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ELEMENTOLOGY:
BASICS ABOUT PERIODIC TABLE OF ELEMENTS!!!
periodic table, an arrangement of the chemical elements in order of increasing atomic number--that is, the number of protons
in their nuclei. In the traditional form of the table the elements were arranged horizontally in seven rows called periods;
the first period consisted of two elements (hydrogen and helium), the second of eight elements (lithium to neon), the third
of eight elements (sodium to argon), the fourth of eighteen (potassium to krypton), and so on. In this form of the table,
it was customary to divide the main groups into subgroups A and B. These were numbered from IA to VIIA and from IB to VIIB
with Group 0 for the noble gases. The transition elements were placed in a block in the centre of the table. There was considerable
confusion about the numbering of groups, in particular the designation of which sets of elements belong to A or B subgroups.
Consequently, it was decided to number the groups across the table from Group 1 to Group 18. Atoms which form positive ions
are represented to the left of each period, and the electronegative ones to the right. When the elements are arranged in this
way, they fall into columns called periodic groups; and it is found that elements occurring in the same group resemble each
other chemically: thus all the noble gases appear in the extreme right-hand group, which is called Group 0. This pattern occurs
because the properties of an element depend primarily on the number of electrons in its outermost (valence) shell. Each shell
can only hold a fixed number of electrons. When the shell becomes full, a new shell is started and a new period in the table
is begun. The table's arrangement therefore reveals information on the electronic configuration of atoms. The periodic table
was originally suggested by Dimitri Mendeleyev and was used to predict undiscovered elements; the existence of germanium was
predicted when it became clear that there must be an unknown element between gallium and arsenic, if subsequent elements were
to fit into the appropriate groups in the table
lithium (symbol Li, at. no. 3, r.a.m. 6.94), a soft, metallic element in Group 1 (formerly IA) of the periodic table,
the alkali metals. It is obtained by the electrolysis of a fused mixture of potassium and lithium chlorides. Lithium is reactive,
and is stored under oil; it combines with non-metals, water, and acids, forming ionic compounds in which it has the charge
+1, and a few covalent compounds. Lithium carbonate is used in glasses and ceramics, and as a tranquillizer in manic depression;
lithium hydride is used as a source of hydrogen, and lithium hydroxide is used to absorb carbon dioxide in submarines. Lithium
salts of fatty acids are widely used in lubricating oils as thickeners. The isotope lithium-6 forms tritium when bombarded
with neutrons.
potassium (symbol K, at. no. 19, r.a.m. 39.10), an alkali metal element, similar in properties to sodium, obtained either
by the electrolysis of molten potassium chloride or by the reaction of metallic sodium with molten potassium chloride. Potassium
tarnishes quickly in air and reacts violently with water, producing a lilac flame, and so is stored under paraffin to avoid
contact with water vapour. Potassium is produced on a small scale only, offering few advantages over the much cheaper sodium.
Compounds of potassium are important as fertilizers, in the production of soft soaps, in the manufacture of gunpowder and
photographic chemicals, and in extracting gold and silver from their ores. When it is alloyed with sodium, the molten mixture
has a high specific heat which makes it useful as a coolant in nuclear reactors.
caesium (US, cesium, symbol Cs, at. no. 55, r.a.m. 132.91), a soft silvery metallic element, one of the alkali metals.
It reacts vigorously with non-metals and water; and its compounds closely resemble potassium compounds. It is used in photoelectric
cells and in the caesium atomic clock.
magnesium (symbol Mg, at. no. 12, r.a.m. 24.31), a grey metallic element of low density in Group 2 (formerly IIB) of the
periodic table, the alkaline earth metals. Reacting readily with acids and non-metals, it forms ionic compounds in which it
has charge +2. It is an abundant element: magnesium chloride is present in seawater, from which magnesium is obtained by electrolysis,
and magnesium ores such as dolomite, talc, and asbestos are widespread. Magnesium is also used in flash-bulbs and flares,
as it gives an intense white light when it reacts with oxygen. Because of its low density it is also widely used as a component
of lightweight, strong alloys in the die casting or extrusion of articles such as luggage frames, ladders, pistons, crankcases,
car and motor-cycle wheels, airframes, and propellers. The pure metal is soft, and has to be strengthened by alloying with
aluminium, zinc, zirconium, and thorium. Important compounds of magnesium include magnesium hydroxide (Mg(OH)2), used as an
antacid and laxative, magnesium sulphate (Epsom salts, MgSO4), and Grignard reagents, used in synthetic organic chemistry.
lead (symbol Pb, at. no. 82, r.a.m. 207.2), a soft, dense, grey metal which occurs in Group 14 (formerly IVB) of the periodic
table. The principal ore is lead sulphide (PbS), commonly called galena, which is mined extensively in the USA. Lead oxide
is obtained by roasting the ore, which is then reduced to lead by heating in a blast-furnace with coke and scrap iron. It
can be further refined by electrolysis. Chemically, lead is an unreactive element; it dissolves slowly in nitric acid but
resists other acids, water, and oxygen. In its compounds it shows the valencies 2 and 4. Because it is cheap and corrosion-resistant,
it has been employed widely for roofing and for protecting cables and pipes underground; and as it absorbs radiation, it is
used to shield X-ray equipment and nuclear reactors. It is also made use of in storage batteries, as ammunition, and in low-melting
alloys such as solder and pewter--but not in pencils, the 'lead' in which is a mixture of graphite and clay. Tetraethyl lead,
Pb(C2H5)4, is extensively used as an anti-knock additive in petrol, although like all other lead compounds it is toxic, and
it has been suggested that its use may be a significant health hazard. Lead carbonate and lead chromate are used as paint
pigments, and paints containing red lead oxide are effective rust inhibitors. Four lead isotopes occur naturally: 204Pb, 206Pb,
207Pb, and 208Pb. Each is the end-product of a radioactive decay chain. The isotopic composition of lead therefore varies
from place to place, and the relative atomic mass of lead is not constant.
selenium (symbol Se, at. no. 34, r.a.m. 78.96), a metalloid element in Group 16 (formerly VIB) of the periodic table;
it occurs in several different allotropes including a metallic form. It occurs as an impurity in sulphide ores, from which
it can be recovered. The stable, grey selenium allotrope contains chains of selenium atoms whose conductivity is increased
by light; it is used as a photoconductor in photoelectric cells (see photoelectric effects). It is also used in photocopiers
and alternating-current rectifiers, in colouring glass red, in ceramic glazes, and in hardening steel. It is an essential
trace element and is present in some garlic-smelling plants.
radium (symbol Ra, at. no. 88, r.a.m. 226.03), a rare, white, radioactive element discovered by Marie and Pierre Curie
in 1898 in the mineral pitchblende, which is the chief ore. The last member of the alkaline earths, it reacts with water and
tarnishes in air. It has several isotopes which are members of radioactive decay sequences, the most stable, radium-226, having
a half-life of 1,620 years before decaying to the gas radon. The discovery of radium led to numerous crucial experiments on
radioactivity, paving the way for the rapid advances in atomic physics in the 20th century. Until the 1920s radium was used
in radiotherapy.
aluminium (US, aluminum: symbol Al, at. no. 13, r.a.m. 26.98), a soft metallic element in Group 3 (formerly IIIA) of the
periodic table, which in air has a thin, unreactive, and strongly adherent oxide coating that protects it from corrosion.
This protects the metal from further oxidation and accounts for its apparently low reactivity. Articles made of aluminium
can be coloured and given additional resistance to wear by anodizing. Aluminium is an excellent conductor of heat. This property,
together with its resistance to corrosion and its low density, explains why it is used for cooking utensils and foil and,
increasingly, in the canning industry. It is also a good conductor of electricity and is widely used in overhead cables. Aluminium
powder is used in paints and in the thermite reaction (see welding). Alloys of aluminium, such as duralumin, have high tensile
strengths and are of considerable industrial importance, particularly in the aerospace industry. The most important ore is
the hydrated oxide, bauxite (approximately Al2O3-2H2O). This is dissolved in hot sodium hydroxide, precipitated, and heated
to form alumina. Alumina is then reduced to aluminium by an electrolytic process developed by Hall and Heroult. Some aluminium
compounds are important: aluminium chloride is used as a catalyst in organic chemistry and for cracking petroleum; alum is
used in the purification of water and as a mordant for dyes.
boron (symbol B, at. no. 5, r.a.m. 10.81), a yellow-brown, non-metallic element of Group 3 (formerly IIIB) of the periodic
table. It occurs as the ore orthoboric acid B(OH)3 and as borates such as borax. Pure boron is produced from the oxide B2O3
by reaction with magnesium followed by chlorination and reduction with hydrogen. Crystalline boron is transparent, brittle,
a non-conductor, and nearly as hard as diamond. Treating the surface of steel with boron makes it very hard. The boron-10
isotope is used in the control rods of nuclear reactors because it is a strong neutron absorber. Chemically, boron does not
resemble the other Group 3 elements closely; it reacts with the halogens, concentrated acids, and oxygen, forming covalent
compounds. Its most important compounds are the borates, which are derived from boric oxide (B2O3); they are used in glasses,
enamels, and glazes. Sodium borohydride (NaBH4) is an important reducing agent in organic chemistry.
beryllium (symbol Be, at. no. 4, r.a.m. 9.01), a grey, light metallic element in Group 2 (formerly IIA) of the periodic
table. The element is usually obtained by electrolysis of a fused mixture of beryllium fluoride and sodium fluoride. It reacts
with acids and alkalis, showing valency 2 in its compounds, but is resistant to oxidation because of the formation of a protective
oxide layer. It is used in certain beryllium-copper alloys, which have a range of uses depending on their strength, corrosion
resistance, and electrical and thermal conductivity. The pure metal transmits X-rays because of its low atomic number and
is used for windows in X-ray tubes. Beryllium metal dust and beryllium compounds are highly toxic, causing lung diseases and
dermatitis.
carbon (symbol C, at. no. 6, r.a.m. 12.01), a non-metallic element in Group IV of the periodic table. It exists in three
allotropes: diamond is extremely hard, colourless, and an insulator; graphite is a soft, black solid which conducts heat and
electricity; buckminsterfullerene is a yellow crystalline compound containing C60 molecules. Coke, produced by the destructive
distillation of coal, is almost pure carbon, and charcoal is a form of carbon made from wood. Carbon fibres are long chains
of pure carbon formed by heat treatment of acrylic fibres. Although carbon is rather unreactive at low temperatures, on heating
it reacts with oxygen, sulphur, and some metals. Carbon atoms can bond together in chains and rings, and carbon forms more
compounds than any other element. Because many of them were first discovered in living organisms, their chemistry is called
organic chemistry, but there is no fundamental distinction between organic and other compounds. All life forms are based on
carbon chemistry. Diamonds are used as jewellery and for cutting and grinding; graphite is used as a lubricant, in pencil
leads, in nuclear reactors and as electrodes. Charcoal is used to absorb gases, as a decolorizer, and in paints and gunpowder;
coal and coke consist mainly of carbon, and are important fuels. Carbon has a radioactive isotope, carbon-14, which is formed
in the upper atmosphere from nitrogen and then incorporated into living things; radiocarbon (or carbon) dating is based on
the decay of the carbon-14 isotope after the death of an animal or plant (see radiometric dating). Carbon forms two common
oxides: carbon dioxide and carbon monoxide.
tin (symbol Sn, at. no. 50, r.a.m. 118.69), a metal in Group 14 (formerly IVB) of the periodic table which occurs as three
allotropes. The ordinary 'white tin', b-Sn, is malleable and ductile, and when a bar of tin is bent, a distinctive 'tin cry'
is heard as the crystal structure breaks. Below 13 oC (55 oF) 'grey tin', a-Sn, is the stable form, but the change from white
tin into grey tin takes place only at much lower temperatures unless some grey tin is already present. When the change does
occur the tin crumbles into a powder, and this is called 'tin plague' or 'tin pest'. The presence of impurities in commercial
tin normally prevents this happening. Above 161 oC (342 oF), it exists as the brittle g-Sn. The major ore is cassiterite,
SnO2, which after some initial purification is reduced by smelting with carbon to form the metal. Tin is refined by re-heating
just to melting-point in a furnace with an inclined hearth; the purer tin flows down the slope, leaving impurities in the
dross. It can be further purified by electrolysis. The main use of tin is in the production of tin plate. Tin plate is used
in the manufacture of a wide variety of cans and utensils, although many of these are now made from aluminium or from polymer-based
products. Most tin plate is now produced by electroplating, which requires less tin than the original process of dipping the
sheet in molten metal, and gives a better coating. Tin is also used in the production of various alloys, such as solder, bronze,
and type metal. Some alloys with niobium exhibit superconductivity. Tin compounds are used in the manufacture of opaque glasses
and enamels, and as mordants in dyeing. Tin fluoride (SnF2) is the additive in fluoride tooth-pastes, Tin(II) chloride, SnCl2,
the most important compound, is used as a reducing agent and as a mordant in dyeing. Chemically, tin exhibits valencies of
2 and 4. It resists attack by water but is dissolved by strong acids and alkalis.
nitrogen (symbol N, at. no. 7, r.a.m. 14.01), a colourless, odourless gas which makes up about 78 per cent of the Earth's
atmosphere by volume. In its free state it consists of diatomic molecules, N2. It is produced on a large scale by the fractional
distillation of liquid air, having a lower boiling point (-196 oC, -385 oF) than air's other main component, oxygen. It is
an extremely unreactive element, forming metal nitrides only at high temperatures; even so, it forms a wide range of compounds
which are of vast importance, for example in photography, and as dyestuffs, explosives, and polymers. It is used in the manufacture
of ammonia and nitric acid, and also where an inert atmosphere is required. Liquid nitrogen is an important coolant. Nitrogen
is an essential element for all life-forms: plants use it to build amino acids, proteins, and enzymes, and ammonium compounds
and nitrates are therefore widely used as fertilizers. Some bacteria can convert nitrogen gas directly from the atmosphere
into nitrogen compounds; this process is called nitrogen fixation (see nitrogen cycle). Large quantities are used to produce
ammonia by the Haber-Bosch process.
oxygen (symbol O, at. no. 8, r.a.m. 15.9994), a colourless, odourless gas, and the most abundant element on Earth, occurring
in the crust, in fresh water and sea-water, and in the atmosphere, of which it forms 21 per cent by volume. Oxygen belongs
to Group 16 (formerly VIB) of the periodic table. It exists both as the highly reactive molecule O2 and, especially in the
upper atmosphere, as the even more reactive O3, or ozone. As the element involved in respiration and a product of photosynthesis,
it is essential to most forms of life. Oxygen is slightly denser than air and has a boiling-point of -183 oC (-361 oF). It
is manufactured by the fractional distillation of liquid air, from which the nitrogen content is distilled first. Industrially
it has many uses, such as in welding, metal-cutting, explosives, and rocket fuels. It is necessary for combustion and will
relight a glowing splint, a simple laboratory test for oxygen. As an oxidizing agent it combines with all other elements,
except the noble gases, and with many compounds.
silicon (symbol Si, at. no. 14, r.a.m. 28.09), a browny-black metalloid element in Group 14 (formerly IVB) of the periodic
table. The element has a giant molecular structure similar to that of diamond. It is the second most abundant element after
oxygen and forms nearly 28 per cent of the Earth's crust. It is found in a wide range of silicate minerals. Industrially it
is formed by the reduction of silica, SiO2, with carbon or calcium carbide, CaC2, in an electric furnace. When it is purified
further, it is used to manufacture silicon chips in electronics; and when very small quantities of boron or phosphorus are
added (doping), it is used as a semiconductor in transistors. Silicon forms stable compounds in which it shows a valency of
4. Silicon carbide (carborundum) crystals, SiC2, are almost as hard as diamonds and are manufactured as abrasives. Solutions
of silicates are obtained by reacting the element with alkalis. Synthetic polymers can be formed of silicon, carbon, hydrogen,
and oxygen; they are called silicones and are oily liquids, resins, or rubbery solids, widely used as waxes and water repellents.
sulphur (US, sulfur; symbol S, at. no. 16, r.a.m. 32.06), a yellow non-metallic element in Group 16 (formerly VIB) of
the periodic table that exists in two different allotropes, both of which are yellow. It occurs naturally both in the free
state and in sulphides and sulphates, and is found chiefly around hot springs, and in volcanic regions. Sedimentary deposits
are found in Texas and Louisiana, USA. It is extracted, sometimes from considerable depths, by melting with superheated steam;
the liquid sulphur collects in a pool and is then pumped to the surface almost chemically pure. This is the Frasch process.
It is also found in some natural gas as hydrogen sulphide, H2S, and in sedimentary rocks such as gypsum. In ancient times
sulphur was known as brimstone and was employed with its blue flame and odorous smell in religious ceremonies, in witchcraft,
and in sorcery. Today it is principally used in the production of sulphuric acid by the contact process. It is also used in
the vulcanization of rubber, in the manufacture of gunpowder, and to produce carbon disulphide, a valuable solvent. Sulphur
dioxide is a toxic gas formed when sulphur burns in air, which is used to bleach straw and wool. It is a major cause of air
pollution and acid rain. Hydrogen sulphide, an extremely toxic gas with a characteristic smell of bad eggs, is produced in
large amounts at petroleum refineries. Pollution is reduced by controlled burning, in which one-third is burned to sulphur
dioxide, which then reacts with the remaining two-thirds to produce water and sulphur.
tungsten (symbol W, at. no. 74, r.a.m. 183.85), a lustrous silvery white transition metal, taking its name from the Swedish
for 'heavy stone'. Also known as wolfram, it occurs naturally as wolframite, (Fe, Mn) WO4, together with traces of stolzite,
PbWO4, and scheelite, CaWO4. Important deposits occur in the USA, Russia, and China; commercially the metal is obtained by
reducing tungsten oxide, WO3, with hydrogen or carbon. It has the highest melting-point, 3,410 oC (6,170 oF), the lowest vapour
pressure, and above 1,000 oC (1,832 oF) the highest tensile strength of any metal. Moreover, it is very resistant to corrosion,
and is only slightly attacked by acids. Its main uses are in steel alloys, as filaments in light bulbs, in television and
X-ray tubes, and in tungsten carbide tips for drilling and cutting tools. Tungsten carbide is an extremely hard substance.
It is used as an abrasive and for the tips of masonry bits.
chromium (symbol Cr, at. no. 24, r.a.m. 52.00), a hard, silvery-white metallic element; it is one of the transition metals.
Chromium resists corrosion and this, along with its metallic lustre, is the reason for its use in the electroplating of iron
and copper objects such as automobile trim and plumbing fixtures. The main ore is chromite (FeCr2O4), and reduction by carbon
in an electric-arc furnace yields an alloy of iron and chrome which is used in making chromium and stainless steel. Chromium
steels are very hard and strong and are used for armour plating, bank vaults, safes, cutting tools, and automobile parts.
Its compounds are widely used as pigments; chromium oxide is green, and lead chromate yellow. Chromium salts are used for
tanning leather and as mordants for dyestuffs.
copper (in chemistry); symbol Cu, at. no. 29, r.a.m. 63.55), a reddish-yellow metallic element which is a good conductor
of heat and electricity, and is corrosion-resistant. It is ductile (capable of being drawn into a wire) and malleable (able
to be hammered or pressed without breaking). Copper is a member of the transition metals and forms ionic compounds in which
it shows valency 2, or more rarely 1. Rather an unreactive metal, it is unaffected by water and acids; on long exposure to
air it acquires a green protective layer of basic copper carbonate: verdigris. Copper is chiefly used for electrical wiring,
but also for tubes and pipes, cooking utensils, fermentation tanks, and sometimes as a roofing material. It can be combined
with other metals to form alloys such as brass, bronze, and coinage metals. Copper salts, which are poisonous, are used in
dyeing as mordants in dyeing; as fungicides, insecticides, and algicides; and in the production of pigments and plastics.
The chief copper ore is chalcopyrites (CuFeS2), but other ores are also important, and the free element is found naturally.
Low-grade sulphide ores are concentrated by ore flotation and then roasted with limestone to give a mixture of copper and
iron sulphides called matte. Air is blown through the molten matte in a converter, oxidizing the iron to form a slag; sulphur
is removed as SO2 gas, leaving metallic copper. Traces of copper oxide formed by the air blast are removed by stirring the
molten metal with poles of green wood, which provide reducing gases. The resulting copper requires purification by electrolysis.
Major producers include the USA, Russia, Zambia, Zaire, and Chile.
gold (symbol Au, at. no. 79, r.a.m. 196.97), a soft, yellow, metallic element, one of the transition metals. It is very
unreactive, though attacked by halogens and aqua regia. Occurring in nature as small particles of the free metal, in quartz
or in alluvium, it caused the 19th-century gold rushes in America and Australia; today it is produced mainly in Russia and
South Africa. Panning for gold in rivers has been superseded by hydraulic mining and deep mining. Gold is extracted from the
deposit by treatment with cyanide and displacement with zinc. It is further purified by electrolysis or treatment with nitric
and sulphuric acids. Its rarity, appearance, and lack of reactivity have led to gold being highly valued throughout history.
Its value is thought to be more stable than that of many currencies, and it is widely held as an investment. Another major
use is as jewellery; gold is the most ductile and malleable of metals; a piece weighing 1 g (0.035 ounces) can be drawn into
a wire more than 2.5 km (1.5 miles) in length. It is also easily beaten into ornaments which are attractive and do not tarnish.
A good conductor of heat and electricity, it is used widely in electronics. Pure gold is too soft for most applications and
is generally hardened by alloying it with copper or silver. The gold content of alloys is measured in carats, with 24 carats
corresponding to pure gold.
manganese (symbol Mn, at. no. 25, r.a.m. 54.94), a reddish-white, hard, brittle transition metal. It is quite reactive,
and in its compounds shows valencies from 2 to 7. It is extracted mainly from the ore pyrolusite, (MnO2), although also occurring
naturally on the sea-bed. Manganese is widely added to metals to improve their hardness and wear resistance. Manganese steels
contain about 12 per cent manganese, and are very tough, being used in railway lines and rock-crushers.
nickel (symbol Ni, at. no. 28, r.a.m. 58.71), a hard, grey-white, ferromagnetic metal and one of the transition metals.
It occurs naturally in pentlandite and pyrrhotite. The crude ore is roasted to give the oxide, which is then reduced to the
metal with carbon. Purification is carried out by electrolysis or the Mond process, during which it is converted to the volatile
nickel carbonyl, Ni(CO)4. The metal is hard, malleable, ductile, and resistant to corrosion, so is widely used to plate objects
made from steel and copper. It is also the constituent of many important alloys, such as stainless steel, nimonics, Monel
metal, permalloy, nickel silver, nichrome, and invar. Finely divided nickel is an important industrial catalyst. Chemically
nickel resembles iron and cobalt with a usual valency of 2.
iron (symbol Fe, at. no. 26, r.a.m. 55.85), a silvery-grey ferromagnetic transition metal. Iron is a strong, malleable,
ductile metal, which is a good conductor of heat and electricity, but its properties are affected by the presence of other
elements. Its melting-point is 1,535 oC (2,795 oF), and it is believed to be the main component of the earth's core. Iron
ores are found in many kinds of rock throughout the world, the chief among them being haematite, magnetite (loadstone), and
siderite (ironstone). The yellow iron pyrites (FeS2) is known as fool's gold. Iron is obtained by heating iron oxide, the
ore's main constituent, with carbon (from coke). The carbon reacts with oxygen to form carbon dioxide, releasing the iron.
In the blast-furnace carbon is provided in the form of coke. The resulting pig-iron is brittle and contains 3--4 per cent
carbon and other impurities. Cast iron is made from pig-iron by re-melting and cooling. It is especially useful in casting.
Wrought iron is produced from pig-iron by puddling. It has less than 0.2 per cent carbon, is malleable and ductile, and was
used for making chains, anchors, bolts, and ornamental frameworks until it was superseded by mild steel. The element reacts
with acids and non-metals, and forms rust in moist air. It forms two sets of compounds: iron(II) compounds (ferrous compounds),
which contain the Fe2+ ion, and iron(III) compounds (ferric compounds), which contain the Fe3+ ion. Iron(II) compounds are
often pale green, and iron(III) compounds yellow-brown; the colours of many rocks are caused by the presence of iron. Iron
oxide (Fe2O3) is a red powder used as a paint pigment. Iron sulphate (FeSO4-7H2O) is employed as a weed-killer and wood preservative
and in the manufacture of inks, dyes, and pigments. (See also iron and steel industry.)
Iron is an essential element in diet and in the human body. It is present in enzymes, which control oxidation reactions,
and in haemoglobin, which transports oxygen in the blood. Haemoglobin also binds other inorganic molecules, including carbon
monoxide, which prevents uptake of oxygen. Pharmaceuticals containing iron are important for treating anaemia.
An iron is also an appliance for removing creases from textiles using heat and pressure. Simple flat-irons were in common
use by the 17th century and consisted of an elongated triangular plate of cast iron fitted with a handle. These were heated
on a fire or stove; later, they were internally heated by charcoal and then by coal, gas or paraffin. Modern irons are heated
electrically and are maintained at the appropriate temperature by a thermostat. Some types also produce steam from an internal
water reservoir to facilitate the removal of creases. Other types of iron are cordless and rechargeable. Some industrial irons
have a rotary motion.
vanadium (symbol V, at. no. 23, r.a.m. 50.94), a brilliant white transition metal that occurs naturally in patronite,
V2S5, vanadinite, Pb5(VO4)Cl, and crude oil. It is used mainly as a constituent of steels, to give strength at high temperatures
and corrosion-resistance. It is also added to copper alloys to increase strength and corrosion-resistance, especially in marine
environments. Vanadium-aluminium alloys are used in airframe construction, and vanadium oxide, VO, is a good industrial catalyst.
zinc (symbol Zn, at. no. 30, r.a.m. 65.38), a soft, white transition metal that quickly tarnishes to a blue-grey appearance.
The main ore is the sulphide (ZnS), known as zinc blende. It is roasted to form the oxide and then reduced by smelting with
carbon, after which it is purified by distillation. Other ores are smithsonite, ZnCO3, and hemimorphite, ZnSiO4-H2O. Zinc
is used widely in the manufacture of dry batteries and in the production of alloys such as brass and solder. It is alloyed
with aluminium to give the aluminium properties suitable for die casting. Zinc is also used for galvanizing or sherardizing
iron. Zinc oxide is used as a white paint pigment that does not blacken in hydrogen sulphide, as a filler for automobile
tyres and other rubber goods, and in medicinal ointments for skin irritations. Zinc chloride can serve as a flux for soldering
and as a wood preservative. Zinc sulphate is used in the production of the white paint pigment lithopone. Zinc is an essential
trace element in the growth of human beings and animals.
cadmium (symbol Cd, at. no. 48, r.a.m. 112.41), an unreactive silvery transition metal occurring in the rare mineral greenockite,
but extracted as a by-product of zinc production. It is used in alloys of low melting-point, in metals for bearings, in nuclear
reactor control rods, nickel-cadmium batteries, and in electroplating to protect and embellish more relative metals. Cadmium
sulphide is a yellow paint pigment. Many cadmium compounds are toxic.
hafnium (symbol Hf, at. no. 72, r.a.m. 178.49), one of the transition metals; it closely resembles zirconium and is usually
found in zirconium minerals. It is rather unreactive, and shows valency 4 in most of its compounds. A strong neutron absorber,
it is used for control rods in nuclear reactors.
rhenium (symbol Re, at. no. 75, r.a.m. 186.2), a rare transition metal extracted from flue dusts. It is silvery grey and
was first detected from its X-ray spectrum in 1925. It has a very high melting-point (3,180 oC, or 5,755 oF) and is chemically
similar to manganese. The element is hard and resistant to wear and corrosion. Its uses include alloy steels, fountain-pen
nib points, high-temperature thermocouples, electrical components, and as a catalyst.
tantalum (symbol Ta, at. no. 73, r.a.m. 180.95), a heavy grey transition metal. It occurs with niobium in the mineral
tantalite, which has the formula (Fe, Mn)(Nb, Ta)2O6. Tantalum alloys are used for dental and surgical instruments and for
spinnerets for synthetic fibre production. It is added to steels to prevent weld-decay and improves the performance of nickel
alloys in gas-turbines. Sintered tantalum is used for electrolytic capacitors. Tantalum forms an extremely hard carbide, which
is used as an abrasive and in cutting tools for machining steel.
titanium (symbol Ti, at. no. 22, r.a.m. 47.90), a commonly occurring transition metal that occurs naturally in rutile,
TiO2, and in ilmenite, FeTiO3, as well as in much organic matter. It is present in meteorites and in the Sun, and the rock
obtained by the Apollo 11 lunar mission contained up to 12 per cent of the metal. It has a high melting-point and is resistant
to corrosion. Titanium alloys are used extensively in aerospace technology and other applications requiring lightness and
high strength. Titanium is also used for hip replacements as it is not attacked by body fluids. Titanium dioxide is a white
solid used as a pigment in paint, and as a filler in paper, soap, and rubber. Titanium nitride is used to form a hard coating
on steel cutting tools.
platinum (symbol Pt, at. no. 78, r.a.m. 195.09), a silvery-white, very malleable and ductile transition metal long known
in South America. Although sparse and therefore precious, it occurs naturally in the form of fine black grains in alluvial
deposits of heavy sands and in heavy metal sulphide ores from which it can be readily obtained by reduction. Unaffected by
simple acids and fusible only at very high temperatures, it is used in jewellery, electrical contacts, and in laboratory equipment
that comes into contact with corrosive liquids and gases. As a finely divided black powder called 'platinum black' it is employed
as a catalyst in hydrogenation reactions. Platinum hexafluoride, PtF6, is a powerful oxidizing agent.
silver (symbol Ag, at. no. 47, r.a.m. 107.87), a brilliant white, malleable, transition metal. It has the highest known
electrical conductivity; and is one of the so-called precious metals. It occurs widely in nature--mostly in South Africa and
Russia--both in sulphide ores and as the native or free metal. Silver can be extracted from ores before smelting, by treating
with cyanide and then displacing with zinc, or by amalgamating with mercury followed by distillation. It normally shows a
valency of 1, although silver oxide, AgO, does exist; this is a black solid with a complex structure containing monovalent
and trivalent silver ions. A dark silver sulphide forms when silver tarnishes in air because of the presence of sulphur compounds.
The metal is used for ornaments and jewellery (silverware). Copper and brass objects are coated with silver by electroplating.
Large amounts of silver halide are used in photographic film.
cobalt (symbol Co, at. no. 27, r.a.m. 58.93), a hard, grey metallic element; it is one of the transition metals. Cobalt
oxide is obtained mainly as a by-product in the extraction of nickel, copper, and iron ores. It is reduced to the metal with
aluminium or hydrogen and then purified by electrolysis. Chemically resembling iron and nickel, cobalt forms ionic compounds
in which it shows valencies 2 and 3. It is commonly alloyed with other metals: with iron and nickel to make permanent magnets,
and in steels to improve their cutting and wear resistance. The metal is also an industrial catalyst. Cobalt oxide is used
in ceramics and glasses to give a blue colour and to neutralize the yellow from iron compounds. The radioactive isotope cobalt-60
is used as a tracer and in cancer therapy.
helium (symbol He, at. no. 2, r.a.m. 4.0), a colourless, odourless gas; it is one of the noble gases, and forms no true
chemical compounds. Although it occurs to a small extent on Earth, it was first discovered in the Sun from the analysis of
the solar spectrum. The element makes up about one-third of the mass of the universe. Although it is thought that most helium
in the universe was created in the first few minutes of the life of the universe after the Big Bang, it is also the end-product
of the carbon-nitrogen cycle and the proton-proton reaction within main sequence stars whereby hydrogen is converted into
helium with the production of energy which the stars radiate. Helium liquefies at -268 oC (-514 oF), and remains a liquid
down to absolute zero; it can only be solidified under pressure. At -271 oC (-520 oF) it becomes a superfluid; its viscosity
disappears, and its thermal conductivity becomes very high. Helium is found in ores of uranium and thorium but the main source
of the element is natural gas, from which it is obtained by liquefaction of all the other components; it is used to provide
an inert atmosphere in welding and as a safe alternative to hydrogen in balloons. Mixed with oxygen, it forms a breathing
mixture which reduces the danger of 'the bends' in deep-sea diving. Liquid helium is an important coolant for superconducting
systems and other low-temperature applications.
argon (symbol Ar, at. no. 18, r.a.m. 39.9), a gaseous element found in minute proportions (c. 1 per cent) in the Earth's
atmosphere. A colourless gas, argon is one of the noble gases and forms no chemical compounds. It is obtained from the fractional
distillation of air. It is used in gas-discharge lamps, to provide an inert atmosphere in electric light bulbs, and create
a non-oxidizing atmosphere in modern arc-welding equipment. Most argon has arisen from the decay of radioactive potassium-40.
radon (symbol Rn, at. no. 86, r.a.m. 222), the heaviest noble gas. It occurs naturally and has been noticed to increase
in groundwater before seismic activity. It is highly radioactive and produced by the radioactive decay of heavy elements such
as radium. The most stable isotope, radon-222, has a half-life of 3.825 days and is used in tracer studies.
krypton (symbol Kr, at. no. 36, r.a.m. 83.80), a colourless unreactive gas which is used together with other noble gases
in discharge lamps. It forms a few unstable compounds such as krypton difluoride, KrF2.
xenon (symbol Xe, at. no. 54, r.a.m. 131.30), one of the noble gases, discovered in 1898 as a result of the fractional
distillation of liquid air. It constitutes one part in twenty million of the atmosphere. Formerly xenon was thought to be
totally inert, but various xenon compounds have now been prepared, particularly with fluorine, for example XeF2 and XeF4.
The ionic compound Xe+PtF6- was the first noble-gas compound to be discovered. Commercially xenon is obtained from liquid
air; it is used in special lamps and discharge tubes and in the control of nuclear fission chain reactions.
yttrium (symbol Y, at. no. 39, r.a.m. 88.91), a metallic element, belonging to the lanthanides. It is used in making europium
phosphors, which give the red colour in television tubes. Analysis of lunar rock from the Apollo 11 mission indicated an unusually
high yttrium content.
plutonium (symbol Pu, at. no. 94, r.a.m. 244), one of the transuranic elements and a member of the actinides. It was
synthesized in 1940 and used in the atomic bomb dropped on Nagasaki in 1945. There are traces of the element in uranium
ores, but it is produced on a larger scale from uranium-238 in nuclear reactors; in this process a U-238 atom absorbs a
neutron to form Pu-239. There are now six known allotropes, each with a differing density, coefficient of expansion, and resistivity.
All the isotopes are radioactive, plutonium-239 having a half-life of 24,360 years. Above a certain critical size, plutonium-239
can initiate a nuclear explosion; 1 kilogram has an energy potential of about 1014 joules. It is used as a nuclear fuel in
the form of alloys. Plutonium-238, obtained from neptunium, is employed as a nuclear power source in space exploration.
uranium (symbol U, at. no. 92, r.a.m. 238.03), a dense, white, metallic element, a member of the actinides; it is radioactive,
decaying over a long period to lead. Measurement of the lead content of uranium-containing rocks can be used to date the rock.
The importance of uranium stems from its use in producing nuclear energy, both in reactors and in bombs. Naturally occurring
uranium consists of three isotopes, of mass numbers 234, 235, and 238. Uranium-235 has an abundance of only 0.71 per cent,
but it is the only naturally occurring isotope that is fissile--that is, can be split by a slow neutron to form smaller nuclei
and release energy. The fission process also produces more neutrons which can initiate fission in other nuclei, so starting
a chain reaction. The much more abundant (99.28 per cent) uranium-238 is used in breeder reactors to produce plutonium. Although
uranium is probably about forty times as abundant in nature as silver is, it is not found uncombined. Indeed it occurs only
sparingly in ores, the most notable of which are uraninite, pitchblende, carnotite, and coffinite, a silicate. These are mined
mainly in Canada, the USA, Russia, Zaire, South Africa, France, Niger, Namibia, and Australia. Such is its value that ores
with as little as one part of uranium in a thousand have been processed for its extraction. (See also nuclear fuel.)
calcium (symbol Ca, at. no. 20, r.a.m. 40.08), a silvery white metal, the fifth most abundant element in the Earth's crust.
It occurs in many minerals: as calcium carbonate in, for example, limestone, chalk, and marble, as calcium fluoride in fluorite,
and as calcium sulphate in gypsum. It also occurs in seawater, and as calcium phosphate in bones and teeth. The hardness of
water is due chiefly to calcium compounds. Calcium is one of the alkaline earth metals. It is a reactive metal; on treatment
with non-metals, water, and acids it gives ionic compounds in which the metal has a valency of 2. The metal is obtained by
the electrolysis of molten calcium chloride (produced in the manufacture of sodium carbonate), followed by distillation under
high vacuum or in argon to obtain the pure metal. Calcium is used as a dehydrating agent for organic solvents and to remove
gases from molten metals prior to casting. It is also used as a hardening agent in lead for cable covering, for making storage
battery grids and bearings, and, alloyed with silicon, in steel.
germanium (symbol Ge, at. no. 32, r.a.m. 72.59), a brittle whitish metalloid element in Group 14 (formerly IVB) of the
periodic table. It is sometimes present in coal and can be found in chimney soot. Industrially it is extracted from the flue
dust of zinc smelters. Compounds, except for the oxide, GeO2, are rare. Germanium purified by zone refining is used to make
transistors, rectifiers, and other semiconductor devices. Germanium dioxide is used in the manufacture of specialized optical
glasses.
indium (symbol In, at. no. 49, r.a.m. 114.82), a soft, silver, metallic element in Group 13 (formerly IIIB) of the periodic
table. It reacts readily with acids, the halogens, and sulphur with a principal valency of 3. It is used in the manufacture
of semiconductor devices, and to monitor neutron fluxes near nuclear reactors.
thallium (symbol Tl, at. no. 81, r.a.m. 204.37), a soft, white, lead-like metal in Group 13 (formerly IIIB) of the periodic
table, named after the intense green spectral line (Greek thallos, green shoot) that identifies the element. It occurs naturally
in crookesite and lorandite, often found with sulphur and selenium ores. Its compounds are used to make optical glass of high
refractive index. The metal and its salts are poisonous and are used as pesticides.
fluorine (symbol F, at. no. 9, r.a.m. 19.00), a yellow-green gas and one of the halogens. The most reactive non-metal,
it is an extremely powerful oxidizing agent, which forms compounds with all the elements except helium, argon, and neon and
reacts explosively with many substances. It occurs widely in the minerals fluorite (fluorspar) and cryolite, but can only
be obtained pure by the electrolysis of a molten mixture of hydrogen fluoride, HF, and potassium fluoride, KF. Its extreme
reactivity requires the use of fluorine-resistant materials in constructing manufacturing plant. The pure form is used in
some rocket fuels. Fluorine is also used in the refining of aluminium and in separating isotopes of uranium (see nuclear fuels).
Since the 1920s, there has been a growth in the production of organic fluorine compounds. The use of some of these materials
(chlorofluorocarbons) as refrigerants, propellants, and in expanded foam plastics has declined with concern about pollution,
but fluorocarbons and fluorinated polymers still have a wide range of specialist applications. Fluorine is also used for the
fluoridation of drinking water.
chlorine (symbol Cl, at. no. 17, r.a.m. 35.45), a yellow-green choking gas; it is a reactive non-metallic element in Group
17 (formerly VII B), the halogens, and in the free state consists of Cl2 molecules. With metals it forms ionic compounds which
contain the Cl- ion, and with non-metals covalent compounds; it also forms compounds with oxygen in which it shows valencies
3, 5, and 7. It occurs as sodium chloride in seawater, from which it is obtained by electrolysis in a Castner-Kellner cell,
and in rock salt. Widely used for disinfecting water supplies and swimming pools, large amounts are also used in bleaches
for woodpulp in paper and textile manufacture. In reactions with hydrocarbons, chlorine is used to manufacture PVC, hydrochloric
acid, and a wide variety of other chemicals. Chlorine gas was used as a poison gas in World War
bromine (symbol Br, at. no. 35, r.a.m. 79.90), a dense, deep reddish-brown liquid element belonging to the halogens. It
readily vaporizes to form a reddish brown vapour. It occurs as bromide in sea-water, from which it is extracted commercially,
and in salt deposits. Its main application has been as 1,2-dibromoethane (C2H4Br2), an additive to leaded petrol, but since
the introduction of lead-free petrol this application has declined. It is also used in the manufacture of silver bromide for
photographic emulsions, in fire-extinguishing and flame-retardant agents, in fumigants, and in chemical synthesis. Chemically,
it reacts with most metals and non-metals.
iodine (symbol I, at. no. 53, r.a.m. 126.90), a black shiny solid in Group 17 (formerly VIIB) (the halogens) of the periodic
table. On gentle warming it sublimes to a violet vapour; both the solid and the vapour contain I2 molecules. It dissolves
in many organic solvents and in potassium iodide solution, but it is not very soluble in water. Less reactive than the other
halogens, it forms compounds with most metals and non-metals; and it also forms compounds in which it has the valencies 1,
3, 5, and 7. Sodium iodide is a minor constituent of sea water and is concentrated in seaweed, which has been used as a source
of iodine. The main source is a mineral found in Chile called caliche. It is used in quartz-halogen lamps, to make photographic
materials, and as an antiseptic (tincture of iodine). Iodine is an essential element in the body, occurring mainly in the
thyroid gland: a radioactive isotope of iodine, iodine-131, is used in medicine to check for abnormal activity of the thyroid
(see nuclear medicine).
astatine (symbol At, at. no. 85, r.a.m. 210), the heaviest member of the halogens. All its isotopes are strongly radioactive;
the most stable is astatine-210 with a half-life of eight hours. The element is made by bombarding bismuth with alpha particles;
its chemistry is similar to that of iodine.
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