Silicon

1
Silicon

• Silanes
• Silica, silicates, and zeolites
• Silicones
• Pure silicon
• Computer chips

2
(No Transcript)
3
Silanes SinH2n2Same structure as alkanesAll
unstable, pyrophoric SiH4 2 O2 ? SiO2
H2OGenerally 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
• O can be terminal (Si-O) or bridging (Si-O-Si)
• Charge comes from Si 4, O -2

7
Structure depends on O/Si ratioSiO4Predict
Si2O7Predict Si3O9
8
O/Si Ratio 4 3.5 3
9
O/Si Ratio 2.5 2.75 2
10
Silicates General TrendAs O/Si ratio
decreases
11
Tetrahedral structure depiction
12
(No Transcript)
13
(No Transcript)
14
(No Transcript)
15
(No Transcript)
16
(No Transcript)
17
Aluminosilicates ZeolitesSiO2 base
structureSubstitute 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
10 Al replacement
Pure SiO2, 0 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