Presentation on theme: "Packing of more than one type of sphere into unit cells: -Packing of ions in salts -Which is usually larger, negative (anions) or positive (cations) ions?"— Presentation transcript:
Packing of more than one type of sphere into unit cells: -Packing of ions in salts -Which 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 cell NaCl Space fill How do you describe salts with more than one atom type? By unit cells and holes
3 atoms e clouds in plane TetrahedronTetrahedron – 4 identical equilateral triangles SF 6 5 atoms/ e clouds in plane OctahedronOctahedron – 8 identical triangles Types of Holes What's a tetrahedrontetrahedron What's an octahedronoctahedron Holes: Chemtube3D: Chemtube3D Cubic close packed / Face-centred cubic (ccp/fcc) CCP and holes Cube Cube – TETRAHEDRAL OCT AHEDRAL CUBIC Ion in hole
SIMPLE CUBIC PACKING HOLES C C CUBIC CUBIC CLOSEST PACKING – FACE CENTERED CUBIC HOLES T TT TT O O O tetrahedral octahedral Unit CellPacking EffCoord #Holes≈ Hole Size (r=1), Simple Cubic 0.526cubic Face centered Octahedral Tetrahedral O
Example: NaCl (Jmol)NaCl x y z z=0 z=0.5 z=1 Tetrahedral Holes How many tetrahedral holes are there in the fcc unit cell? Are there any Na + ions occupying the holes? Bottom face Top face Octahedral Holes How many octahedral holes are there in one fcc unit cell? In what type of holes are Na + ions in edges throughout the whole lattice? What type of unit cell is defined by the Cl - ions?
Example: Nickel Arsenide (this Jmol link shows lattice based on Ni as in workbook pg 49, #4 )Nickel Arsenide Unit cell: hexagonal closest packing Of Arsenide with Ni in what holes? Z=0 Z=0.25 Z=0.5 Z=0.75 A B Hexagonal Closest Packing In what type of hole is Ni found in the structure above How 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=1 A Arsenide Nickel
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 M x N y. 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? 1.Copper (I) chlorideCopper (I) chloride 2. Barium Chloride 3. Rhenium oxide 4. Based on Cl - alone, what type of unit cell is this? What type of “hole” is occupied by Cu + ? Cu Cl Examples from Chemtube3DChemtube3D