Problem Set 2 CH 3500: Inorganic Chemistry Plymouth State University Due: Monday, March 5, 11:15am No late work accepted!

Do not turn in this sheet of paper. All work and answers must be done on your own paper. For any problems requiring calculations, all work must be shown and must be readable to receive credit.

Nickeline, the mineral from which nickel was first obtained, has the chemical formula NiAs. The unit cell of this mineral is the prototype of an ionic structure that we did not study in class: the anions form a hexagonal close packed array, with the nickel cations filling in the octahedral holes (the true structure is distorted such that the octahedrons do not have ideal 90° angles). The following questions refer to the crystal structure of nickeline:

1. (4 pts) Sketch a 3-D representation of the nickeline unit cell, with appropriately labeled atoms. (tip: it is probably useful to use colored pens and draw the atoms as relatively small dots)

2. (6 pts) Provide a 2-D projection of the nickeline unit cell with the appropriate atomic coordinates.

3. (4 pts) Consult your drawings to determine the coordination numbers of nickel and arsenic in nickeline.

4. (2 pts) Look up and provide the electronegativities and ionic radii for nickel and arsenic. (Be sure to use the correct coordination number when looking up the radii; Table 1.4 as well as Resource Section 1 may be useful).

5. (6 pts) Indicate the position of nickeline on a Ketelaar triangle. Is nickeline a truely ionic compound? Explain your reasoning.

6. (4 pts) Determine the radius ratio (γ) for nickel and arsenic in nickeline. What coordination number does the radius ratio indicate for the two ions?

7. (4 pts) What coordination number is predicted for nickel and arsenic by the structure map (Pg 86, Fig 3.47 in your book)? Show your calculations and indicate your reasoning.

8. (6 pts) Use the Born-Mayer equation to determine the lattice enthalpy for nickeline.

9. (6 pts) Use the Kapustinski equation to determine the lattice enthalpy for nickeline.

10. (8 pts) A common semiconductor with arsenic anions is gallium arsenide (GaAs). Despite potential similarities to nickeline, gallium arsenide crystallizes in a rock salt structure. Look up the ionic radii of gallium and arsenic and use these to calculate the size of the unit cell in gallium arsenide.