1. Giant Covalent Compounds
Graphite and diamonds
Allotropes of carbon
Silicon and Quartz

2. Graphite Structure of Graphite
Carbon atoms are making covalent bonds in two directions. These carbon atoms are arranged in a hexagonal shape with alternating double bonds between the carbons.

3. Structure of graphite cont.
The hexagonal shapes form layers one on top of the other. Between the layers are Van der Waal forces which create a weak attraction between the layers.

4. Graphite’s structure

5. Electron microscope photo of a layer of graphite showing the hexagonal shapes.

6. 3-d graphite

7. Model showing multiple layers of graphite

8. Properties of graphite
It is a semiconductor. The alternating double bonds between the carbons conduct electricity.
It is very strong when compressed but weak when a shear force is applied.
Shear force causes the layers to slide along each other. This makes the graphite slippery and a good lubricant.

9. diamonds Structure of diamonds. Properties of diamonds
All of the carbons are covalently bonded to each other in a tetrahedral arrangement.
Properties of diamonds
They are strong in all directions. The tetrahedral arrangement makes a covalent bond in all dimensions.
They are not conductive.
Extremely high melting points.
Brittle.
High index of refraction. This “traps” light and makes them “sparkle”

10. Model of a diamond

11. 3-d structure of diamond

12. Photos of diamonds

15. Fullerenes Another allotrope of carbon
Most common is C60, but other forms have been discovered. C20 is the smallest fullerene to be discovered.
Shaped like a geodesic dome, C60 is made of 32 pentagons bonded together to make a ball shaped molecule.
Formed when graphite is vaporized in the presence of helium. Not found in nature.

16. Fullerenes continued Properties
Exist as discreet, individual molecules.
Nonpolar and dissolve in nonpolar organic solvents. (graphite and diamonds do not)
Can be reacted with metals at high temperatures.

17. Fullerenes

18. Silicon networks Pure silicon
Has the same tetrahedral arrangement as carbon
Larger radius reduces the bond strength between the atoms; they’re not as strong as a diamond

19. Silicon networks continued
Silicon dioxide, or silica
Empirical formula is SiO2 but it actually exists as SiO4 arranged in a tetrahedral arrangement where the Si atom is the center of a tetrahedral arrangement and the oxygen atoms are shared with other Si atoms.That is: each silicon is bonded to 4 oxygen atom, and each oxygen atom is bonded to two silicon atoms. Thus, SiO2
Forms sand and quartz crystal.
Melting silica (sand) above 1600 C turns it into glass, a disordered, amorphous solid.

20. Silica’s structure

22. Amorphous structure of glass

23. Summary of Carbon’s allotropes
Diamond
Graphite
fullerenes
Bonding arrangement
Bond strength
Physical properties

24. Carbon compared to silicon
Names of networks
Relative bond strength
Structure of their 3-d network