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chlorine etc. Some elements have intermediate • Compare the texture and colour of the
properties between those of metals and non- material obtained by the groups.
metals, they are called metalloids; examples • Add carbon disulphide to one part of
are boron, silicon, germanium, etc. the material obtained. Stir well
and filter.
• Add dilute sulphuric acid or dilute
• The number of elements
hydrochloric acid to the other part of
known at present are more
than 100. Ninety-two elements the material obtained.(Note: teacher
are naturally occurring and the supervision is necessary for
rest are man-made. • this activity).
More to know • Eleven elements are in gaseous Now answer
Perform all the above steps with both
• Majority of the elements are
the elements (iron and sulphur)
solid.
separately.
state at room temperature.
• Two elements are liquid at
room temperature—mercury
and bromine.
groups look the same?
• Elements, gallium and cesium • Did the material obtained by the two
become liquid at a temperature • Which group has obtained a material
slightly above room with magnetic properties?
temperature (303 K).
• Can we separate the components of the
material obtained?
2.4.2 COMPOUNDS
• On adding dilute sulphuric acid or
A compound is a substance composed of two dilute hydrochloric acid, did both the
or more elements, chemically combined with groups obtain a gas? Did the gas in
one another in a fixed proportion. both the cases smell the same
What do we get when two or more elements or different?
are combined?
The gas obtained by Group I is hydrogen,
Activity ______________ 2.4 it is colourless, odourless and combustible– it
is not advised to do the combustion test for
• Divide the class into two groups. Give hydrogen in the class. The gas obtained by
5 g of iron filings and 3 g of sulphur Group II is hydrogen sulphide. It is a colourless
powder in a china dish to both
gas with the smell of rotten eggs.
the groups.
You must have observed that the products
Group I
• Mix and crush iron filings and obtained by both the groups show different
sulphur powder. properties, though the starting materials were
the same. Group I has carried out the activity
Group II
• Mix and crush iron filings and involving a physical change whereas in case
sulphur powder. Heat this mixture of Group II, a chemical change (a chemical
strongly till red hot. Remove from reaction) has taken place.
flame and let the mixture cool. • The material obtained by group I is a
Groups I and II mixture of the two substances. The
• Check for magnetism in the material substances given are the elements—iron
obtained. Bring a magnet near the and sulphur.
material and check if the material is • The properties of the mixture are the
attracted towards the magnet.
same as that of its constituents.
20 SCIENCE
Rationalised 2023-24
