Page 51 - Science Class 08

v It is highly malleable and duc le. proper es, though they appear like metals.
v Even strong acids can’t do any harm to it.
v It does not corrode or tarnish in air.
v It can dissolve in aqua regia.
v It combines with phosphorus, silver and
arsenic quickly.
v It can form alloys with many metals –
nickel, iridium etc.
Use of Pla num
This metal is used as under:
v Containers made of pla num are used in
chemical laboratories as it resists the
a acks of heat and chemicals.
v Several equipments have their parts made
of pla num – nibs of pens, jewellery, etc.
v Pla num is an effec ve catalyst.
v It can change certain pollutants into non-
pollutants.
v It is used for frac onal break-up of
petroleum to get various by-products while
refining petroleum.
v It is used to make nitric and ace c acids.
v It is used to make moulds for ornaments
and fibre glass.
v Due to its colour, strength and hardness, it
is used in gem-cu ng and for surgical
instruments.
v Pla num-iridium alloy makes the best
surface for engraving.
v It is used to make finer measuring devices
and weights.
v Its salts are used to treat cancer and in
photography.
NON-METALS
Before studying non-metals, we must know
that there are elements that stand in-between
the metals and non-metals in terms of
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Such elements are called metalloids. Silicon,
germanium and boron are three common
examples of metalloids. We shall read about
them in higher classes.
As for non-metals, they have their own
proper es that are opposite to those of metals.
Let us read about them in detail:
Non-metals are the elements which can form
nega ve ions by gaining electrons.
For example, oxygen is a non-metal because it
2-
can form nega ve ion (O ) by gaining two
electrons. In the same way, hydrogen, carbon,
sulphur, silicon and phosphorus are also non-
metals because all these elements can form
nega ve ions by gaining electrons.
Unlike metals, the oxides of non-metals are
acidic or neutral in nature. There are 22 non-
metals. At room temperature, non-metals exist
in solid, liquid as well as in gaseous form. Out
of 22 non-metals 10 non-metals are solid 8
(e.g., carbon, sulphur and phosphorus), 11 non-
metals are gases (e.g., hydrogen, nitrogen,
oxygen and chlorine), whereas only one non-
metal (bromine) is a liquid non-metals.
OCCURRENCE
Some non-metals occur in a free state. Such
non-metals include noble gases – helium, neon,
argon, xenon and krypton. They occur in their
elemental form in air, but in very small
quan es. Nitrogen and oxygen too occur in
the air in their elemental form. But, they are
found in the form of compounds as well just
like sulphur.
All other non-metals occur in a combined state
with other metals and non-metals iodine,
bromine, chlorine, carbon and fluorine and
other common non-metals. In all non-metals
are around twenty in number.
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