Atomic structure of sodium (Na). The nucleus of every atom contains two types of particle: protons and neutrons. Spinning round...Read More >>Atomic structure of sodium (Na). The nucleus of every atom contains two types of particle: protons and neutrons. Spinning round the nucleus are a third type of subatomic particle: electrons. There are always the same number of electrons and protons in a neutral atom. The electrons travel in different shells (layers). When atoms bond together, it is the electrons in the outer shells that are involved.An element is a substance made up of atoms of the same type. It cannot be broken down into simpler substances. Different elements have different characteristics, which are determined by the number of subatomic particles (protons, neutrons and electrons) they have. Scientists have found approximately 100 natural elements so far; a further 15 or so artificial kinds have been made by scientists in laboratories. These elements are divided into metals, semi-metals and non-metals. An atom is the smallest part of an element that can exist. All the elements have been arranged in a table, called the Periodic Table, in order of their atomic numbers—the number of protons an element has in each of its atoms. Elements in the same group on the Table have similar properties.
Aluminium (chemical symbol Al; atomic number 13) is a poor metal, also called a “post-transition metal”. Like the other poor metals, it is soft. Aluminium has low density (is “light”) and is a good thermal and electrical conductor. As a result, aluminium is widely used in vehicle and plane construction, drinks cans and power lines. Since aluminium bonds very easily with oxygen, it is rarely found as a pure element. Most aluminium is obtained from bauxite ore.
Antimony (chemical symbol Sb; atomic number 51) is a semi-metal, also called a metalloid. Semi-metals have properties in between metals and non-metals. Like other semi-metals, antimony is metallic in appearance (it is grey and shiny) but too brittle to use on its own for construction or tools. Antimony is often used in alloys with other metals to harden them. It is alloyed with lead in bullets, and with tin in pewter. It is also used in flame-retardants, electronics and some pharmaceuticals. Antimony is toxic (poisonous).
Argon (chemical symbol Ar; atomic number 18) is a noble gas. It is odourless and colourless when at room temperature and pressure. All the noble gases, including helium, neon and xenon, have the maximum number of electrons possible in the outer shell of their atoms. This makes them stable and non-reactive. They rarely bond with other elements.
Argon is used for a number of purposes where its non-reactive (“inert”) nature is useful: in fluorescent lighting tubes, where it prevents oxygen eroding the hot filament, and in graphite electric furnaces where it prevents the graphite from burning. Argon is the third most abundant gas in the Earth’s atmosphere.
Arsenic (chemical symbol As; atomic number 33) is a semi-metal, also called a metalloid. Semi-metals have properties in between metals and non-metals. Like other semi-metals, arsenic is metallic in appearance (it is grey and shiny) but too brittle to use on its own for construction or tools. Arsenic is commonly used in alloys with other metals such as lead or copper. Arsenic is toxic (poisonous). In the past, its toxicity led to its use in pesticides, but environmental and health concerns make this use rare today.
X-rays do not pass through barium. In a “barium meal” examination, a patient swallows barium sulphate mixed with water, which...Read More >>X-rays do not pass through barium. In a “barium meal” examination, a patient swallows barium sulphate mixed with water, which coats the lining of the stomach and duodenum. This allows an X-ray to take a clear image.
Barium (chemical symbol Ba; atomic number 56) is one of the alkaline earth metals. Like the other alkaline earth metals, barium is a shiny, silvery metal at room temperature and pressure. Barium is chemically reactive (it bonds easily with other elements) so it is never found in nature as a pure element. It is usually extracted from minerals such as barite and witherite. Barium metal is used in metal alloys. Barium compounds have a wider range of uses: for example, barium sulphate is used for getting X-ray images of the digestive system (a “barium meal”) and barium nitrate is used in fireworks to give a green colour.
An alloy of beryllium and copper is sometimes used for tools because it does not create sparks, is not magnetic, is extremely...Read More >>An alloy of beryllium and copper is sometimes used for tools because it does not create sparks, is not magnetic, is extremely strong and is slow to corrode. Beryllium copper tools are useful in coal mines or oil rigs, where there may be explosive gases.
Beryllium (chemical symbol Be; atomic number 4) is one of the alkaline earth metals. Like the other alkaline earth metals, beryllium is a shiny, silvery metal at room temperature and pressure. Beryllium does not occur naturally as a pure element, but is found combined with other elements in more than 100 rare minerals. One of these minerals, beryl, comes in the form of the gemstones aquamarine and emerald. Beryllium is often used in alloys with other metals such as aluminium and copper because of its strength, low density (“lightness”) and stability over a wide range of temperatures.
Borosilicate glass is created by adding boric oxide to traditional glass. This makes it less likely to crack when exposed to high...Read More >>Borosilicate glass is created by adding boric oxide to traditional glass. This makes it less likely to crack when exposed to high temperatures. Borosilicate glass is commonly used for cookware and laboratory equipment.
Boron (chemical symbol B; atomic number 5) is a semi-metal, also called a metalloid. Semi-metals have properties in between metals and non-metals. Like other semi-metals, boron is metallic in appearance (it is grey and shiny) but too brittle to use on its own for construction or tools. Boron metal is found in meteoroids—small lumps of rock in space, once parts of comets or asteroids—but does not occur naturally on Earth. Boron is extracted from rocks containing boron compound minerals, such as borax (sodium borate) and kernite (sodium borate hydroxide). Boron compounds are used in fibreglass, polymers, ceramics, pharmaceuticals, fertilizers and insecticides.
Bromine (chemical symbol Br; atomic number 35) is a halogen. The halogens are non-metallic elements that are highly reactive (they bond easily with other elements) because they are missing an electron in their atoms' outer shells (they have seven). When bonded with most metals, the halogens form salts—halogen means “salt former”. The elements in the halogen group may be gas, solid or liquid at room temperature. With a melting point of -7.2°C (19°F), bromine is one of only two elements (mercury is the other) that are liquid at room temperature. Liquid bromine is red-brown and evaporates easily, creating an orange vapour with an unpleasant smell.
Bromine is toxic (poisonous) and corrosive (burns). Bromine does not occur naturally in elemental form, but can be found as bromide salts (compounds containing bromine) in rocks and seawater. Bromine compounds are used in flame retardants, plastics and pharmaceuticals.
Cadmium (chemical symbol Cd; atomic number 48) is a dense, shiny metal that is a good electrical conductor. Cadmium is bluish-silver. It is easily shaped and is resistant to corrosion (decay caused by reactions to oxygen or water), which makes it useful as a protective layer for other metals. However, cadmium is toxic (poisonous) so its usage has fallen, although the compound cadmium telluride is today often used for photovoltaic panels. Cadmium is usually obtained from rocks containing the mineral greenockite (cadmium sulphide), which is rare.
Caesium (chemical symbol Cs; atomic number 55) is one of the alkali metals. Alkali metals react with water to form alkaline solutions. They are generally soft, shiny and a pale silvery colour. Caesium has a very low melting point (28.5°C / 83.3°F) for a metal, making it one of only five metals to be liquid near room temperature—the others are mercury, francium, gallium and rubidium. It is the softest of all elements. Caesium is hazardous, as it ignites in air and explodes on contact with water.
Caesium may be stable (non-radioactive) or unstable (radioactive)—a radioactive isotope (form) of caesium is caesium-137, which is formed by nuclear fission. The compound caesium formate is commonly used as a “drilling fluid” to help in oil extraction, lubricating drills and maintaining pressure during drilling. The isotope caesium-133 is used in atomic clocks. Caesium is usually obtained by mining the rare mineral pollucite.
Calcium carbonate is one of the most common calcium compounds. These calcium carbonate deposits are found at the hot springs of...Read More >>Calcium carbonate is one of the most common calcium compounds. These calcium carbonate deposits are found at the hot springs of Pamukkale in Turkey. The spring water is saturated with calcium carbonate, which is deposited as the water meets the air. The deposits eventually harden into the sedimentary rock called travertine.
Calcium (chemical symbol Ca; atomic number 20) is one of the alkaline earth metals. Like the others, calcium is a shiny, silvery metal at room temperature and pressure. Calcium is so soft it can be cut with a knife. Vital to living organisms, including humans, it helps build strong bones, teeth and shells. While calcium is the fifth most abundant element in the Earth’s crust, it is found in minerals such as calcite (calcium carbonate) rather than as a pure element. Calcium metal is used in metal alloys and cement. Calcium compounds have a variety of uses: calcium sulphate is blackboard chalk; calcium hypochlorite is used in disinfectants and deodorants; calcium gluconate is a food additive.
Charcoal briquettes made from sawdust. Charcoal is a form of carbon, made by heating wood or other organic matter in the absence...Read More >>Charcoal briquettes made from sawdust. Charcoal is a form of carbon, made by heating wood or other organic matter in the absence of air ("charred").
Carbon (chemical symbol C; atomic number 6) is a non-metal that is solid at room temperature. Unlike most elements, carbon occurs as several allotropes (allotropes are different forms of an element, caused by the atoms bonding together differently). Well-known carbon allotropes are: diamond, which is transparent and extremely hard; graphite, which is black and soft; and amorphous carbon—coal is mostly amorphous carbon. Carbon is the fourth most common element in the Universe and makes up one-fifth of the human body.
Atoms of carbon bond easily with other atoms, forming more than 10 million known compounds, more than any other element. Common carbon compounds include carbon dioxide in the air, hydrocarbons (such as fossil fuels, petrochemicals and plastics), carbonate rocks (such as limestone and marble), carbohydrates (such as sugars and starches) and DNA.
Chlorine (chemical symbol Cl; atomic number 17) is a halogen, a group of non-metallic elements. At room temperature and pressure, chlorine is a yellow-green gas. The halogens are highly reactive because they are missing an electron in their outer shells (they have seven). They bond easily with most metals to form salts. The most common compound of chlorine is sodium chloride: table salt. Pure chlorine is rare on Earth: it is usually extracted from saltwater.
Chlorine is a common oxidizing agent, meaning it readily accepts electrons from other atoms or molecules. Oxidation can kill microbes or whiten a substance, so for this reason, chlorine is commonly used as a bleach and disinfectant. It is also used in the chemical industry to cause reactions and form useful compounds, such as polyvinyl chloride (PVC).
A Chinese Ming dynasty (1368–1644) dish painted with cobalt blue pigment.Cobalt (chemical symbol Co; atomic number 27) is a transition metal. These metals are usually dense, shiny and make good electrical conductors. Along with iron and nickel, cobalt is one of three naturally occurring metals that are magnetic at room temperature. Cobalt is not found naturally in elemental form but can be produced from smelting various minerals. Cobalt metal is used to produce very hard alloys, used for products such as jet engines, drill bits and prosthetic joints.
For thousands of years, the naturally-occurring compounds cobalt aluminate and cobalt silicate have been used for their blue colour—called cobalt blue—for colouring ceramics, glass and paints.
The Statue of Liberty is coated with copper, which has given it a greenish colour, after many years of exposure to oxygen in the...Read More >>The Statue of Liberty is coated with copper, which has given it a greenish colour, after many years of exposure to oxygen in the air.
Copper (chemical symbol Cu; atomic number 29) is a transition metal. It is orangey in colour, soft and easily shaped. It is also a very good conductor of heat and electricity. Copper slowly turns greenish when exposed to oxygen in the air, but this layer of copper oxide protects the copper below from damage—unlike the rust formed on iron.
Copper is widely used as a pure metal, most commonly in electrical wires and devices, construction and machinery. It is also often combined with other metals to form alloys, such as brass (with zinc), bronze (with tin) and cupronickel (with nickel, widely used for coins). Copper is mined from the Earth’s crust and can also be extracted from minerals such as chalcopyrite.
Fluoride tooth treatmentFluorine (chemical symbol F; atomic number 9) is a halogen. The halogens are non-metallic elements that are highly reactive (bonding easily with other elements) because they are missing an electron in their atoms' outer shells (they have seven). Fluorine forms compounds with nearly all the other elements. Fluorine does not occur naturally in elemental form, but can be extracted from minerals, such as fluorite. The elements in the halogen group may be gases, solids or liquids at room temperature: fluorine is a pale yellow gas.
Fluoride, a form of fluorine, is often added to drinking water and toothpaste to prevent tooth decay by strengthening tooth enamel. Compounds of fluorine are widely used in steel-making, aluminium-refining, the chemical industry and pharmaceuticals.
Gold (chemical symbol Au; atomic number 79) is a transition metal. It is yellow, shiny, soft and easily shaped. It is a good conductor of electricity and slow to corrode (be destroyed by chemical action). It is one of the least reactive elements and is found in its elemental state in rocks and sediments. It also occurs naturally as an alloy with silver, copper and palladium. For millennia, gold’s useful and attractive properties (as well as its rarity) have led to its being highly valued as a material for jewellery, art and coins. Today, it is no longer used for coinage, although gold bullion (bars and ingots) is often kept as an investment. A common industrial use of gold is as an electrical connector.
Helium (chemical symbol He; atomic number 2) is a noble gas. The noble gases are sometimes called “inert” or “unreactive” gases because they do not easily form compounds with other elements. Helium has the lowest boiling point (-268.9°C / -452°F) of all the elements, so it is a gas except for in exceptionally cold conditions—or extremely hot conditions, when it becomes plasma. Helium gas is colourless, tasteless and odourless. Helium is the second most abundant element in the Universe, after hydrogen, although it is rare in the Earth's atmosphere.
Most helium for commercial use is extracted from natural gas. The best-known use of helium is in balloons and airships, but it is chiefly used in cryogenics (creating very low temperatures) and in various industrial processes.
Hydrogen (chemical symbol H; atomic number 1) is the simplest and lightest element: its atom has just two subatomic particles: one proton and one electron. At room temperature and pressure, hydrogen is a colourless, odourless, tasteless, non-toxic (not poisonous), highly combustible (quick to catch fire) gas. The most abundant element in the Universe, hydrogen forms the bulk of the Sun and most other stars.
Hydrogen easily forms covalent bonds—chemical bonds in which pairs of electrons are shared between atoms—with most non-metallic elements. As a result, the majority of hydrogen found on Earth is in compounds, most commonly in water (joined to oxygen to form H2O), as well as hydrocarbons (joined to carbon to form fuels) and carbohydrates (joined to carbon and oxygen to form sugars and starches).
In 1781, it was discovered that hydrogen produces water when burned, for which it was given the name hydrogen (from the Greek hydro, meaning “water”, and genes, meaning creator).
Iodine (chemical symbol I; atomic number 53) is a halogen. The halogens are non-metallic elements that are highly reactive (they bond easily with other elements) because they are missing an electron in their atoms' outer shell (they have seven). Iodine is a blue-black solid that becomes a purple gas at room temperature (iodine comes from the Greek iodes, meaning “violet”). Iodine is rare on Earth, but iodine compounds, in the form of salts, are found in seawater. We need iodine for the correct working of the thyroid gland, so iodine compounds are often given as dietary supplements. Iodine is also used in the chemicals industry.
Iron (chemical symbol Fe; atomic number 26) is a transition metal. These metals are usually dense, shiny and make good electrical conductors. Along with nickel and cobalt, iron is one of three naturally occurring metals that are magnetic at room temperature. Iron is the fourth most common element in the Earth’s crust, but it reacts easily with oxygen, so it is most often found as iron oxide minerals. Iron is obtained from these ores by heating them until they melt, a process called smelting.
Essential to construction, machinery and chemical industries, iron is the most widely used metal of all. Because of its tendency to rust (it oxidizes in air), it is often painted or coated. Iron is usually mixed with other metals in alloys to make it stronger or more resistant to rusting or both. Alloys include cast iron (with carbon) and steel (with carbon and elements such as manganese, phosphorus, sulphur and silicon).
Iron is also an important element in the bodies of all living things. If humans lack iron in their diet, they may suffer from the iron-deficiency condition, anaemia.
Lead (chemical symbol Pb; atomic number 82) is a poor metal, also called a “post-transition metal”. Like the other poor metals, lead is soft. It is shiny silver-blue but quickly reacts with oxygen in air to become dull grey. Elemental lead is rare on Earth: lead is most often obtained from lead compound minerals, such as galena (lead sulphide).
Lead is the heaviest non-radioactive element. Its density makes it useful as a shield from X-rays and gamma rays—for example, in lead aprons worn to protect other parts of the body during X-rays. Lead is also used in bullets, car batteries, ballast and weights, construction and electronics. Lead is poisonous to humans and animals, and so is no longer used in pipes and paints.
Lithium is the least dense solid element: it floats in oils and is one of three metals that can float on water (the others are...Read More >>Lithium is the least dense solid element: it floats in oils and is one of three metals that can float on water (the others are sodium and potassium).
Lithium (chemical symbol Li; atomic number 3) is an alkali metal. These metals react with water to form alkaline solutions. At room temperature and pressure, alkali metals are generally soft, shiny and pale grey. Lithium is the lightest metal and the least dense solid element of all. It is a good conductor of heat and electricity. Like all alkali metals, lithium is flammable and highly reactive. It bonds so easily with other elements that lithium metal is never found in nature, but is obtained from compound minerals and salts in seawater, rocks and clay.
Lithium and its compounds are used in lithium batteries (as anodes, through which electrical charge flows), in light but strong metal alloys, such as with aluminium, in heat-resistant glass and ceramics and in mood stabilizing medications (lithium salts affect the nervous system).
Magnesium is used for emergency fire starter kits. A block of magnesium is being filed with a pocket knife to create sparks,...Read More >>Magnesium is used for emergency fire starter kits. A block of magnesium is being filed with a pocket knife to create sparks, which are igniting a small pile of magnesium shavings.
Magnesium (chemical symbol Mg; atomic number 12) is an alkaline earth metal. Like the other alkaline earth metals, magnesium is a shiny, silvery metal at room temperature and pressure. However, it tarnishes quickly on being exposed to air. Magnesium is chemically very reactive (it bonds easily with other elements) so it is never found in nature in elemental form, but it can be obtained by from magnesium salts dissolved in seawater. It burns with a brilliant white light, making it useful for emergency flares and firework sparklers.
Magnesium's low density makes it good for lightweight alloys, particularly with aluminium, for construction, vehicles and electronics. Magnesium is also used in pharmaceuticals—for example, in products that combat stomach acid or constipation.
Mercury (chemical symbol Hg; atomic number 80) is a transition metal. Mercury is rare in the Earth’s crust but can be extracted from ores such as cinnabar (mercury sulphide). Mercury has the lowest melting point of any metal (-38.8°C / -37.9°F), making it liquid at room temperature. It is used in some thermometers although concerns about its toxicity have reduced this use. Mercury can dissolve many other metals—apart from iron, platinum and a few others—to form amalgams; silver, tin and copper amalgams are used for dental fillings.
Mercury vapour is used in fluorescent lights. A tube coated with phosphor is filled with mercury vapour. When electricity passes through the vapour, it produces ultraviolet light, which makes the phosphor fluoresce.
Neon (chemical symbol Ne; atomic number 10) is a noble gas, also called an “inert” or “inactive” gas. Like the other noble gases, it is an odourless, colourless gas when at room temperature and pressure. The noble gases all have the maximum number of electrons possible in the outer shell of their atoms. This makes them stable and non-reactive—they rarely bond with other elements. Neon is the fifth most common element in the Universe (after hydrogen, helium, oxygen and carbon) but makes up only a tiny portion of Earth’s atmosphere. Neon can only be obtained from the distillation of liquid air, making it expensive.
Neon's most well-known use is in neon signs. Electricity is passed through a sealed glass tube filled with neon gas. The neon atoms become excited and give off photons (elementary particles) of red light. A mixture of different noble gases can make different colours.
Nickel (chemical symbol Ni; atomic number 28) is a transition metal. These metals are usually dense, shiny and make good electrical conductors. Along with iron and cobalt, nickel is one of three naturally-occurring metals that are magnetic at room temperature. Nickel is hard, easily shaped and silvery-gold coloured.
Nickel is slow to react with oxygen so it is often used for corrosion-resistant coatings and alloys, such as stainless steel. The alloy cupronickel is often used in coins. It is also used in the chemical industry as a catalyst (a substance that speeds up a reaction) in hydrogenation. Nickel is obtained from ores such as pentlandite, an iron-nickel sulphide.
Nitrogen (chemical symbol N; atomic number 7) is a non-metal that is a gas at room temperature. Colourless, odourless and tasteless, nitrogen makes up more than three-quarters of the Earth’s atmosphere. Nitrogen is produced industrially by the distillation of liquid air. At room temperature, nitrogen combines with very few other elements, but nitrogen compounds are essential to living organisms (in proteins and nucleic acids).
Nitrogen is widely used in the chemical industry: for example, ammonia, a compound of nitrogen and hydrogen, is used in fertilizers, cleaners and pharmaceuticals. At a very low temperature (-196°C / -321°F), nitrogen becomes a liquid and can be used to rapidly freeze materials.
Fighter pilot wearing an oxygen mask: oxygen is delivered from a tank to the pilot so he can fly at high altitude, where the...Read More >>Fighter pilot wearing an oxygen mask: oxygen is delivered from a tank to the pilot so he can fly at high altitude, where the atmosphere is thinner, i.e. there is less oxygen.
Oxygen (chemical symbol O; atomic number 8) is a non-metallic element that is a gas at room temperature. Colourless, odourless and tasteless, oxygen is one of the commonest elements on Earth. It makes up one-fifth of the atmosphere and is found in most minerals in the Earth’s crust. Bonded with hydrogen, it forms water. Oxygen bonds easily with many other elements to form compounds called oxides in a chemical reaction called oxidation. Sometimes this is a slow process, as when iron turns to rust (iron oxide) in damp air. But if oxygen reacts very quickly, combustion (burning) takes place, with flames, light and heat given off.
Oxygen is essential for all living things (except for a few specialized types of microbes): they must take in oxygen to stay alive. This is because oxygen is a vital part of chemical changes inside each microscopic living cell, which break apart food substances to obtain the energy for life.
Phosphorus (chemical symbol P; atomic number 15) is a non-metallic element. Solid at room temperature, it has several different allotropes (forms), including white, red, violet and black phosphorus. White phosphorus glows when exposed to oxygen. As a component of DNA and cell membranes, phosphorus is essential to all living things.
Phosphorus is highly reactive (it bonds easily with other elements) so it is found only as compounds in phosphate minerals. These are used to produce fertilizers, detergents and matches. When a safety match is struck against the surface of its box—which is coated with red phosphorus and ground glass—the friction produces enough heat to turn the very small amount of red phosphorus on the match head into white phosphorus, which catches fire on contact with air.
Platinum (chemical symbol Pt; atomic number 78) is a transition metal. It is shiny, grey, dense and easily shaped. It is very rare in the Earth’s crust and is considered a precious metal. Platinum is the least reactive metal, and so is useful for electronic parts, dentistry equipment and the catalyst in catalytic converters (which convert toxic pollutants in vehicle exhaust gas to less toxic ones). Platinum is very slow to corrode, which makes it popular for jewellery.
Plutonium (chemical symbol Pu; atomic number 94) is an actinide, a group of radioactive metals. The atoms of a radioactive element are unstable: they are likely to break up. Radioactivity, also called radioactive decay, is the process by which the nucleus of an unstable atom loses energy by emitting particles or rays. Radioactivity harms living things, but under controlled conditions it is very useful for generating energy. Tiny quantities of plutonium exist in nature, but nearly all plutonium is usually produced in nuclear reactors, in which the nuclear fission process converts uranium to plutonium.
There are 15 to 20 isotopes of plutonium (isotopes are forms of an element that have the same number of protons in the atom but a different number of neutrons). Two isotopes of plutonium, plutonium-239 and plutonium-249, are fissile—the energy from their atoms can be harnessed for nuclear chain reactions to take place—and so are used in nuclear reactors and weapons.
Potassium (chemical symbol K; atomic number 19) is an alkali metal. At room temperature and pressure, these metals are generally soft, shiny and a pale silvery colour. Potassium reacts violently with water, making enough heat to ignite the hydrogen emitted in the reaction, which burns with a lilac flame. Potassium also reacts strongly to oxygen in air, forming potassium peroxide, turning the metal dull grey. Potassium is so reactive that the metal is never found in nature; it is obtained instead from compound minerals and salts in seawater and rocks.
Potassium is a vital mineral needed for the human body's cells (and those of all living things) to function. It accumulates in the cells of plants, so fresh fruit and vegetables are a good source of it. Potassium used to be extracted from the ashes of plants, giving the name of its salts: "potash". Crops growing in field rapidly deplete the soil of potassium, hence the need for fertilizers containing potassium compounds. Potassium nitrate, one of the main ingredients of gunpowder, is used in rocket propellants and gunpowder as well as fertilizers.
Radium (chemical symbol Ra; atomic number 88) is one of the alkaline earth metals. Marie and Pierre Curie discovered radium in 1898. Radium is silvery-white but it quickly reacts with nitrogen in the air to form a black layer of radium nitride. Radium has 33 isotopes (isotopes are forms of the element that have the same number of protons in the atom but a different number of neutrons). All of them are radioactive, which means that their atoms are unstable and likely to break up. As they do so, the nuclei lose energy by emitting particles or rays. Radium is so radioactive that it kills living cells, and its use is confined to checking for flaws in metallic parts of machines or structures. Radium is present in tiny quantities in uranium ores.
Silicon (chemical symbol Si; atomic number 14) is a semi-metal, also called a metalloid. Semi-metals have properties in between metals and non-metals. Like other semi-metals, silicon is metallic in appearance (it is grey and shiny) but too brittle to use on its own for construction or tools. Silicon is not found in nature, but over 90% of the Earth’s crust is made up of silicate minerals (compounds that contain silicon). Silicate minerals are used widely in gravel, cement, glass and ceramics. Silicones—used for cookware, adhesives and contact lenses—are rubber-like polymers (large molecules) consisting of silicon, carbon, hydrogen and oxygen atoms. Silicon is central to the electronics industry, because of its use as a semiconducting material in integrated circuits.
Silver is often used in mirrors that generate solar power by reflecting sunlight onto a small area. This is a dish engine system,...Read More >>Silver is often used in mirrors that generate solar power by reflecting sunlight onto a small area. This is a dish engine system, which concentrates light on to a receiver. Fluid in the receiver is heated and used by an engine to generate electricity.
Silver (chemical symbol Ag; atomic number 47) is a transition metal. It is soft, grey-white and shiny. It is the most reflective element and also has the highest electrical and thermal conductivity of any metal. These properties make it extremely useful for a range of purposes, from jewellery and utensils to electrical conductors, mirrors and solar panels. Silver compounds are used in photographic film, medical instruments and disinfectants. Silver is found in the Earth’s crust in its pure form, alloyed with other metals and in minerals such as argentite.
Sodium (chemical symbol Na; atomic number 11) is an alkali metal. These metals react with water to form alkaline solutions. They are generally soft, shiny and a pale silvery colour. Sodium is never found in its metallic form in nature, but sodium compounds are very common in the Earth’s crust and in seawater. Some sodium compounds are extremely useful. Sodium chloride (common salt) is the salt most responsible for the “saltiness” of the oceans. It is used to de-ice streets and pavements, in the chemical industry and in food (some sodium is needed in the diet to regulate blood pressure). Sodium hydroxide, known as lye, is used to make soaps, paper and textiles. Sodium carbonate is used in glassmaking, water-softening and dyeing.
Strontium (chemical symbol Sr; atomic number 38) is one of the alkaline earth metals. Like the other alkaline earth metals, strontium is a shiny, silvery metal at room temperature and pressure. Strontium reacts strongly with both oxygen and water, so it is never found in nature in its elemental form, but can be extracted from minerals such as celestine and strontianite.
Strontium was used for producing glass for cathode ray tubes in televisions and computer monitors, because it prevents the emission of X-rays, but other types of display screens are now used. Several radioactive isotopes (forms) of strontium are produced by nuclear fission. They have uses both in the treatment of cancer and as power sources. Strontium salts are used in fireworks to give a deep red colour.
Sulphur can often be found around hot springs, volcanoes and fumaroles (holes in the ground through which steam and other gases...Read More >>Sulphur can often be found around hot springs, volcanoes and fumaroles (holes in the ground through which steam and other gases burst out). In these places, sulphur is released from under the ground in gases such as sulphur dioxide and hydrogen sulphide. When it reaches the colder surface, it solidifies.Sulphur (chemical symbol S; atomic number 16) is a non-metal. It is one of five non-metallic elements (along with carbon, iodine, phosphorus and selenium) that are solid at room temperature. Sulphur is soft and bright yellow, with a slight odour. It is common in the Earth’s crust in its elemental form—sometimes found on the surface, particularly around volcanoes—as well as in compound minerals.
Sulphur is essential for living things: it is found in vitamins, enzymes and proteins as well as in fuel for processes carried out by cells. Industrial uses of sulphur include the production of fertilizers, rubber, food preservatives, matches, antibiotics and pesticides.
Tin (chemical symbol Sn; atomic number 50) is a poor metal, also called a “post-transition metal”. Like other poor metals, tin is soft. It is silver-coloured, easily shaped and does not react quickly to oxygen or water, so it is slow to corrode. This makes tin useful as a protective coating for other metals. Tin is also less toxic (poisonous) than many metals, so it is often used for coating the inside of steel food cans.
Tin alloys include bronze (with copper), pewter (with copper, antimony and bismuth) and niobium-tin (used for superconducting wire). Tin’s relatively low melting point makes the metal, on its own or alloyed with other metals, useful for solders to fuse together metal pieces with higher melting points. Metallic tin does not occur in nature, but the element can be extracted from tin-containing minerals, such as cassiterite.
Tungsten, also known as wolfram (chemical symbol W; atomic number 74), is a transition metal. These metals are usually dense, shiny and make good electrical conductors. Tungsten has the highest melting point of all elements, at 3422°C (6192°F). It also has the highest tensile strength of all metals, meaning that it can be stretched to an extreme degree without breaking.
The very hard man-made compound, tungsten carbide (containing tungsten and carbon), is used for industrial cutting tools, ammunition and the rotating balls in the tips of ballpoint pens. Tungsten alloys are used for the filaments in light bulbs, electrodes and radiation shields. Metallic tungsten does not occur in nature, but the element can be extracted from minerals such as wolframite.
Uranium (chemical symbol U; atomic number 92) is one of the actinides, a group of radioactive metals. Uranium is the heaviest naturally occurring element available in large amounts. The atoms of a radioactive element are unstable: they are likely to break up. Radioactivity, also called radioactive decay, is the process by which the nucleus of an unstable atom loses energy by emitting particles or rays. Uranium is extracted from uranium-containing minerals such as uraninite.
The major use of uranium is in nuclear power plants, where its atoms undergo “fission”. This means that the nuclei of the atoms are split apart when hit by a neutron, causing them to break up other atoms' nuclei—a chain reaction. The energy released in this process, nuclear energy, is used to generate electricity.
Xenon arc lamp used in an IMAX cinema projector. The lamps are widely used in cinema projectors, searchlights and vehicle...Read More >>Xenon arc lamp used in an IMAX cinema projector. The lamps are widely used in cinema projectors, searchlights and vehicle headlights.
Xenon (chemical symbol Xe; atomic number 54) is a noble gas. Tiny amounts of xenon are present in the atmosphere. The gas is produced industrially by the distillation of liquid air. Like the other noble gases, xenon is an odourless, colourless gas when at room temperature and pressure. The noble gases all have the maximum number of electrons possible in the outer shell of their atoms. This makes them stable and non-reactive—they rarely bond with other elements.
Xenon can, however, form a few compounds, such as xenon difluoride, which is used to etch (cut into) silicon for use in electronic devices. Other uses of xenon include xenon arc lamps (in which light is produced by passing electricity through the gas), plasma displays (xenon and neon are converted into plasma by electrodes), excimer lasers (used in eye surgery) and general anaesthetics (xenon affects the nervous system).
Galvanized steel (zinc-coated) handrail. Steel, iron and aluminium are often galvanized through the process of hot-dipping, in...Read More >>Galvanized steel (zinc-coated) handrail. Steel, iron and aluminium are often galvanized through the process of hot-dipping, in which the metal is put into a bath of molten zinc. The end result is often “spangled”—with a sparkly, patchy pattern. Zinc (chemical symbol Zn; atomic number 30) is a transition metal. Like most transition metals, zinc is dense, shiny and a good electrical conductor. Zinc is key to the working of the human body, where it plays an essential role in the nervous reproductive systems. After iron, aluminium and copper, zinc is the world’s most commonly used metal. It is extracted from ores such as sphalerite (zinc sulphide).
Zinc’s major use is to “galvanize” steel and iron: to form a coating to protect them from corrosion (rust). As the zinc coating corrodes, it forms a layer of zinc carbonate, which then serves to protect the metal underneath. Zinc’s fairly low melting point (420°C / 787°F) makes it ideal for alloying with other metals, such as aluminium, since it then makes them easier to melt and mould. Zinc is also used as an anode in batteries, while zinc compounds are widely used in the chemical industry for products ranging from deodorants to dietary supplements.
Consultant: Nina Notman
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