Solids show specific properties due to definite arrangement of atoms, ions and molecules. Basic properties of solids are discussed below
1. Melting points:
Solids possess sharp
melting points and due to this property identification of specific solids can
be done on the basis of their melting points.
2. Geometry:
Atoms, ions and molecules in solids usually align in
a three dimensional ordered arrangement which give rises to definite shape and
geometry. The interfacial angle of a given crystal at which intersect with
surface takes place is always same for all the geometrical shapes. The angles
and faces do not change even after the crystalline solids are being grounded.
3. Symmetry:
The phenomenon to repeating angles, edges and faces due
to rotation at 360o is known as symmetry of solids. The symmetry
elements of a specific solid are characteristic features of that solid. These elements
include center of symmetry, plane and axis of symmetry.
4. Cleavage planes:
Crystalline solids always break along definite
planes and inclined to each other at a specific angle in a crystal system. These
planes are named as cleavage planes and this angle is specific for each solid.
5. Habitat of a crystal:
Crystalline solids grow in definite shape and this
shape is called habitat of that crystal. Crystals grow when a saturated
solution is cooled or a liquid substance is cooled slowly. The crystals can
grow in divergent directions giving rise to various shapes. Crystal growth
depends upon the conditions provided and the shape of a crystal always remained
same at constant conditions which can otherwise changed on changing the
provided conditions. For instance, sodium chloride possesses a cubic structure
in normal conditions but it changes to a needle like structure on adding 10%
urea in the solution of NaCl.
6. Anisotropy:
The variation of physical properties of crystalline
solids on the basis of direction is specifically known as anisotropy and these
properties are categorized as anisotropic properties. Anisotropic properties
include coefficient of thermal expansion, refractive index and thermal or
electrical conductance.
7. Allotropy:
Some elements possess more than one crystalline
forms of same element. This phenomenon is called allotropy and the crystalline
forms are known as allotropic forms of that element. For example, diamond, graphite
and coal are three natural allotropes of carbon while graphene is fourth
synthetic allotrope of carbon.
8. Polymorphism:
The existence of a compound in more than one
crystalline form is known as polymorphisms and different forms of crystal are
called polymorphs. Solids that show this property are specifically known as
polymorphic compounds. Polymorphic compounds possess same chemical but
different physical properties.
9. Isomorphism:
The existence of two divergent substances into same
crystalline form is known as isomorphism. The two substances that exist in same
crystalline for are isomorphs of each other. Crystalline system depends upon
the number and arrangement of atoms within the crystal system and does not
depend on chemical properties of these atoms.
10. Transition temperature:
The temperature at which two crystalline forms of
same substance coexist in equilibrium is known as transition temperature. One crystalline
form of a solid diverts to other crystalline form at transition temperature. For
example tin shows grey color in cubic form while it turns white at 13.2 oC
on converting in tetragonal form.
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