o
o
o
o
Each metal atom donates one or more electrons to the group of mobile electrons which increases the electrical and thermal conductivity of the metallic elements.
Application of electric field makes these electrons flow through the linkage of positive ions.
Whereas application of heat to one portion of a metal makes the thermal energy spread uniformly throughout by free electrons.
Presence of free electrons in metals makes them lustrous, malleable and ductile. For example, Cr, Fe etc.
Covalent solids
o
Crystalline solids of non-metals comprises of covalent bonds between adjacent atoms that are strong and directional in nature due to which atoms are held very strongly at their positions all over the crystal.
Fig. Covalent bonding between Carbon and hydrogen o They are also called giant molecules. o These solids are very hard and brittle.
o
They have extremely high melting points and may decompose before melting.
o They are insulators and do not conduct electricity.
o
Diamond and silicon carbide are typical examples of such solids but Graphite is an exception as it is soft and a good conductor of electricity.