Humboldt State University ® Department of Chemistry

Richard A. Paselk

Chem 110	General Chemistry	Fall 2003
Lecture Notes::Lec 33_19 November	© R. Paselk 2003
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The Chemistry of the Elements

The Transition Metals

Last time we looked at some of the physical properties of the Transition metals and their wide variations. We also noted some of the chemical similarities they share. Continuing this discussion of chemical properties, we see:

• The transition elements tend to have multiple oxidation states.
  • First and last elements of series have one oxidation state:
    • First elements (Sc, Y, Lu) = +3 only, corresponding to the removal of the s-electrons and the single d-electron.
    • Last elements (Zn, Cd, Hg) = +2 (but Hg also has a +1 state for the bound Hg-Hg⁺² ion).
  • The oxidation states tend to increase in number and value towards the center of the series (see table below):
    • In the first half of each series the maximum oxidation state corresponds to the loss of the s-electrons and all of the d-electrons (with ruthenium and osmium the maximum goes to +8).
    • In the second half of the series the decreasing oxidation maximum oxidation numbers result from the increased stability of the half-filled d subshell.

Periodic Table of the Elements -Transition Metals IIIB IVB VB VI VIIB VIIIB IB IIB 21Sc 4s23d1 E°=-2.08V*   3** 22Ti 4s23d2 E°=-1.63V (2) 3 23V 4s23d3 E°=-1.2V 2 3 4 5 24Cr 4s13d5 E°=-0.74V 2 3 (4)   6 25Mn 4s23d5 E°=-1.18V 2 (3) 4   (6) 7 26Fe 4s23d6 E°=-0.45V 2 3 (4)   (6) 27Co 4s23d7 E°=-0.28V 2 3 28Ni 4s23d8 E°=-0.26V 2 (3) 29Cu 4s13d10 E°=+0.34V (1), 2 30Zn 4s23d10 E°=-0.76V 2  Y Zr Nb Mo 5s14d5 Tc   E°=+0.4V Ru   E°=+0.5V Rh   E°=+0.6V Pd 5s04d10 E°=+1.2V  Ag 5s14d10 E°=+0.80V  Cd Lu  Hf Ta  W 6s24d4 Re Os   E°=+0.9V Ir   E°=+1.0V  Pt 6s14d9 E°=+1.2V Au 6s14d10 E°=+1.7V  Hg   E°=+0.80V * Reduction potentials from M+2 (or M+3 for Sc & Cr) to the metal. ** Common oxidation states (less common in parenthesis).

• The reactivities of the transition metals varies significantly for both chemical and physical reasons, e.g.:
  • Fe oxidizes readily and continuously because the oxides formed flake off yielding fresh metal to continue reacting.
  • Cr and Ni readily form oxides, but they tend to form a continuous and impervious layer which protects the metal from additional corrosion.
  • Au, Ag, and Pt do not readily form oxides.

Coordination Compounds

Complex ions are particularly common in the transition metals. When a complex ion is combined with a counter ion the result is a coordination compound. Note that complex ions can be both cations and anions, and a compound could be made up from two different complex ions.

When dealing with complex ions and coordination compounds one of the first things we need to be concerned with is nomenclature - how do we know what someone is talking about, and how do we describe a compound of interest?

Nomenclature of Complex Ions: Note that we still write, in formulae and names, the cation first and the anion second. The question then is how do we name the components of the complex ions themselves:

• Ligand Naming: Since complex ions are made up of a central metal atom and the ligands surrounding it, the first thing we need is a way of designating the ligands.
  • Anionic Ligands have names which are modified from the standard names:
    • If the anion name ends in -ide the ligand name ends in -o instead:

Anion Name Ligand Name Cl- chloride -Cl chloro I- iodide -I iodo CN- cyanide -CN cyano OH- hydroxide -OH hydroxo

• If the anion name ends in -ate then the ligand name ends in -ato instead:

Anion Name Ligand Name SO42- sulfate -OSO3 sulfato C2O42- oxalate -O(CO)2O- oxalato

• Some anions may bind to a central atom in more than one way, so different names are used for the different arrangements. Two important examples are given below:

Anion Name Ligand Name SCN- thiocyanate -SCN thiocyanato     -NCS isothiocyanato NO2- nitrite -NO2 nitro     -ONO nitrito

• Molecular (neutral) and cationic ligands are generally not renamed when used as ligands. The three most important exceptions to this rule are listed below:

Molecule Name Ligand Name H2O water -OH2 aqua (old = aquo) NH3 ammonia -NH3 amine CO carbon monoxide -CO carbonyl

• Complex Ion Naming:
  1. The ligands in a complex ion are named first, even though they are listed after the cation in the formula.
  2. The number of each ligand is indicated using Greek prefixes (di- = 2, tri- = 3, tetra- = 4, penta- = 5, and hexa- = 6).
  3. When there is more than one kind of ligand, they are listed alphabetically by ligand name (prefixes like tetra- and bis- are ignored in the ordering).
  4. The oxidation number of the central atom is indicated with a Roman numeral as in the Stock System for naming cations, e.g. iron(III).
  5. Complex anions have the suffix -ate added to the name of the central atom. Note that some atoms use their Latin names, e.g. cuprate vs. nickelate

Examples

Formula Name [Cr(H2O)6]3+ Hexaaquachromium(III) ion [CoCl4(NH3)2]- Diamminetetrachlorocobaltate(III) ion

© R A Paselk

Last modified 14 December 2003