question_answer

  Silver crystallises with face-centred cubic unit cell. Each side of this unit cell has a length of 409 pm. What is the radius of silver atom? Assume the atoms just touch each other on the diagonal across the face of the unit cell.                                                                                                                                                                                     [3] Or Aluminium crystallises in a cubic close packed structure. Radius of the atom in the metal is 125 pm. (i) What is the length of the side of the unit cell? (ii) How many unit cells are there in 1cm3 of aluminium?                                                                                [3]

Answer:

  Structure is fee a = length of each side = 409 pm                                                    [1] Radius = r For fee structure in which atoms just touch each other on the diagonal,                                                                                                                                                                      [1] Or (i) Radius =125 pm                     For cubic closed packed structure                                                                                                                                                                                                   (ii) Number of unit cells in 1 cm3                                                          unit cells