Types of solids
Solids can be generally classified into following two types,
(i) The Crystalline solids/True solids,
(ii) The Amorphous solids/Pseudo solids
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Crystalline solids
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Amorphous solids
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They have long range order.
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They have short range order.
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They have definite melting point
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Not have definite melting point
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They have a definite heat of fusion
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Not have definite heat of fusion
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They are rigid and incompressible
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Not be compressed to any appreciable extent
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They are given cleavage i.e. they break into two pieces with plane surfaces
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They are given irregular cleavage i.e. they break into two pieces with irregular surface
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They are anisotropic because of these substances show different property in different direction
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They are isotropic because of these substances show same property in all directions
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There is a sudden change in volume when it melts.
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There is no sudden change in volume on melting.
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These possess symmetry
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Not possess any symmetry.
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These possess interfacial angles.
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Not possess interfacial angles.
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(2) The crystalline and amorphous silica
Silica occurs both in the crystalline as well as amorphous states. Quartz is a typical example of the crystalline silica. Quartz and the amorphous silica differ significantly in their properties.
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Quartz
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Amorphous silica
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It is crystalline in nature
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It is light (fluffy) white powder
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All four corners of tetrahedron are shared by others to give a network solid
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The tetrahedra are randomly joined, giving rise to polymeric chains, sheets or three-dimensional units
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It has high and sharp melting point (1710°C)
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It does not have sharp melting point
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(3) Diamond and graphite
The diamond and graphite are two allotropes of the carbon. Diamond and graphite are both covalent crystals. But, they differ significantly in their properties.
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Diamond
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Graphite
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It occurs naturally in free state
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It occurs naturally, as well as manufactured artificially
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It is the hardest natural substance known.
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It is soft and greasy to touch
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It has high relative density (about 3.5)
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Its relative density is 2.3
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It is transparent and has high refractive index (2.45)
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It has black in colour and opaque
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It is non-conductor of heat and electricity.
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Graphite is a good conductor of heat and electricity
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It burns in air at 900°C to give CO2
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It burns in air at 700°C to give CO2
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It occurs as octahedral crystals
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It occurs as hexagonal crystals
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(4) Classification of the crystalline solids
Table : 5.1 Some characteristics of different types of the crystalline solids
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Types of Solid
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Constituents
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Bonding
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Examples
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Physical Nature
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M.P.
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B.P.
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Electrical Conductivity
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Ionic
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Positive and negative ions network systematically arranged
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Coulombic
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NaCl, KCl, CaO, MgO, LiF, ZnS, BaSO4 and K2SO4 etc.
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Hard but brittle
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High (?1000K)
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High (?2000K)
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Conductor
(in molten state and in aqueous solution)
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Covalent
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Atoms connected in covalent bonds
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Electron sharing
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SiO2 (Quartz),
SiC, C (diamond),
C(graphite) etc.
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Hard
Hard
Hard
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Very high (?4000K)
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Very high
(?5000K)
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Insulator except graphite
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Molecular
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Polar or non-polar molecules
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(i) Molecular interactions (intermolecu-lar forces)
(ii) Hydrogen bonding
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I2,S8, P4, CO2, CH4, CCl4 etc.
Starch, sucrose, water, dry ice or drycold (solid CO2) etc.
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Soft
Soft
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Low
(?300K to 600K)
Low
(?400K)
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Low
(? 450 to 800 K)
Low
(?373K to 500K)
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Insulator
Insulator
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Metallic
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Cations in a sea of electrons
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Metallic
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Sodium , Au, Cu, magnesium, metals and alloys
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Ductile malleable
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High
(?800K to 1000 K)
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High
(?1500K to 2000K)
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Conductor
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Atomic
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Atoms
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London dispersion force
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Noble gases
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Soft
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Very low
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Very low
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Poor thermal and electrical conductors
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