1. Silicon Silanes Silica, silicates, and zeolites Silicones Pure silicon
Computer chips

3. Silanes: SinH2n+2 Same structure as alkanes All unstable, pyrophoric: SiH4 + 2 O2  SiO2 + H2O Generally not stable beyond Si8 or so. No “silenes” because … __________________

4. Why would silanes be so much less stable than alkanes?
Bond Energies, kJ/mol:
C-C 346 C-H 413 C-O 358
Si-Si 222 Si-H 328 Si-O 452

5. Silica and Silicates Silica: SiO2 Si = +4 O = -2 Crystalline = quartz
Noncrystalline = vitreous

6. Silicates: Si-O anions + metal cations
General Rules:
Si always makes 4 Si-O bonds
Can be terminal (Si-O) or bridging (Si-O-Si)
Charge comes from Si = +4, O = -2

7. Structure depends on O/Si ratio SiO4 Predict Si2O7 Predict Si3O9

8. O/Si Ratio: 4
3.5 3

9. O/Si Ratio:
2.5
2.75 2

10. Silicates: General Trend As O/Si ratio decreases:

11. Tetrahedral structure depiction:

17. Aluminosilicates: Zeolites SiO2 base structure Substitute some Si atoms with Al

18. Another representation
Ball and stick Tetrahedral connectivity

19. Sodalite Cages

20. Formation of Zeolites from Sodalite Cages

21. Different arrangements
lead to different
pore spaces.

22. Charge and counter ions
Pure SiO2, 0% Al replacement
10% Al replacement

23. Affinity for water
Pure SiO2, 0% Al replacement
10% Al replacement

24. Zeolites and Catalysis
Purpose of a catalyst: increase rate, selectivity
Desired: react para isomer to form terephthalic acid
Problem: under reaction conditions, three isomers can interchange
So, might end up with wrong isomers of C6C4(CO2H)2

25. Solution
Catalyze reaction inside a zeolite pore that only accommodates the
para isomer.

26. Silicones

27. Synthesis of Silicone Precursors

28. General Reaction

29. Polydimethylsiloxane is the most common and available silicone.

30. Silicone Structure/Properties/Reactant Relationships