removed.) Gadolinium is used in nuclear reactor control rods because it has the highest known capability to absorb neutrons of any natural isotope of any element. Gadolinium gallium garnets and gadolinium yttrium garnets are manufactured for use in microwave applications and in fabrication of various optical components. Found in association with other lanthanides in many minerals, gadolinium occurs in nature in its salts and especially as the oxide, gadolinia, for which it was named.
3-SECOND STATE
Chemical symbol: Gd
Atomic number: 64
Named: For gadolinite, named after Johan Gadolin (1760–1852), who also discovered yttrium
3-MINUTE REACTION
Naturally occurring gadolinium is composed of six stable isotopes and one radioactive isotope, with Gd-158 being the most abundant. Unlike other rare earth elements, metallic gadolinium is relatively stable in dry air. Like most rare earths, gadolinium forms trivalent ions that have fluorescent properties, making gadolinium compound useful as green phosphors in consumer electronics. Gadolinium as a phosphor is also used in other imaging functions such as in X-ray systems.
RELATED ELEMENTS
3-SECOND BIOGRAPHIES
JEAN CHARLES GALISSARD DE MARIGNAC
1817–94
Swiss chemist who studied the rare earth elements, leading to his discovery of ytterbium and co-discovery of gadolinium
PAUL ÉMILE LECOQ DE BOISBAUDRAN
1838–1912
French chemist who isolated gadolinium in 1886
30-SECOND TEXT
Jeffrey Owen Moran
Gadolinium is useful in magnetic resonance imaging (MRI), as well as in X-rays – and it is added to iron, chromium and related alloys to make them easier to work.
Protactinium was one of the few missing elements predicted by Russian chemist Dmitri Mendeleev that was not isolated until well into the 20th century. Mendeleev called it ‘eka-tantalum’; he claimed that it should form an oxide with formula R2O5, like the elements in the same column of the periodic table, niobium and tantalum. It does – he was right. The first hint of eka-tantalum came from the British chemist-inventor William Crookes, who failed to extract it but identified a new substance that he dubbed ‘uranium-X’ in uranium ores. In 1913, Polish-American chemist Kazimierz Fajans and his German colleague Oswald Göhring identified an isotope of element 91 and named it brevium in view of its short half-life of 1.17 minutes. Strictly speaking, this represents the first true discovery of the element; however, credit usually goes to the isolation of the longest-lived isotope of a new element, and this was discovered in 1917 by Austrian-Swedish physicist Lise Meitner and German chemist Otto Hahn. Their isotope has a vastly longer half-life of 32,500 years and was named proto-actinium, later shortened to protactinium, meaning the element that forms actinium (element 89) when it loses an alpha particle. The element has virtually no applications due to the fact that it is extremely rare, toxic and highly radioactive.
3-SECOND STATE
Chemical symbol: Pa
Atomic number: 91
Named: A slight abbreviation of proto-actinium, meaning ‘the element that produces actinium’, which it does by alpha decay
3-MINUTE REACTION
Between 1959 and 1961, the UK Atomic Energy Commission succeeded in isolating about 125 g (43/8 oz) of protactinium, starting from 60 tons of raw uranium ores. This remains as the largest stash of the element, although it has been somewhat depleted after samples have been sent to scientific establishments around the world.
RELATED ELEMENTS
3-SECOND BIOGRAPHIES
WILLIAM CROOKES
1832–1919
English scientist, journal editor, photographer and inventor
KAZIMIERZ FAJANS
1887–1975
Polish-American radiochemist, discoverer of brevium, a short-lived isotope of element 91
FREDERICK SODDY
1877–1956
English radiochemist who discovered protactinium
30-SECOND TEXT
Eric Scerri
Otto Hahn and Lise Meitner were discoverers of the longest-lived isotope (protactinium-231) of this highly radioactive, silvery-grey metal.
People used to eat off uranium, and some still do. The element was discovered in the mineral pitchblende in 1789, and in the 19th century it was used to make a bright orange glaze for tableware and a colouring agent for green glass. Orange uranium-ware was still being made in the 1940s, albeit using less radioactive ‘depleted uranium’, whilst at that same time uranium was being processed by the Manhattan Project into the nuclear bomb that destroyed Hiroshima, Japan, in 1945. The radioactivity of uranium was discovered in 1896 by French scientist Henri Becquerel, who found, while investigating X-rays, that uranium compounds emit a new type of ‘ray’. It became clear that the energy leaking from uranium in this way was enormous, and that it was coming from the atomic nuclei. In 1938, German chemists Otto Hahn and Fritz Strassmann in Berlin – together with the Austrian physicist Lise Meitner – found that a uranium nucleus may split in half (undergo fission) when it absorbs a neutron, raising the possibility of a sustained uranium chain reaction that could liberate its nuclear energy more quickly. In a nuclear reactor, the chain reaction is controlled; in a bomb, it becomes a runaway process, releasing the nuclear energy in an explosion.
3-SECOND STATE
Chemical symbol: U
Atomic number: 92
Named: After Uranus, the planet discovered eight years before uranium
3-MINUTE REACTION
Uranium has several isotopes, all of them radioactive. However, only one uranium isotope, denoted U-235, undergoes easier nuclear fission, whereas more than 99 per cent of natural uranium is the barely fissile isotope U-238. So making a bomb demanded that the U-235 be concentrated – a slow process because the isotopes are chemically identical and can’t easily be separated. Depleted uranium has some U-235 removed because it is more radioactive (it decays faster).
RELATED ELEMENTS
3-SECOND BIOGRAPHIES
MARTIN KLAPROTH
(1743–1817)
German chemist who discovered uranium in 1789
HENRI BECQUEREL
(1852–1908)
French physicist who discovered radioactivity (‘uranic rays’) in uranium
LISE MEITNER
(1878–1968)
Austrian physicist who realized that uranium could undergo nuclear fission
30-SECOND TEXT
Philip Ball
The same element once used to colour earthernware and glassware powered the ‘Little Boy’ bomb that devastated Hiroshima on 6 August 1945.
Glenn T. Seaborg was one of the most important chemists of the 20th century. His discoveries had the greatest impact on the periodic table since Russian chemist Dmitri Mendeleev first proposed the concept in the late 1860s. Seaborg co-discovered and manufactured plutonium and nine other elements among the transuranium elements. He also defined a new set of elements on the periodic table, the actinides.
Seaborg was born in Michigan, 1912, into a family of Swedish immigrants. He studied chemistry at the University of California, Los Angeles, before achieving his doctorate at UCL Berkeley in 1937. He spent most of his career at Berkeley, where he became a professor of chemistry and eventually chancellor. He made his key discoveries using the university’s Lawrence Cyclotron.
In 1941, Seaborg co-discovered the element plutonium, with Edwin McMillan, Joseph Kennedy and Arthur Wahl. Plutonium would be used in nuclear reactors and in the atomic bomb dropped on Nagasaki – which Seaborg also helped to develop. During the war, he joined a number of scientists who petitioned US President Truman to stage a public demonstration of the atomic bomb’s might, to persuade Japan to surrender. However, their request fell on deaf ears.
In 1940, Edwin McMillan discovered neptunium and over the next 16 years Seaborg and his co-workers at Berkeley discovered the other nine elements in the transuranium sequence, from neptunium (number 93) to nobelium (number 102) – all heavier than uranium.
In 1944, Seaborg inferred that the 14 elements heavier than actinium shared similarities with the element itself and belonged in their own family (the actinides). This sequence included the transuranic elements and showed where they fitted in the table. His theory involved a major redrawing of the periodic table into its current form, with the actinide series running as a strip below the lanthanide series. Seaborg’s achievements won him the Nobel Prize for Chemistry in 1951, which he shared with Edwin McMillan.
Seaborg spent years researching nuclear medicine, discovering radioactive isotopes including iodine-131, which enabled his own mother to make a full recovery from thyroid disease. He also advised ten US presidents on atomic energy. Controversially, he was the only scientist to have an element publicly named after him during his lifetime – seaborgium. He remarked that it was ‘the greatest honour ever bestowed upon me’.
Born in Ishpeming, Michigan
1937
Achieves his doctorate in chemistry from University of California, Berkeley
1937–46
Researches and teaches at UCL Berkeley; appointed professor in 1945
1941
Co-discovers plutonium, with Edwin McMillan, Joseph Kennedy and Arthur Wahl
1942
Joins the Manhattan Project
1944–58
Leads a team that discovers the following elements:
1944: curium and americium
1949: berkelium
1950: californium
1952: einsteinium and fermium
1955: mendelevium
1958: nobelium
1951
Awarded the Nobel Prize for Chemistry
1958–61
Serves as chancellor of the University of California, Berkeley
1961–71
Chairman of the Atomic Energy Commission
1997
Makes history as the first living scientist to have an element named after him – seaborgium
25 February 1999
Dies in Lafayette, California, following a stroke
You may see the actinide metal plutonium described as the most poisonous substance in existence, but while the element is without doubt poisonous if ingested or inhaled, several natural toxins are more deadly, and in any case, it would be difficult in practice to use plutonium to cause mass poisoning. From its discovery, plutonium has been considered a significant rival to uranium for nuclear energy and the production of nuclear bombs. It is difficult to get a sufficient quantity of plutonium into a critical mass all at the same time, yet if this is achieved 8 kg (18 pounds) of plutonium-239 is enough to produce the damage caused in 1945 by the plutonium bomb dropped at Nagasaki, Japan. Some sources identify uranium as the heaviest of the natural elements, and report that transuranic elements such as plutonium are artificial. However, plutonium does exist in nature: like all the elements heavier than iron, it is created in supernova explosions. We don’t see much plutonium on the earth because during the 4.5 billion years of the earth’s existence, almost all of our natural plutonium, with the longest half-life at around 80 million years for plutonium-244, has undergone radioactive decay to form uranium.
3-SECOND STATE
Chemical symbol: Pu
Atomic number: 94
Named: After the dwarf planet Pluto
3-MINUTE REACTION
Plutonium comes in six allotropes (physical structural variants); it is chemically rich in compounds because it has five oxidation states. This silvery metal, which rapidly oxidizes to a grey sheen, can be used when combined with cobalt and gallium to produce a relatively high-temperature superconductor at around 18.5 Kelvin (–254.65°C/– 426.37°F), although its superconducting state is disrupted as the plutonium decays.
RELATED ELEMENTS
3-SECOND BIOGRAPHIES
EDWIN MCMILLAN
1907–91
American physicist, first to create a transuranic element (neptunium, in 1940)
GLENN T. SEABORG
1912–99
American chemist who discovered plutonium at Berkeley in 1940
30-SECOND TEXT
Brian Clegg
Created in supernova explosions in distant space, and the power behind the ‘Fat Man’ bomb detonated over Nagasaki, Japan, on 9 August 1945, plutonium is found on earth in tiny amounts in uranium ores.
