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Indian Forest Service (Mains)

Chemistry optional

  • 2 papers
  • 200 marks each
  • 3 h per paper

Paper I covers physical and inorganic chemistry.

Indian Forest Service (Mains), Chemistry optional · 2022 · Paper I

Q2(c)(ii). Why zinc blende is face-centred cubic

Question

Zinc blende lattice is face-centered cubic. However, each atom is tetrahedrally bonded to four nearest neighbours. Explain how zinc blende lattice can be a face-centered cubic lattice.

Answer in brief

Face-centred cubic describes the translational Bravais lattice; tetrahedral describes the local Zn–S coordination. They refer to different features.

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Topic notes: crystal systems, Bragg's law, X-ray diffraction and radius ratio, with every Civil Services, IFoS and Geo-Scientist PYQ →

Coverszinc blendeFCC latticelattice and basisBravais latticetetrahedral voidsZnS structure

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