Silicon Silanes Silica silicates and zeolites Silicones Pure

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

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

Silanes: Sin. H 2 n+2 Same structure as alkanes All unstable, pyrophoric: Si. H

Silanes: Sin. H 2 n+2 Same structure as alkanes All unstable, pyrophoric: Si. H 4 + 2 O 2 Si. O 2 + H 2 O Generally not stable beyond Si 8 or so. No “silenes” because … _________

Why would silanes be so much less stable than alkanes? Bond Energies, k. J/mol:

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

Silica and Silicates Silica: Si. O 2 Si = +4 O = -2 Crystalline

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

Silicates: Si-O anions + metal cations General Rules: 1. Si always makes 4 Si-O

Silicates: Si-O anions + metal cations General Rules: 1. Si always makes 4 Si-O bonds 2. O can be terminal (Si-O) or bridging (Si-O-Si) 3. Charge comes from Si = +4, O = -2

Structure depends on O/Si ratio Si. O 4 Predict Si 2 O 7 Predict

Structure depends on O/Si ratio Si. O 4 Predict Si 2 O 7 Predict Si 3 O 9

O/Si Ratio: 4 3. 5 3

O/Si Ratio: 4 3. 5 3

O/Si Ratio: 2. 5 2. 75 2

O/Si Ratio: 2. 5 2. 75 2

Silicates: General Trend As O/Si ratio decreases:

Silicates: General Trend As O/Si ratio decreases:

Tetrahedral structure depiction:

Tetrahedral structure depiction:

Aluminosilicates: Zeolites Si. O 2 base structure Substitute some Si atoms with Al

Aluminosilicates: Zeolites Si. O 2 base structure Substitute some Si atoms with Al

Another representation Ball and stick Tetrahedral connectivity

Another representation Ball and stick Tetrahedral connectivity

Sodalite Cages

Sodalite Cages

Formation of Zeolites from Sodalite Cages

Formation of Zeolites from Sodalite Cages

Different arrangements lead to different pore spaces.

Different arrangements lead to different pore spaces.

Charge and counter ions Pure Si. O 2, 0% Al replacement 10% Al replacement

Charge and counter ions Pure Si. O 2, 0% Al replacement 10% Al replacement

Affinity for water Pure Si. O 2, 0% Al replacement 10% Al replacement

Affinity for water Pure Si. O 2, 0% Al replacement 10% Al replacement

Zeolites and Catalysis Purpose of a catalyst: increase rate, selectivity Desired: react para isomer

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 C 6 C 4(CO 2 H)2

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

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

Silicones

Silicones

Synthesis of Silicone Precursors

Synthesis of Silicone Precursors

General Reaction

General Reaction

Polydimethylsiloxane is the most common and available silicone.

Polydimethylsiloxane is the most common and available silicone.

Silicone Structure/Properties/Reactant Relationships

Silicone Structure/Properties/Reactant Relationships

Silicone Structure/Properties/Reactant Relationships

Silicone Structure/Properties/Reactant Relationships