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ChemistryMediumClass 11

Silicon — SiO₂, silicates, silicones

p-block Elements (Class 11 — Groups 13 & 14)

10

JEE Qs

8%

Hard

60

min

Focus on understanding the structural diversity of silicates based on oxygen sharing and the synthesis pathway and properties of silicones, particularly the role of starting materials.

🧮 Key Formulas

SiO4^4- (basic orthosilicate unit)
Si2O7^6- (pyrosilicate unit)
(SiO3^2-)_n (cyclic and single chain silicates)
(Si4O11^6-)_n (double chain/amphibole silicates)
(Si2O5^2-)_n (sheet silicates)
(SiO2)_n (3D network silicates, e.g., quartz)
RCl + Si (Cu, 573K) --> R2SiCl2 (major product, precursor for silicones)
R2SiCl2 + 2H2O --> R2Si(OH)2 + 2HCl (hydrolysis)
n R2Si(OH)2 --> (-R2SiO-)_n + n H2O (condensation polymerization to form silicones)

✅ Key Points for JEE

  • 1Silicon dioxide (SiO2) exists as a 3D network solid where each silicon atom is tetrahedrally bonded to four oxygen atoms, and each oxygen atom is bonded to two silicon atoms, resulting in a giant covalent structure.
  • 2Silicates are classified based on how the basic SiO4^4- tetrahedral units are linked together by sharing oxygen atoms, leading to structures like ortho-, pyro-, cyclic, chain, sheet, and 3D silicates.
  • 3Silicones are organosilicon polymers containing R2SiO repeating units, known for their hydrophobic nature, high thermal stability, chemical inertness, and low toxicity.
  • 4The preparation of silicones involves the hydrolysis of alkyl/aryl substituted chlorosilanes (R2SiCl2), followed by a condensation polymerization reaction to form linear, cyclic, or cross-linked polymers. Chain length control is achieved by adding R3SiCl.

⚠️ Common Mistakes

  • ✕Confusing the structural differences and properties between silicates (inorganic mineral compounds) and silicones (synthetic organosilicon polymers).
  • ✕Incorrectly identifying the basic building block of silicates as an SiO2 molecule rather than the tetrahedral SiO4^4- unit.
  • ✕Not understanding the role of different chlorosilanes (RSiCl3, R2SiCl2, R3SiCl) in determining the degree of cross-linking and termination of silicone chains.

NCERT Chapters

  • Class 11 Chemistry Ch 11: The p-Block Elements