In homework #2 you used Slater's rules to calculate Z* for Ru, Rh, Pd, Os, Ir, and Pt. Compare the trends in the first ionization potential, the electron affinity, the metallic radius, the Pauling electronegativity, and the density for these same six elements. Does Z*, as calculated by Slater's Rules, adequately explain the trends in each of these properties? Why or why not?
|
Element |
Z* |
IP (eV) |
EA (eV) |
rmetal (Å) |
Pauling Electronegativity |
Density (g/cm3) |
|
Ru |
3.25 |
7.361 |
1.05 |
1.34 |
2.2 |
12.41 |
|
Rh |
3.40 |
7.459 |
1.137 |
1.34 |
2.28 |
12.41 |
|
Pd |
6.85 |
8.337 |
0.562 |
1.37 |
2.20 |
12.02 |
|
Os |
3.75 |
8.438 |
1.1 |
1.35 |
2.2 |
22.57 |
|
Ir |
3.90 |
8.967 |
1.564 |
1.36 |
2.2 |
22.42 |
|
Pt |
3.55 |
8.959 |
2.128 |
1.39 |
2.2 |
21.45 |
Z* tracks with IP reasonably well, both across a period and between periods. In contrast, there appears to be little correlation between Z* and EA. The metallic radius and Pauling Electronegativity are essentially constant for all six of these metals, so Z* appears to have no influence. However, since n is larger for Os, Ir, and Pt, the radial function would expect one to expect a larger radius. This is not observed because of the poor shielding of the f electrons, which is a Z* effect. The densities in each period are close to constant and the difference between the two periods is solely based on mass.