________________
(b) सभी धातुएं सामान्य तापमान पर घन या ठोस रूप में होती हैं। (केवल पारा इसका
अपवाद है।) ठोस पदार्थों में जो स्फटिक रूप है, उनकी विशेषताएं इस प्रकार बताई गई
61, q. 1259"Solids All solids have the property of elasticity and by virtue of this property, the solids behave as in compressible substances and exhibit rigidity and the mechanical strength. Basically, all solids are made of atoms and molecules but due to the different internal arrangement of the molecules inside them, they are divided into two classes, namely crystalline and amorphous materials. Crystalline Materials The crystalline materials are those in which atoms or molecules are arranged in a definite and regular way troughout the body of the crystal and possess a definite external geometrical shape. A few examples of crystalline substances are quartz, mica, sugar, copper sulphate, sodium chloride etc. The crystalline substances have the following characteristics : 1. The atoms or molecules constituting a crystalline solid are
arranged in a definite and regular manner inside the crystal. Due to this, crystalline materials have definite external geometrical shape. The orderly arrangement of atoms and molecules in a crystal extends over a large volume of the crystal i.e. crystals exhibit
a long range order of the atoms and molecules. 3. Crystalline substances are bounded by flat sufraces.
Crystalline substances are anisotrophic i.e. the physical properties like thermal conductivity, electrial conductivity, compressibility, etc. have different values in different
directions. 5. Crystalline materials possess uniform chemical composition
i.e. bonds between all the ions, atoms or molecules are of
equal strength. 6. A crystalline material has a sharp melting point. It is because,
all the bonds between its constituents are of equal strength; and on heating, all the bonds get ruptured suddenly at a fixed temperature. Due to this, the change from solid state
to the liquid state occurs suddenly. 7.
Below the temperature of crystallisation, the crystalline materials are in stable state. Since a stable state is the state
78
D
MÁ YFI 317 120-121
Jain Education International
For Private & Personal Use Only
www.jainelibrary.org
