1.1 Introduction : As studied earlier, the solid
state of matter is characterised by strong
interparticle forces of attraction. As a result
most solids have definite shape and volume,
which change only slightly with change
in temperature and pressure. The smallest
constituent particles of various solids are
atoms, ions or molecules. All such smallest
constituent particles of solids will be referred
to as 'particles' in this chapter.
1.2 Types of solids : There are two types
of solids, namely crystalline solids and
amorphous solids.
- SOLID STATE
Can you recall?- What are the three most common
states of matter? - How does solid state differ from the
other two states? (Answer with reference
to volume, shape, effect of temperature
and pressure on these and the motion
of constituent particles and interparticle
forces.)
1.2.1 Crystalline solids : Study of many
crystalline solids indicates that they possess
the following characteristic properties.
i. There is a regularity and periodicity in
the arrangement of constituent particles in
crystalline solids. The ordered arrangement
of particles extends over a long range.
ii. Crystalline solids have sharp melting
points, that is, they melt at a definite
temperature.
iii. All crystalline substances except those
having cubic structure are anisotropic. In
other words their properties like refractive
index, thermal and electrical conductivity,
etc, are different in different directions.
Ice, salts such as NaCl, metals such
as sodium, gold, copper and materials such
as diamond, graphite, ceramics are examples
of crystalline solids.Observe and discuss...- Collect the following solids :
grannular sugar, common salt,
blue vitriol. - Observe a few grannules of these solids
under a magnifying lens or microscope. - Discuss your observations with reference
to the following points : (i) Shape of the
grannules, (ii) Smoothness of faces of
the grannules and (iii) Angles between
various edges of the grannules. - All the above solids are crystalline solids.
Name the properties of crystals that you
observed in this activity.
Try this...Observe the above figure carefully.
The two types of circles in this figure
represent two types of constituent particles
of a solid.- Will you call the arrangement of particles
in this solid regular or irregular? - Is the arrangement of constituent
particles same or different in directions
→
AB,
→
CD, and→
EF?