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Solid state III
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Ionic crystals and radius ratio

Shaillee Kaushal is teaching live on Unacademy Plus

Shaillee Kaushal
Faculty in Chemistry with a teaching experience of 14 years. Specialised in teaching for boards and competitions.

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  1. XII -01 Solid State Ill


  2. Crystallography: Branch of physical science which deals with the study of crystals i.e, their sources, classification, properties structure etc.


  3. lonic Crystals: Forces operating are purely electrostatic The lattice points are occupied by positively and negatively charged ions Each ion is surrounded by largest possible number of oppositely charged ions. This is called co-ordination number.


  4. NaCl Coordination number is six for both the ions. This means that eac sodium is surrounded by six chloride ions and each chloride is surrounded by six sodium ions CsCl = Co-ordination number for both is eight.


  5. Radius ratio PermittedGeometryExamples coordination number 0.155-0.225 3 0.225-0.4144 0.414- 0.732 6 0.732 1 Plane Triangular Tetrahedral Octahedral Cubic (bodycentred) 2. 3. 4. ZnS NaCl CsCl


  6. Space lattice and unit cell: The geometrical form consisting of a regular arrangement of points in space is called lattice or space lattice. It is a three dimensional network of constituent particles where they are placed in fixed positions. The smallest unit of the space lattice which explains the entire arrangement of the lattice in the unit cell. It is the repeating unit of the lattice Unit Cell Space Lattice Showing Unit Cell