# A8 Superconducting Metals and X Ray Crystallography

1. i. Why do metals conduct electricity? ii. Explain why metals normally have electrical resistance. iii. Explain when and why metals can become superconductors which offer no electrical resistance. iv. What is the difference between Type 1 and Type 2 superconductors?
2. i. Explain the term unit cell as applied to a crystalline structure. ii. The first diagram is a body centred (BCC) unit cell. What is the total number of all atoms in this unit cell? iii. What is the coordination number of each atom in the first structure? Figure 11.4
iv. The second diagram shows a face centred unit (FCC) cell. What is the total number of atoms present in this unit cell? Figure 11.5
3. Using X rays of wavelength
$\textsf{1.45}\times\textsf{10}^\textsf{10}$
m on a crystal with a spacing between its atomic layers of
$\textsf{2.5}\times\textsf{10}^\textsf{10}$
. At what angle would you detect constructive interference?
4. If X rays of wavelength of
$\textsf{1.45}\times\textsf{10}^\textsf{10}$
m give constructive interference on a crystal at an angle of 15o, calculate the spacing between its atomic layers.
5. Potassium has a body-centred cubic lattice, atomic radius = 227pm. Silver has a face-centred cubic lattice, atomic radius = 144pm. i. Calculate the mass of an atom of: a. potassium b. silver ii. Calculate the mass of one unit cell of: a. potassium b. silver
6. For each of the following metals firstly calculate the length of the edge of the unit cell, then calculate the density of the metal. i. Copper which has a face centred cubic structure and an atomic radius of 135pm. ii. Tungsten which has a body centred cubic structure and an atomic radius of 135pm.