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Solid state X
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Packing of ions in ionic crystals

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.

U
Unacademy user
keep on sharing these tricks sir.... really it's helpful... enjoying the course 👌
Udit Gupta
10 months ago
Me too :)
Thank u so much ma'am for the lesson..... are these structures important for cbse boards
these are important for competitions
Thank u again ma'am
  1. XII 01 Solid State X


  2. Structure of NaCl Each Na is surrounded by six Cl ions at the coners of a regular octahedron and similarly each chlorie ion is surrounded by six Na ions. The co-ordination number of each is six and the arrgangements is called 6:6 = 0.524 r0.181 Cl ions have a cubic closed packed arrangement in which all octahedral holes are filled by Nat ions Most of the alkali metal halides (KCl, Nal, pbF, RbI), alkaline earth metal oxides and AgF, AgCl, AgBr, NHCI,NH4Br etc The unit cell of sodium chloride has four sodium ions and four chloride ions. Number of sodium ions # 12 (at the edge centre) X-+ 1 (at body centre) 4 Number of chloride ions 8(at the corners) x 6(at face centres) x4


  3. Na+


  4. Cs+ ion surrounded by 8 CI-ions The co-ordination number of each ions is eight. The radius ratio is 0.933 O Cs One unit cell


  5. Zinc Blend structure: (structu re It has ccp structure The ions are present at the corners of the cube and at the centre of each face. zinc ions occupy half of the tetrahedral sites. Each in ion is surrounded by four sulphide ions which are present towards the corners of a regular tetradedron. Each ion is surrounded by fou ions The structure is similar to diamond. zinc blende


  6. Wurtzite structure: It has hexagonal closed packed structure. S2-ions adopt hcp arrangement Zn2+ ions occupy half of tetrahedral sites Examples: ZnO, Agl. SiC etc O sa


  7. Structure of CaF, structure: (Fluorite structure Ca2+ ions are arranged in ccp arrangement. They are present at all the corners and at the centre of each face of the cube The fluoride ions occupy at all the tetrahedral sites This is 8:4 arrangement. i.e each Ca2+ ion is surrounded by 8F ions and each F ion is surrounded by four Ca2+ ions. o ca2+


  8. Structure of sodium oxide (Na20)Antifluorite structure: This structure is similar to CaF2 structure the difference being that in this structure the anion occupy the lattice sites and cations occupy the tetrahedral voids. Each Na ion is surrounded by fom 02 ions and each 02 ion is surrounded by eight Na ions Thus Na2O has 4:8 co-ordination structure


  9. Structure of oxides ofiron: Iron forms FeO, Fe203 and Fe 0 These oxides are interconvertible due to variable oxidation state and non stochiometry 1. Structure of FeO has a rock salt kind of structure Oxide ion (02-) forms f. .c packing and Fe2+ ions occupy all octahedral voids Normalspinel structure: MgAl204 is called spinel therefore its crystal structure is also called spinel. In this structure both tetrahedral and octahedral voids are simultaneously occupied. General formula in AB, 04 (A = divalent cations B = trivalent cations) Oxide ions form cubic closed packed arrangement Half of the octahedral voids are occupied by trivalent cations and one-eight of tetrahedral voids are occupied by divalent cations. Ferrites with general formula AFe204 have spinel type structure. They are used for making permanent andnon-rusting magnets.