SEE FOR YOURSELF
Try bending a wire paper clip to and fro until it eventually breaks. You will notice that the wire is quite soft at first. But as you continue to bend it, it gets harder. Eventually a crack forms and the wire snaps.
Repeated bending upsets the regular arrangement of the atoms inside the metal wire. Faults called dislocations appear in the layers of atoms. These dislocations stop the layers sliding so freely and the metal becomes brittle. Scientists say that the metal is fatigued. Some of the first jet airliners crashed because certain components failed as a result of metal fatigue.
|A football made from osmium, the heaviest metal, would weigh 160kg - as much as two adult football players!|
There are more than 100 elements in the Periodic Table, and more than 75% of these are metals. Six metallic elements - aluminium, iron, calcium, sodium, potassium, and magnesium - are the most abundant elements in the Earth's crust, after oxygen and silicon. Many other metals are present in smaller quantities.
Metals are among the most useful of all materials. Steel cars and ships, aluminium aircraft, copper cables, silver cutlery, mercury batteries, platinum catalysts, lead roofing, gold teeth, titanium bicycles - the variety of uses to which metals are put is enormous.
is a metal?
Nearly all metals are heavy materials. Lead is 11.3 times denser than water, mercury 13.6 times more dense, and osmium, the heaviest metal, a massive 22.5 times denser. But lithium, the lightest metal, is only just over half as dense as water, so it floats. However, the key quality of a metal is that one or more electrons can escape easily from its atoms. Inside a piece of metal, electrons that have broken away from the atoms move around freely, almost like the molecules in a gas. It is these electrons that carry heat and electricity so efficiently through the metal.
Pure metals are ductile - they can be stretched (drawn) into wires and pipes. They are also malleable - they can be beaten into sheets and other shapes. Pure gold is so malleable that it can be beaten into sheets finer than a human hair. This so-called gold leaf is used to decorate books and china.
Pure metals are soft because of the way metals atoms are arranged. Metal atoms are packed together closely in very regular sheets, rather like stacks of marbles or snooker balls. Six others in the same sheet surround each atom. The sheets of atoms can slide across each other easily, so the metal changes shape when a force is applied. But the strong electric force between the atomic nuclei and the free electrons stops the atomic sheets coming apart, giving the metal strength.
Steel is an alloy of iron and carbon. The hardness of steel can be adjusted by altering the amount of carbon it contains, and by heat treatment. Heating and cooling the steel changes the way the carbon is distributed through the structure. Cutting tools are hardened by heating them, then cooling them rapidly in an oil bath.
At the top of the list are the alkali metals, which include sodium and potassium. They are very reactive, and burn or explode on contact with water. For this reason, they have few practical uses in pure state. Following them are the other metals that combine readily with non-metals, though usually much less vigorously. These include calcium, magnesium, aluminium, zinc, iron and lead. At the bottom of the list are the noble metals, copper, silver and gold. They form compounds only very reluctantly.
There are many causes of corrosion. Steel ships are corroded by salt water, and copper domes by fumes from coal fires and car exhausts. Even silver tarnishes with age, and must be polished to restore its shine.
IRON - Iron is a dense, silver-gray metal. It is the most widely used of all metals. Steel, an alloy of iron and carbon, is used to build car bodies, bridges and ships.
ALUMINIUM - Aluminium is a light, silver-white metal. It is the second most widely used metal, and is particularly useful when a light material is needed, for example in aircraft components and lightweight ladders.
COPPER - Copper is a soft, reddish-yellow metal. It is valued for its high electrical and heat conductivity, and for the ease with which it can be drawn into pipes and wires.
ZINC - Zinc is a weak, gray metal. When a sheet of iron is coated with a thin layer of zinc - a process called galvanation - the zinc protects the iron from corrosion.
BRASS - Brass is an alloy of copper and zinc that is stronger and more corrosion-resistant than either metal on its own. It is used to make fittings for ships, as well as small bells and ornaments.
TIN - Tin is a bright, silver-coloured metal; 'Tin' cans are made from steel coated with a thin layer of tin to protect the steel from corrosion.
LEAD - Lead is a dense, soft, gray metal. It was once used to make water pipes, but has been replaced because it is so poisonous. Solder is a tin-lead alloy with a low melting point. It is used to join electronic components.
TITANIUM - Titanium is a light, strong, silver-white metal. It is used in high strength alloys in jet engines and artificial joints. The Apollo space capsules were made mainly from titanium.
NICKEL - Nickel is a hard, silver-coloured metal that can be highly polished. It is added to steel to give increased strength. A nickel-copper alloy is used to make 'silver' coins.
TUNGSTEN - Tungsten is a brittle, gray metal with a very high melting point. Its main use is in the filaments of light bulbs. These glow brightly at a temperature of about 3000'C.
CHROMIUM - Chromium is a bright, silver-coloured, corrosion-resistant metal. Car parts were often chromium-plated in the 1950s and 1960s to protect them from rust. Stainless steel contains about 10% chromium to prevent rusting.
Look out for the "Did You Know?"s and "It's Amazing"s throughout your journey in the mysterical world of physics.
|A craftswoman applying fine gold leaf to
an ornamental wreath. This technique, called gliding, is possible because
of gold's extreme malleability - its capacity to be hammered into thin,
The electrons from the outer shells of metal atoms move around freely, in a kind of 'sea'. As a result, they can carry heat and electricity through the metal. Because the negatively charged electrons are not attached to individual atoms, the atoms become positively charged ions, and the electrons and ions are held together by electrical attraction. This link between metal atoms is called metallic bonding.
This old steam engine is covered in rust, which
forms when iron reacts with water and oxygen in the air. If rust is left untreated,
the original metal will eventually be destroyed completely.