103 UNIT CELL GEOMETRY INTRODUCTION These cells are Most solids form crystal lattices composed of repeating box-like units (unit cells). These ce parallelepipeds whose shape is determined by the lengths of the edges of the parallelepipeds an between the edges. A cubic cell has 90° angles between all of its neighboring edges and all of its edge are equal to each other There are three possible arrangements of atoms within a cubic cell. In a simple cubic unit, there is an located at each corner of the cube (and each corner atom is shared by seven other ce atoms present in a simple cubic unit cell. Corner atoms touch each other (exce atom ere are no other pt in the diagonal direction) In a body-centered cubic unit, there are corner atoms (as in the simple cube), but, in addition atom completely within the body of the cube that is not shared with any other cell. In the body-centered eu cell, none of the corner atoms touch each other but they all touch the central atom bic In a face-centered cubic unit, there a there is an atom centered on each of the six faces of the cell. Half of a face-centered atom belongs to re, again, corner atoms shared with the surrounding cells. In addition, toms, The other half belongs to the cell adjacent to that face. Each face-centered atom touches its four corner a but the corner atoms do not touch each other PROCEDURE The class should divide into eight groups and each group will check out a cubic cell model kit. Each kit 1. should contain: 8-1/8 spheres; 6-1/2 spheres; 1 - whole sphere; metal connecting rods Consult the diagrams in your textbook and build a simple cubic unit cell. Collaborate with the seven other 2. 3. 4. 5. groups of students and assemble a model of a portion of a solid formed from eight simple cubic unit cells Draw a diagram of a simple cubic unit cell and answer the questions on the report sheet for this cell type Repeat steps 2 and 3 for the body-centered and face-centered cubic units Observe your profess or's demonstration of a hexagonal unit cell and answer the questions on the report sheet.