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Chemical Bonding – Giant Molecular Structures & their differences

Giant Molecular Structures

PropertiesDiamondGraphite
StructureAll carbon atoms connected to each other by very strong covalent bonds in a 3 dimensional structure.Each carbon atom is bonded to 4 other carbon atoms by very strong covalent bonds.

 

Also applicable to SiO2.

Flat layers of carbon atoms. Each carbon atom is connected to 3 other atoms by strong covalent bonds in a 2 dimensional hexagonal structure.
Electrical conductivity Diamond does not conduct electricity 

Each carbon atom uses up its 4 valence electrons for bonding with 4 other carbon atoms.

No free electrons to move and conduct elec.

Graphite can conduct electricity 

In each layer, a carbon atom is bonded to 3 other carbon atoms, leaving 1 valence electron free.

These electrons are delocalized, can travel along the layers, and conduct electricity.

 

Hardness or softnessGiant molecular structure held together by very strong covalent bonds. A lot of energy required to break all these bonds hence diamond is hard. Consist of layers of carbon atoms held together by very strong covalent bonds.Attractive forces between layers is weak, hence layers can slide past one another, making graphite soft.

 

Melting pointVery high melting point 

Structure

Giant molecular structure with millions of carbon atoms held together by very strong covalent bonds.

 

A large amount of energy is needed to break these bonds -> high m.p.

Very high melting point. 

Layers of carbon atoms held together by strong covalent bonds. A lot of energy needed to break these bonds -> high m.p.