2. Elemental Se is trigonal, with long zig-zag chains arranged in helices about the c-axis. The helices can be either right-handed (space group P3421) or left-handed (space group P3221) as shown in the figure. There are three Se atoms in the unit cell (Z = 3). In right-handed Se, Left and right-handed forms of Se (on left and right the atoms are located in positions respectively) x,0,1/3; 0,x, 2/3; -x,-8,0 with x = 0.217. Atom locations in the left-handed enantiomorph are x,0,2/3; 0,x,1/3; again with x = 0.217. The coordinates are the same for tellurium, except that x = 0.269. For Se, the room temperature lattice parameters are a = 4.35517 and c = 4.94945 . For Te, the room temperature lattice parameters are a = 4.44698 and c = 5,91492 . a. Calculate the Se-Se and Te-Te bond lengths. b. What is the Se-Se-Se bond angle