Page 40 - Science Class 08
P. 40
not contain other minerals, though they do refined, i.e., purified. At the same me
contain impuri es like soil or sand. The some substances are added to the refined
scien fic name for these impuri es is gangue. metal in order to give it the desired
Other metals occur in nature in the form of proper es.
compounds— oxides or sulphides. An oxide is a PHYSICAL PROPERTIES OF METALS
compound of a metal and oxygen while a Metals display some physical and chemical
sulphide is a compound of a metal and sulphur. proper es that can be studied one-by-one.
A third category of metals is called the silicate
Physical State
metals. These metals occur in combina on
with silicon and oxygen. All metals except mercury exist in solid state at
ordinary temperature. So, they are able to retain
Silicate metals are found in the rocks of the
their definite shapes in normal condi ons. Most
earth’s crust. As these rocks are very hard,
metals have very high mel ng points.
their extrac on in pure state from silicates is
very difficult as well as costly. For example, iron melts at 1535°C while copper
melts at 1083°C:
EXTRACTION
Luster
Man had discovered technology of obtaining
metals from their ores right in very ancient Most metals have a shiny look (appearance)
mes. Several processes have to be carried out especially when they are cut. This shine is
to obtain a metal from its ore and then purify called metallic lustre. It makes metals useful in
it. This technology has developed in a full- decora on, in jewellery, etc.
fledge science, called metallurgy. Malleability
Metallurgy is the branch of science that studies Metals are malleable in general. It means that
metals and the technology to extract them as they can be beaten into thin sheets. You must
well as purify them. have seen iron-smiths bea ng iron into sheets
The scien sts who study this science are called for various purposes.
metallurgists. Three opera ons have to be Duc lity
performed to obtain pure metals. All metals are duc le as well. It means that
These three opera ons are as under: they can be drawn into wires. Wires of copper,
v Concentra on of the Ore : It is the first and iron and aluminium can be seen anywhere
elementary opera on that aims at remo- around. All electric wires have copper threads
ving impuri es by concentra ng, i.e., by inside them. The filament of an electric bulb is
removing moisture etc., out of it. made of tungsten wires. Wire-gauzes and
barbed wires etc. are made up of iron wires.
v Reduc on : It is the second opera on that
reduces the metal-compound by removing Conduc vity
its oxygen or sulphur, etc. in order to get If one end of a metal rod is put in hot water,
the metal in its free state. the other end will also become hot in a minute
v Refining the Metals : This is the third and or so. Clearly, metals can conduct heat very fast
last opera on in which the free metal and easily. Gold is the best conductor of heat
obtained a er reducing the compound is followed by silicon, copper and aluminium.
40 Science-8
