Transition Metal Chemistry and Coordination Compounds Green/Damji – Chapter 3 Chang - Chapter 22 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

22.1 The Transition Metals

ScandiumTitaniumVanadium ChromiumManganeseIron CobaltNickelCopper 22.2

d-block Elements elements in which the d-subshell of an atom is being filled with electrons. have many similar chemical and physical properties dense, hard, metallic note electron configuration for Cr and Cu ? Why doesn’t the IE change much within the d-block as you move across period 4?

d-block Elements Look at the next slide… What patterns do you notice? in electron configuration? in electronegativity? in ionization energy? in size of radius?

22.1

Ionization Energies for the 1 st Row Transition Metals

22.1

Transition Metals – IB description elements having a partially filled d-sublevel in one of its common oxidation states share certain properties not shared with other metals (including Sc and Zn) ▪ variety of stable oxidation states ▪ ability to form complex ions ▪ formation of colored ions ▪ catalytic activity

Oxidation States of the 1 st Row Transition Metals (most stable oxidation numbers are shown in red) 22.1

Variety of Stable Oxidation States* of the 1 st Row Transition Metals (most stable oxidation numbers are shown in red) 22.1 *Oxidation state (aka oxidation number) is the charge an atom would have in a molecule if electrons were transferred completely. In the molecule CO 2, electrons are shared, but we say the oxidation state of carbon is 4 + and of each oxygen is 2 -.

Oxidation States of the 1 st Row Transition Metals 22.1 Notice Transition metals on the left have their maximum oxidation state as the most stable. This corresponds to the loss of all of the 3d and 4s electrons. [ 3+ for Sc 4+ for Ti ] These high oxidation states often occur in the oxyanion form. [ dichromate(VI) Cr 2 O 7 2- manganate(VII) MnO 4 - ] see p. 86 in Green and Damjii Transition metals on the right have the 2+ oxidation state as the most stable because the increasing nuclear charge actually increases the pull on the 3d electrons, making them less likely to be removed. [ 2+ for Co 2+ for Ni ]

Ability to form complex ions A complex ion contains a central metal cation bonded to one or more molecules or ions. The molecules or ions that surround the metal in a complex ion are called ligands. 22.3

Ability to form complex ions A ligand has at least one unshared pair of valence electrons – and may be a molecule or an ion H O H H N H H Cl - C N 22.3 The complex ion may be positively or negatively charged or may even be neutral if the charge of the central metal ion and ligands cancel one another.

Some sample complex ions from your lab Cu(NH 3 ) 4 2+ royal blue Zn(NH 3 ) 4 2+ colorless Ag(NH 3 ) 2 + colorless H N H H 22.3

How do I know how to write the formula for a complex ion? M n+ + xL m- = MLx (n-mx) where M is the metal; n is the charge of the metal L is the ligand; x is the number of ligands small m is the charge of the ligand (which could be 0) Ag tends to accept 2 electron pairs Cu tends to accept 4 electron pairs Other transition metals tend to accept 6 electron pairs

Extra credit opportunity: Locate a helpful resource that explains what goes on in transition metal complex ions to account for color. Explore the site and write notes – both on content and on it helpfulness to an IB student. Submit on or before test day. Transition metal ions

22.3

Coordination Compounds 22.3 The atom in a ligand that is bound directly to the metal atom is the donor atom. H O H H N H H The number of donor atoms surrounding the central metal atom in a complex ion is the coordination number. Ligands with: one donor atom monodentate two donor atoms bidentate three or more donor atoms polydentate H 2 O, NH 3, Cl - ethylenediamine EDTA A coordination compound typically consists of a complex ion and a counter ion.

Coordination Compounds 22.3 H 2 N CH 2 CH 2 NH 2 bidentate ligand polydentate ligand (EDTA) Bidentate and polydentate ligands are called chelating agents

Structure of Coordination Compounds 22.4 Coordination numberStructure Linear Tetrahedral or Square planar Octahedral

Structure of Coordination Compounds 22.4 Stereoisomers are compounds that are made up of the same types and numbers of atoms bonded together in the same sequence but with different spatial arrangements. Geometric isomers are stereoisomers that cannot be interconverted without breaking a chemical bond. cis-[Pt(NH 3 ) 2 Cl 2 ] trans-[Pt(NH 3 ) 2 Cl 2 ]

Structure of Coordination Compounds 22.4 cis-[Co(NH 3 ) 4 Cl 2 ]trans-[Co(NH 3 ) 4 Cl 2 ] Are these additional geometric isomers of [Co(NH 3 ) 4 Cl 2 ]? cis trans

Structure of Coordination Compounds 22.4 Optical isomers are nonsuperimposable mirror images. cis-[Co(en) 2 Cl 2 ]trans-[Co(en) 2 Cl 2 ] optical isomers chiral not optical isomers achiral

Structure of Coordination Compounds 22.4 Chiral molecules are optically active.

The formation of Colored Ions is due to the bonding in Coordination Compounds 22.5 All the d-orbitals are equal in energy in the absence of ligands!

Bonding in Coordination Compounds 22.5 Isolated transition metal atom Bonded transition metal atom When you add ligands, the energy levels of the d-orbitals are often impacted. Crystal field splitting (  ) is the energy difference between two sets of d orbitals in a metal atom when ligands are present The splitting shown is for an octahedral complex. The splitting is different for different shaped complexes.

Bonding in Coordination Compounds 22.5 When white light passes through a compound of a transition metal, a photon of energy is absorbed, and an electron is promoted to a higher energy level. The light that passes through the sample appears colored because some light has been absorbed. (The transmitted light is the complement of the absorbed light.) Ex. Cu(II) compounds absorb red and yellow light so that they look blue-green.

22.5 When white light passes through a compound of a transition metal, the light that passes through the sample appears colored because some light has been absorbed. (The transmitted light is the complement of the absorbed light.) Ex. Cu(II) compounds absorb red and yellow light so that they look blue-green.

Bonding in Coordination Compounds 22.5 I - < Br - < Cl - < OH - < F - < H 2 O < NH 3 < CN - < CO Spectrochemical Series Strong field ligands Large  Weak field ligands Small 

Catalytic Activity Transition metals and their ions are good catalysts because they… form complex ions with ligands (electron pair donors) [means the ligand and metal are close, as are the ligands to one another] have a wide variety of stable oxidation states, so they can readily gain and lose electrons

Heterogeneous Catalysis Surface of metal or metal compound serves as a place for the reaction to occur with a reduced activation energy MnO 2 Ex: 2 H 2 O 2 (aq)  2 H 2 O (l) + O 2 (g) Ni Ex: CH 2 CH 2 + H 2 (g)  CH 3 CH 3 (g) etheneethane

Heterogeneous Catalysis Catalytic converters in car exhaust systems Pd/Pt Ex: 2 CO (g) + 2 NO (g)  2 CO 2 (g) + N 2 (g) Haber Process Fe Ex: ______ (g) + ______ (g)  2 ______ (g) Contact Process V 2 O 5 Ex: ______ (g) + ______ (g)  2 ______ (g)

Homogeneous Catalysis Catalyst is in the same phase as the reactants Often involves a metal ion being oxidized in one stage (oxidation is the loss of electrons) and being reduced (reduction is the gain of electrons) in a second stage. Slow reaction: 2H 2 O 2 (aq) + H + (aq) + 2I - (aq)  2H 2 O (l) + I 2 (s) Catalyzed reaction: 2H 2 O 2 (aq) + H + (aq) + 2Fe 2+ (aq)  2H 2 O (l) + 2Fe 3+ (aq) followed by…. 2I - (aq) + 2Fe 3+ (aq)  I 2 (s) + 2Fe 2+ ( aq)