The Demo Site

1) In first type of covalent bond molecules are small but bonded by weak forces.

*They have melting points and are soft
Eg;sulphur and iodine


2)In second type of covalent bond atoms are bonded by strong covalent bonds.

*They are very hard and having high melting points
Eg;diamond,germanium and silicon.


3)In third type of covalent bond within a layer all atoms are strongly bonded by covalent bonds perpendicular to the layer the materials are soft.
Eg;graphite
Other best examples of covalent solids; hydrogen peroxide, propylene, methane, 3rd,4th and 5th group elements form covalent solids.


Covalent bond characteristics.
1)multiple bonds have shorter bond lengths.
2)Double onds are shorter than single bond. This aspest is very important in polyners.
3)It is quantum mechanical phenomemon because spin is an intrinsic property in quantum mechanics.

Factors favouring the formation of covalent bond.
1)High ionisation energy.
2)equal electron affinity.
3)High molecular charge & small atomic size.

Properties of covalent solids.
1)covalent solids are crystalline in nature.
2)They are hard and brittle. But when compared to ionic solids not brittle.
3)Melting points & boiling points are high but low when compared to ionic crystals.
4)Few covalent solids are good insulators of electricity.
Eg;Diamond
*Hard and very high melting point
*Few covalent solids are semiconductors.
Eg;silicon, germanium
*Few covalent solids are good conductors of electricity
Eg;graytin
Property of graytin;soft and low melting point.
5)When covalent solids are doped with impurities they become semiconductors.
6)They are insoluble in water.
7)They are soluble in nonpolar solvents like benzene.
8)They are saturated.
9)They are highly directional i.e steriospecific.
10)As temperature increases conductivity increases in covalent solids.
11)Transparent to longer wavelengths.Opaque to shorter wavelengths.
Eg;
1)Diamond is transparent to wavelengths longer than u.v wavelengths.
2)ge and si is transparent to wavelengths longer than Ir wavelengths.
12)carbon in diamond structure is hard and melting point of diamond is 3280kelvin.
13)In hydrogen inter atomic seperation is 0.074mm and bond strength is 4.5ev.