Presentation on theme: "Packing of more than one type of sphere into unit cells:"— Presentation transcript:
1 Packing of more than one type of sphere into unit cells: Packing of ions in saltsWhich is usually larger, negative (anions) or positive (cations) ions?Construct binary salts in lattice with anions usually occupying positions in unit cell and cations in holes in cellHow do you describe salts with more than one atom type? By unit cells and holesNaClSpace fill
2 Tetrahedron – 4 identical equilateral triangles 109.50Types of HolesIon in hole3 atoms e clouds in planeTETRAHEDRALWhat's a tetrahedronWhat's an octahedronHoles: Chemtube3DCubic close packed /Face-centred cubic (ccp/fcc)CCP and holesTetrahedron – 4 identical equilateral triangles5 atoms/ e clouds in planeSF6Octahedron – 8 identical trianglesOCT AHEDRALCUBICCube –
4 Example: NaCl (Jmol)xyzWhat type of unit cell is defined by the Cl- ions?z=1Top facez=0.5z=0Bottom faceTetrahedral HolesHow many tetrahedral holes are there in the fcc unit cell?Are there any Na+ ions occupying the holes?Octahedral HolesHow many octahedral holes are there in one fcc unit cell?In what type of holes are Na+ ions in edges throughout the whole lattice?
5 Hexagonal Closest Packing Z=1AArsenideNickelZ=0.75BZ=0.5Example: Nickel Arsenide (this Jmol link shows lattice based on Ni as in workbook pg 49, #4)Z=0.25In what type of hole is Ni found in the structure aboveHow many As are in the unit cell to the right? How many Ni?What is the formula for nickel arsenide?Locate a tetrahedral hole? Are there any Ni ions there?Z=0AUnit cell: hexagonal closest packingOf Arsenide with Ni in what holes?
6 Determining the empirical formula from unit cell data: A salt must be electrically neutral. If you know the charge on the cations and anions, you can determine MxNy.Alternatively, you can use crystal data to determine the structure of the unit cell and hence the empirical formula. Determine the number of each different ion in the following unit cells. Does it correspond to the formula from charge balance?Copper (I) chlorideCl4. Based on Cl- alone, what type of unit cell is this? What type of “hole” is occupied by Cu+?Cu2. Barium Chloride3. Rhenium oxideExamples from Chemtube3D