Giant Molecular structure

Some substances consists of extremely large molecules or giant molecules. The molecules contains many hundreds and thousands of atoms covalently bonded with each other. We call this substances macromolecules.
E.g.: - Diamond, graphite, silicon (IV) oxide (silica)

Structure of Diamonds
• Each single crystal if a diamond is one giant molecule. carbon atom is bonded to other carbon atoms tetrahedrally.
• All the four outermost electrons in carbon atom are involved in the bond formation and there are no free electrons to move. therefore diamond does not conduct electricity.
• A lot if energy is required to break apart the strong covalent bonds between the carbon atoms, hence diamond has very high melting & boiling point.
• Diamond is the hardest substance known since the carbon atoms are not able to slide over each other due to strong covalent bonds.
• Diamond is a transparent, colourless crystal.

Structure of Graphite
• Graphite has a layered structure each carbon is bonded to three other carbon atoms in a hexagonal arrangement to form rings of regular hexagons. the different layers are held together by weak vanderwaal's force of attraction.
• Graphite has very high melting & boiling point. therefore a lot of energy is required to break apart the strong covalent bonds between the carbon atoms.
• It is a good conductor of electricity because each carbon atom uses only 3 out of 4 outer electrons for bonding with one free electron to conduct electricity.
• The weak vanderwaal's force between the layers enables layers to slide over each other. hence graphite is a soft substance.
• It is black, opaque and shiny solid.

Structure of Polythene
• Polythene is a plymer. It is made up of thousands of molecules called monomers joined together in long chains. The monomer used in making polythene is called ethene.
• Polythene has high melting point and does not conduct electricity.
• Polythene can be softened on heating and melting and set again when cooled.