CHEM 122 1st Edition Lecture 8Outline of Last LectureI. Solidsa. Crystallineb. AmorphousII. Structure of a CrystalIII. Cubic Unit Cellsa. Simple cubicb. Body-centered cubicc. Face-centered cubicIV. Packing Identical SpheresV. Number of particles per unit cellVI. Closest Packing of Identical SpheresOutline of Current Lecture I. Packinga. Hexagonalb. CcpII. Coordination Numbers of Cubic Unit CellsIII. Sodium Chloride Structure typeIV. CsCl Structure typeCurrent LectureThese notes represent a detailed interpretation of the professor’s lecture. GradeBuddy is best Used as a supplement to your own notes, not as a substitute.Packing:Hexagonal close-packed (hcp) structure: ABAB sequence where the A’s line up and the B’s line up. B is moved over one sphere from A giving it a staggered look.- Correspond to a hexagonal type unit cell- Coordination number of 12Cubic Close-packed (ccp) structure: ABCABC sequence where A’s line up, the B’s line up and the C’s line up. Each set is offset from one another.- Corresponds to a face-centered cubic unit cell- Coordination number 12Coordination Number of Cubic Unit Cells:Face-centered cubic: coordination number of 12, 74% of the volume is occupiedBody-centered cubic: coordination number of 8, 68% of the volume is occupiedPrimitive Cubic: coordination number of 6, 52% of volume is occupiedFace-centered cubic is the most efficient of the cubic unit cells (has the least empty space)Sodium Chloride structure:- Na has a radius of 95 pm and Cl has a radius of 181 pm. In ions, larger anions assume positions for either primitive cubic or fcc lattice. - Anions repel each other so cations are placed between them.- The unit cell is a fcc arrangement - In each unit cell there is 4 Cl ions and 4 Na ions, balancing the charges, which is required in a unit cell.- This structure is popular for ionic compounds that have the same charge.CsCl Structure:- In a primitive arrangement- Cs has a radius of 169 pm making Cl and Cs very close in size.- There is 1 Cs per unit cell and 1 Cl balancing the chargeWhy is there a difference in structure? It has to do with the size of the
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