1. Giant Molecular Structures (Or giant covalent structures)

2. Allotropes: different forms of the same element.
Carbon has several allotropes – the best known being diamond and graphite

3. Structure of part of a diamond molecule

4. Contains only carbon atoms
3 dimensional tetrahedral structure
Strong covalent bonds
Strong substance
High melting point and boiling point
MP 3550℃
All the valence electrons are used in bonding, so diamond doesn’t conduct

5. Graphite

6. Graphite is another allotrope of carbon
Contains a 2 dimensional giant covalent structure
Each layer is strong, but there are only weak forces between layers.
Layers can slide over each other, hence graphite is used as a lubricant and in pencils.
Each carbon only makes 3 bond
The remaining delocalised electrons are free to move, hence graphite is a conductor.
Similar mp to diamond (? – you could research this. There is some contradictory evidence around)

7. Fullerene C60

8. The fullerenes are actually a whole chemical family.
They are allotropes of carbon.
They are spherical molecules consisting of 5 and 6 membered rings of carbon atoms.
C60 is the one which has been studied most.

9. Each carbon is bonded to 3 other atoms, so there are delocalised electrons.
However, because the surface isn’t flat the electrons cannot easily flow from one molecule to another.
C60 has a conductivity greater than diamond, but MUCH less than graphite.
Unusually, C60 is soluble in non polar solvents
It has a lower MP than diamond or graphite (800K)

10. Nanotubes

11. Nanotubes are another allotrope of carbon.
They are “state of the art” technology
We will study them more in the option “Chemistry in Industry and Technology”

12. Silicon compounds Silicon is in the same group as carbon
So the structure of silicon is very similar to that of diamond.
The larger atoms means that the covalent bonding is not as strong
So silicon is weaker than diamond and has a lower MP and BP.
MP 1414 °C
Silicon doesn’t have any allotropes like graphite or fullerenes.

13. Silicon dioxide also has a similar structure to diamond.

14. Silicon dioxide

15. It is giant molecular
It has a tetrahedral structure
Each silicon atom is bonded to 4 oxygen atoms
Each oxygen atom is bonded to 2 silicon atoms