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Elements are substances that are made up of only one kind of atom.
Gold is an element; at the smallest level it is made from atoms of gold and nothing else. Other elements are Hydrogen, Iron, Oxygen and Silicon.
In ancient times, people thought that everything in the world was made up of only four elements: fire, earth, air and water.
Water, however, is not an element. Water is made up of molecules containing atoms of Hydrogen and Oxygen.
Water is a compound. Its molecule contains 2 atoms of Hydrogen and 1 of Oxygen, giving the famous formula
Other compounds are table salt, sugar, and ammonia.
A compound can be very different to the atoms that make it up. Table salt is sodium chloride. Its smallest unit is an atom of sodium and an atom of chlorine. Sodium is a soft reactive metal. Chlorine is a pale yellow poisonous gas. Combine them together and you get a colourless crystalline solid that is essential for life.
Atoms are composed of a dense nucleus containing protons (positively charged particles) and neutrons (uncharged particles). The nucleus is surrounded by electrons (negatively charged).
The outer electrons of an atom determine its physical properties (colour, melting point, etc) and its chemical properties (which other atoms it combines with and how easily and the fact that one oxygen atom combines with two hydrogen atoms to form water).
In a normal atom the number of protons is equal to the number of electrons. This is called the ATOMIC NUMBER. The simplest atom is Hydrogen with an atomic number of 1.
In this section, I will introduce some of the better known elements in general terms. Each element is given along with its symbol. This is either a single capital letter (O for oxygen, C for carbon) or a pair of letters, the first capital and the second lower case (Ca for calcium, Si for silicon). These symbols are internationally recognised. they are not abbreviations so do not require dots, full stops (periods) after them.
The description of physical properties is assumed to be at normal (surface of the Earth) pressures and temperatures.
If the gas is placed in a glass tube and has an electric current passed through it, the tube glows with an orange-red light. The colour of the light may be changed to blue or green by the addition of Mercury. These Neon Lights are used in advertising.
Sodium is not found in its elemental state on Earth but its compounds are common.
Its most useful compound is common salt (Sodium Chloride - NaCl), essential in the nervous systems of animals. Sodium Hydroxide (NaOH - better known as Caustic Soda) is an important industrial compound. Other compounds are used in the production of petrol additives for cars, and the manufacture of glass, paper and soaps.
The Sodium atom absorbs and emits light in the yellow part of the spectrum, hence the colour of Sodium (street) lights.
The name comes from soda (NaHCO3) which is used in cooking. The symbol Na comes from its Latin name Natrium.
Magnesium is a light silvery-white metal that burns with an brilliant white flame. It is stable in air if not ignited but reacts with boiling water.
It was once used for illumination in theatre and photography. It is used in alloys where lightness and strength is important. Its compounds are used in medicine, dying, cement and in the manufacture of cotton goods.
Its importance in life is that it occurs in Chlorophyll (Greek for green leaf). This is the substance that allows plants to convert sunlight into sugars at the beginning of the food chain.
It is the most common metal on the Earth's crust, a common component of most rocks. The Sapphire and Ruby are forms of Aluminium Oxide (Al2O3). They are used as abrasives and in jewelry
Its compounds are used in paper making, dying, medicine, organic synthesis and enamels. .
It is element 13.
Silica is a component of all rocks along with Aluminium and other less common elements. Sand is almost pure Silica as are glass, flint and quartz.
The element itself does not occur naturally and is difficult to extract. Once produced it is fairly stable. It resembles a hard, grey, metallic rock.
It is used extensively in the computer industry and used for converting sunlight into electricity in light cells.
Some have suggested the existence of Silicon based life because Silicon forms many compounds, especially with Hydrogen. These compounds are all unstable under normal conditions; rocks are the most stable kind of silicon compounds.
Phosphorus has two allotropes. Yellow Phosphorus (also known as White Phosphorus) is a soft, waxy, translucent solid that glows when exposed to air and is highly poisonous. It is normally stored under water. Red Phosphorus is a non-poisonous brittle solid that does not react with air unless ignited. The red form is used in matches.
Phosphorus occurs in organic compounds in certain proteins, and is an important constituent of bones and teeth. It is also found in guano (bird waste) which is often used as a fertiliser.
It also has a controversial use as a military weapon.
The element occurs as several allotropes differing in crystal structure. Rhombic Sulphur is a yellow, brittle solid that melts at 113°C. Monoclinic Sulphur occurs as fine light yellow needles with a melting point of 119°C. A plastic, amorphous form also exists. All forms burn in air with a blue flame producing noxious gases.
Sulphuric Acid (H2SO4) is a very important industrial compound. The element and its compounds are very important in the processing of rubber and the manufacture of wood pulp, dyes, rayon, insecticides, fungicides and anti-biotics.
Sulphur occurs in certain proteins (egg yolk). This is element 16.
Chlorine is a Halogen. It is found in common salt (NaCl).
Its organic compounds are mainly used as industrial solvents, cleaners (like bleach), and pesticides (like DDT). Hydrochloric acid is an important industrial chemical and has the formula HCl.
It is element No 17.
It is used in neon lights where it gives a lilac to blue colour. However, it is less luminous than Neon. It is used extensively in electric light bulbs as it provides an inert atmosphere for the glowing filament.
Potassium (an Alkali Metal) is a very soft, silvery-white metal. It is stable in dry air but corrodes rapidly in the presence of moisture. It reacts violently with water, liberating Hydrogen which bursts into flame due to the heat of the reaction.
Its compounds are used in medicine, fertilisers, explosives and photography.
Calcium is found in many minerals including Calcium Carbonate (CaCO3). This occurs as chalk, limestone and marble. Dolomite is a mixture carbonates (MgCO3.CaCO3). Calcium Suplhate (CaSO4) occurs as alabaster and gypsum. Another form is Plaster of Paris, used for moulds and casts. Fluorspar is Calcium Fluoride (CaF2).
Lime is Calcium Oxide (CaO). Heating Lime with Coke in a furnace produces Calcium Carbide (CaC2), a greyish black sold that gives flammable acetylene gas when water is added. It was once used to illuminate the stage in theatres. This is the origin of the phrase in the lime light.
Calcium is present in living material such as bones, teeth (mainly Ca3(PO4)2) and shells (also CaCO3).
Compounds of Calcium are used in the manufacture of glass, steel, paper and in sewage treatment.
It is Element No 20.
Titanium Carbide (TiC) is a hard solid used in tool tips. Titanium Oxide (TiO2) is a brilliant white pigment used in house paints. Other compounds are used in smoke screens.
It is used as a protective coating to many metals due to its resistance to oxidation. It is added to Iron in the making of steel, providing corrosion resistance and hardness.
Chromium compounds are used for making pigments and as laboratory reagents.
Its alloys are used to toughen steel and are used for rock crushers, railway points and in engineering.
Manganese compounds are useful laboratory reagents (like Potassium Permanganate, KMnO4) and catalysts (like Manganese Dioxide, MnO2).
The name comes from an old English word.
Iron has been an important metal historically, being known in the ancient Middle East. It has the rare property of magnetism. Its oxides (rust) are red. Mars has lots of rust on its surface, hence its red colour. Iron is an important constituent of haemoglobin in mammalian blood. Its compounds are used as paint pigments and in medicine.
The metal itself is made by mixing its ores with coke (Carbon) and roasting in air in a Blast Furnace. Depending on the exact process used, this forms Cast Iron (a gray metal melting at 1200°C) or Wrought Iron (a tough, malleable metal melting at 1500°C but softening at 1000°C). The addition of Carbon and other metals produces the corrosion resistant steel.
Iron and steel are the basis of much of civil engineeering: bridges, buildings, tunnel lings, engines, vehicles, machine tools, surgical instruments, springs, ball bearings, valves and household items.
Its Atomic Number is 26. The symbol Fe comes from the Latin name for the metal, Ferrum.
When finely divided it absorbs 100 times its volume of Hydrogen; this makes it useful as an industrial catalyst. Its alloys are used for high temperature components and in magnets.
The compounds of Cobalt are often intensly coloured: blues, pinks and yellows that are used as pigments. Other uses: special glasses, ceramics, magnets and razor blades. A radioactive form (Cobalt-60) is used in cancer therapy.
The name is from the German kobold (evil spirit).
It is a hard silvery-white metal (melting point: 1453°C) used in electroplating and as a catalyst. Its alloys are used in batteries, coinage, metal-glass seals, clocks, thermostats and electric heaters.
Copper occurs in its elemental state and has been used since 4000BC. The metal is an excellent conductor of both heat and electricity. It is used extensively in the electricity industry: most house wiring is Copper. Its alloys include bronze and brass. It is also used in coinage.
Copper compounds are used in agriculture, water treatment and wood preservation. The Copper atom occurs in the blood of crustaceans.
Its alloys are used to coat steel in a process called galvanising. It is used in making car acessories and toys.
Zinc compounds have extensive uses including fire-proofing textiles, ceramics, wood preserving, batteries, dentistry, rust-preventing pigments, fungacides, plastics, bleaching, surgical dressings and as dehydrating agents.
It is element number 30.
It is a silvery-white metal with the lowest melting point after Mercury. It melts at 30°C, so body heat will melt it. It boils at 2230 °C so it is used for high temperature thermometers.
Its alloys are used in transisters and printed circuits as it is semi-conductor. A semi-conductor has a low electrical conductivity that varies with temperature and other factors.
Gallium is element number 31.
It is a dark grey, brittle semi-conducting solid. It is used in transisters and other electronic devices. It melts at 937°C.
Its alloys expand slightly on cooling and are used in small scale precision casting.
Its compounds are famous as poisons but are also used in medicine, semi-conductors and in pigments.
The name comes from Arsenicos, Greek for male.
The metallic allotrope conducts electricity; the condictivity increases with the amount of light present. This property finds uses in photo-electric cells, light sensors and photocopiers.
Selenium compounds are used for tinting glass and in fungicides, herbicides and explosives.
It is element number 34.
The element is very reactive. Its compounds are used as sedatives, in organic synthesis and for the extraction of gold.
It is another of the Halogens (salt formers). It is element number 35.
Its alloys are used to can nuclear fuel rods because the metal absorbs few neutrons.
Zirconium Oxide (ZrO2) is used for making crucibles for high temperatures.
Molybdenum is added to alloys to make them hard and wear-resistant for cutting tools. Its compounds are used in ink, dyes and enamels.
The metal is pure white, malleable and ductile. It can be beaten into very thin leaves. its melting point is 961°C. Its main uses are jewellry, cutlary, electrical work, coinage, as a catalyst and in medicine.
Many Silver compounds are sensitive to light; they are used in black and white photography.
Its alloys are used in electric batteries and overhead wires for trains and trams. Its compounds are used in fireworks and as ceramic pigments.
Cadmium is element 48.
At ordinary temperatures, Tin is a white lustrous metal. It is harder than Lead and can be rolled into sheets. At temperatures below 13°C, the metal slowly changes into a second allotropic form, Grey Tin which is brittle. This causes tin roofs to decay at very low temperatures.
The alloys of Tin include Bronze, solder, pewter and gun-metal.
Tin is used for coating other metals to stop them corroding (tinning). "Tin" cans are made from tinned Iron.
Physically it resembles the metals being a bluish-white, lustrous solid. Chemically it resembles the non-metals, forming acids and liquid compounds with the Halogens. Below -90°C it exists as a yellow allotrope.
It has been known since 3000BC when used as an eyebrow pigment. It is also used in alloys (like pewter and bearing metals).
Iodine dissolves in alcohol to give Tincture of Iodine, used as a disinfectant. Its compounds are very important in medicine.
Being a Halogen, many of its compounds are crystalline solids.
The name comes from the Greek for violet.
It is added to alloys and used in medicine, pigments, fine glassware and ceramics.
It is a very hard, grey metal with a high melting point (3370°C). Its alloys are very resistant to wear and heat and are used in light bulb filaments, electrical contacts and high speed cutting tools.
Tungsten Carbide (WC) is a very hard substance used for making drilling tools.
Its alloys are used in applications dependent on hardness and inertness and its compounds are used as catalysts.
Platinum is one of the noble metals, very few chemicals corrode it or react with it. Its main uses are jewellery, as an industrial catalyst and in high quality electrical equipment. It has an Atomic Number of 78.
Its major use today is for a monetary standard. There are some uses in electronics.
Its Atomic Number is 79. The Latin name was Aurum, from where the symbol arises.
It is a dense substance whose properties are used for making thermometers (from the Greek for measure heat) and barometers (from the Greek for measure weight).
It is an accumulative poison associated with an incident in the village of Minimata in Japan. During the 1960s, industrial discharges of Mercury into the sea ended up in the fish that the local population ate. The result was Minimata Disease which caused people to lose control of their nervous system. It is element No 80.
The Latin name Hydrargentum (water silver) gives the element its symbol.
It is a silvery white metal that rapidly turns grey in air due to a layer of oxide that protects the metal from further attack. It melts at 327°C. It is a dense metal. It is used in car batteries, cable covering and building.
Many of its compounds are poisonous. They are used in paint pigments, explosives and as laboratory reagents.
Lead is almost the most complex atom that can be stable.
The metal is used in atomic reactors. Its alloys tend to have low melting points (often below 100°C) and are used for fuses, solders, and fire protection devices.
Its compounds are used in medicine and for making stained glass.
Bismuth is element number 83. Atoms with larger Atomic Numbers than Bismuth are unstable. Bismuth is the heaviest of the stable atoms.
The nucleus of the Radium atom slowly breaks down by ejecting bits and changing to an element with a lower Atomic Number. This process is called Radioactivity. The element Radium is said to be Radioactive. The radiations given out are usually dangerous to living organisms because they can damage the delicate molecules of life.
Radioactivity is unaffected by physical conditions like temperature or pressure. It is also unaffected by chemical properties so that Radium compounds are as unstable as the element itself.
If a lump of Radium is allowed to stand, its atoms will change to other types of atoms. After 1622 years half of the original amount of Radium will be left. This is called the Half-Life of Radium. Each type of radioactive element has its own specific Half-Life.
The period of 1622 years is very short compared with the age of the Earth. All the Radium on the Earth has been produced by the radioactive decay of even heavier elements like Thorium and Uranium.
Chemically, Radium is a white metal that tarnishes in air and reacts with water. Its compounds appear luminous in the dark because of the radioactivity and were once used in luminous watch dials. They are now used in medicine as a source of Gamma Rays.
The Uranium nucleus will, of course, no longer be Uranium, as its Atomic Number will have decreased by 2. It will now be an element called Thorium which is element number 90 and is itself radioactive. Radioactive elements keep decaying until a stable nucleus like Lead or Bismuth is reached.
The Half-Life of Uranium is over 5,000 million years. This is older than the age of the Earth. Radioactive elements can be used for dating rocks because the rate of decay is constant and independent of physical conditions like temperature or pressure.
Some Uranium atoms are different to the one described above. They still have 92 protons (otherwise they would not be Uranium) but they only have 143 neutrons. The 146 neutron variety is called Uranium 238 (because 92 and 146 = 238). The first variety is called Uranium 235 (92 + 143 = 235). Many elements have atoms which only differ in the number of neutrons, these are called isotopes, from the Greek for same place because they are found together and are tabulated together as a single substance.
All isotopes have the same chemical properties. The chemistry of atoms is determined by the arrangement of electrons around the nucleus. These two types of Uranium cannot be distinguished by chemical means. However because the two types of atoms differ in mass (235 and 238 times the mass of a Hydrogen atom respectively) they can be separated by physical methods. One way is to produce gaseous compounds (like Uranium Hexafluoride, UF6) and allow them to diffuse through a number of barriers. The heavier molecules diffuse at a slower rate.
The interesting thing about Uranium 235 is the behaviour of its nucleus when it is struck by a neutron.
The nucleus splits into two.
This is called nuclear fission. The break up of the nucleus releases vast amounts of energy and produces nuclei around Atomic Numbers 40 to 50 as well as free neutrons. These free neutrons can initiate more fission reaction, and so on. This process is called a chain reaction and is the basis of the atom bomb and most nuclear power stations.
The element was discovered shortly after the planet Uranus and was named after it. It is a reactive metal, tarnishing rapidly in air.
This element is not normally found in nature but is produced artificially. It is now a by-product from Uranium power stations. Like Uranium 235, its nucleaus can undergo fission and so is used as a nuclear fuel.
Plutonium, however, is one of the most poisonous substances known.
© 2005, 2013 KryssTal
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An excellent site featuring an interactive periodic table. Click on each element to reveal a wealth of information, including graphs. Also a chemical dictionary.
An excellent chemistry site for young people and beginners.