| Natural and Processed Materials: |
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| Substances: Structure, properties and uses | |
Everything
is made from chemicals
People often believe, incorrectly, that chemicals
are always either dangerous, poisonous, acids, medicines or liquids. All
of these are chemicals, but there are many, many more chemicals. Everything
is made of chemicals. Air, water, rock, soil, living and non-living things
are all made of chemicals.
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Chemical Structure
and properties
The
structure of a chemical (substance) is determined by its three dimensional
arrangement of atoms. Water, a chemical substance, has two hydrogen atoms
attached to a single oxygen atom to form a V shape. Ice floats in water
and the oceans are salty because water has this shape. If water were 'straight'
and not shaped as a V, then ice would sink and the oceans would be fresh
water!
Diamonds are the hardest substances known and are valued
for their brilliant clear crystalline structure. Graphite is gray and
soft, used in pencils and as a solid lubricant. What do diamonds and graphite
have in common? They are both made only of carbon atoms - the only difference
is their structures. In the chemical world, structure is important.
Properties and
uses
Different
substances have different properties because of their different structures
and chemical composition. Substances are selected for different uses according
to their properties.
Diamonds are used on drill bits because they are the hardest substance
known. Glass is used in windows because it is transparent, but car bodies
are made of metal and not made of glass because they need to bend in a
crash.
Rubber
is used in balloons, because rubber stretches, while plastic is used to
make drink bottles because it can be molded to the shape and will not
break easily. Wood is used to make a stirring spoon because it is a good
heat insulator and will not conduct heat to your hand.
Coffee
cups are made of polystyrene because it is a good insulator of heat and
keeps the coffee warm. Glass is OK for cold drinks, but not hot drinks,
because glass is not a good insulator of heat.
Copper and aluminium are used in electrical wiring because they can be
easily drawn out into a wire and conduct electricity.
Links:
Element,
compound or mixture?
The
three states of water - "the water cycle"
Solutions
The
liquid state
Metal
and non-metals
Properties
of metals
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