Lecture #9, Friday, January 22nd

Coordination compounds contain a transition metal central atom with ligands coordinated to it through coordinate covalent bonds. Complex ions exist in solution as either positive or negative ions and form salts in the same manner as sodium chloride. Shown here is the crystal structure for NaCl and when we place it in water, it will dissolve into Na⁺ and Cl^- ions. Coordination complexes behave in the exact same manner, but the ions are typically much more complex.

For example, [Co(NH₃)₆]Cl₃ has a crystal structure shown here and dissolves into these ions in solution. It's the same principle, but things are a little more complicated. This forces us to come up with a system to identify and draw these complex ions in solution. Chemists use brackets to indicate the identity of the complex ion and outside the brackets is the counter ion. When you are asked for the coordination number of the transition metal cation you must only consider the ligands inside the brackets, but in order to determine the charge of the transition metal cation you must consider both the ligands inside the brackets and the counter ion.

I then discussed the early discoveries of Alfred Werner and showed how he came up with a reason for the different physical properties of various complexes by looking at the bonding at the transition metal center. He concluded that complexes can exist as isomers, or more specifically -cis and -trans.

We then showed how ligands bond to the transition metal centers through their lone pairs. In lab you will analyze various ligands and you are responsible for knowing the identity, charge, and which atoms in the ligand bind to the transition metal for the ligands listed in Table 24.2 on page 1019 of the text.

I also gave out the rules for naming transition metal complexes and worked through a few examples. You will need this information to complete the lab this week.

Songs played before class:
Bob Seger - Hollywood Nights
Rihanna ft. T.I. - Live Your Life lyrics