1.Strontium forms face-centered cubic crystals. The atomicradius of a strontium
ID: 685067 • Letter: 1
Question
1.Strontium forms face-centered cubic crystals. The atomicradius of a strontium atom is 215 pm. Consider the face of a unitcell with the nuclei of the strontium atoms at the lattice points.The atoms are in contact along the diagonal. Calculate the lengthof an edge of this unit cell.______________pm 2.How many atoms are contained in one unit cell of metallictungsten if it forms a face centered cubic unit cell? 3. A unit cell of sodium chloride (face centered cubic) waschosen so that the face-centered cube was formed from sodium ions.A certain number of sodium ion lattice points and a certain numberof chloride ion lattice points are required. How many chloride ionlattice points are in the unit cell as described above 1.Strontium forms face-centered cubic crystals. The atomicradius of a strontium atom is 215 pm. Consider the face of a unitcell with the nuclei of the strontium atoms at the lattice points.The atoms are in contact along the diagonal. Calculate the lengthof an edge of this unit cell.
______________pm 2.How many atoms are contained in one unit cell of metallictungsten if it forms a face centered cubic unit cell? 3. A unit cell of sodium chloride (face centered cubic) waschosen so that the face-centered cube was formed from sodium ions.A certain number of sodium ion lattice points and a certain numberof chloride ion lattice points are required. How many chloride ionlattice points are in the unit cell as described above
Explanation / Answer
If a nucleus and two atom are at the lattice points, a facediagonal has a distance of 2r (from nucleus) + 1r (first atom atthe first lattice point) + 1r (second atom at the second latticepoint) = 4r The edge of the unit cell =s s2 = face diagonal = 4r s = (4/2)*r = (4/2)*215 pm = 608 pm 2) 6 faces, 0.5 atoms at the center of each face => 3atoms 8 vertices, 1/8 atom at each vertex => 8*(1/8) = 1atom total o f4 atoms 3) Like in 2), there are 4 Na per unit cell. To counteract the 4+charge of 4 Na+ ions, there must be 4 Cl-
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