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Published on January 4, 2008

Author: bruce

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Transition Metals & Coordination Chemistry:  Transition Metals & Coordination Chemistry Uses of Transition Metals Iron for steel Copper for wiring and pipes Titanium for paint Silver for photographic paper Platinum for catalysts Importance of Transition Metals:  Importance of Transition Metals U.S. imports 60 “strategic and critical” minerals Cobalt Manganese Platinum Palladium Chromium Important for economy and defense Transition Metals and Living Organisms:  Transition Metals and Living Organisms Iron – transport & storage of O2 Molybdenum and Iron Catalysts in nitrogen fixation Zinc – found in more than 150 biomolecules Copper and Iron – crucial role in respiratory cycle Cobalt – found in vitamin B12 Transition Metals: A survey:  Transition Metals: A survey Representative elements Chemistry changes across a period Similarities occur within a group Transition Metals Similarities occur within a period as well as within a group Due to last electrons being “d” (or “f”) orbital electrons Transition Metals: A Survey:  Transition Metals: A Survey “d” and “f” electrons cannot easily participate in bonding, so chemistry of transition elements are not affected by increased number of these electrons Transition Metal Behavior:  Transition Metal Behavior Typical metals Metallic Luster Relatively high electrical conductivity Relatively high thermal conductivity Silver is the best conductor of heat and electricity Copper is second best Properties of Transition Metals:  Properties of Transition Metals Transition metals vary considerably in some properties Melting point W – 3400oC vs. Hg, a liquid at 25oC Hardness Iron and Titanium are very hard Copper, gold, and silver are relatively soft Properties of Transition Metals:  Properties of Transition Metals Chemical Reactivity Reaction with oxygen Some form oxides that adhere to the metal, protecting the metal from further corrosion Cr, Ni, Co Some form oxides that scale off, resulting in exposure of the metal to further corrosion Fe Some noble metals do not form oxides readily Au, Ag, Pt, Pd Properties of Transition Metals:  Properties of Transition Metals Forming Ionic Compounds Transition Metals can form more than one oxidation state Fe+2 and Fe+3 Complex Ions Formed by the cations The transition metal ion is surrounded by a certain number of ligands (Lewis bases) Properties of Transition Metals:  Properties of Transition Metals In forming ionic compounds Most compounds are colored Transition metal ion can absorb visible light Most compounds are paramagnetic The transition metal ion contains unpaired electrons Electron Configurations:  Electron Configurations Energies of the 4s and 3d electrons are very similar Chromium is an exception to the diagonal rule, can be explained in terms of the similar energies of the 4s and 3d electrons 4s __ 3d __ __ __ __ __ Less electron-electron repulsion Electron Configurations:  Electron Configurations Transition metal ions Energy of the 3d orbital in transition metal ions is lower than the energy of the 4s orbital In other words, in forming a transition metal ion, the electrons are lost from the 4s orbital before the 3d orbitals. Mn: [Ar]4s23d5 Mn+2: [Ar]3d5 Oxidation States & I.E.:  Oxidation States & I.E. First five transition metals Maximum possible oxidation state is the result of losing the 4s and the 3d electrons Cr: [Ar]4s13d5; max. ox. state = +6 At the end of the period, +2 is the most common oxidation state. Too hard to remove the d electrons as they become lower in energy as the nuclear charge increases Standard Reduction Potentials:  Standard Reduction Potentials Metals act as reducing agents M  M+n + ne- Metal with the most positive reducing potential is the best reducing agent Sc  Sc+3 + 3 e- Eored = 2.08 V Ti  Ti+2 + 2e- Eored = 1.63 V All the metals except Cu can reduce H+ to H2 Reducing ability decreases going across the period 4d and 5d Transition Series:  4d and 5d Transition Series Radius increases in going from 3d to the 4d metals Radius of the 4d metals is similar to the 5d metals due to the lanthanide contraction Lanthanide Contraction:  Lanthanide Contraction Adding 4f electrons does not add to the size of the atom (as inner electrons) However, nuclear charge is still increasing. Increased nuclear charge offsets the normal increase in size in filling the next higher energy level Chemistry of 4d and 5d elements are very similar 4d and 5d transition metals:  4d and 5d transition metals Zr and ZrO2 – great resistance to high temperature, used for space vehicle parts exposed to high temperatures of reentry Niobium and Molybdenum – important alloying materials for steel Tantalum – resists attacks by body fluids, used for replacement of bones Platinum group: Ru, Os, Rh, Ir, Pd, Pt Used as catalysts Read:  Read Pg. 971 – 977 Look at pictures, note colors Coordination Compounds:  Coordination Compounds Coordination compound Formed by transition metal ions Usually colored Often paramagnetic Consists of A complex ion Made up of the transition metal ion with its attached ligands Counterions (the anions or cations needed to produce a neutral compound) Coordination Compounds:  Coordination Compounds [Co(NH3)5Cl]Cl2 Brackets hold the complex ion (Co(NH3)5Cl+2 The “Cl2” outside the brackets are the 2 Cl- counterions In solution: [Co(NH3)5Cl]Cl2 Co(NH3)5Cl+2 + 2 Cl- Coordination Compounds:  Coordination Compounds Alfred Werner in the 1890’s Transition metals have two types of valence (combining abilities) Primary valence – ability to form ionic bonds with oppositely charged ions Secondary valence – ability to to bind to Lewis bases (ligands) to form complex ions Coordination Compounds:  Coordination Compounds Primary Valence = Oxidation State Secondary Valence = Coordination Number number of bonds formed between the metal ion and the ligands in the complex ion. Coordination Number:  Coordination Number Coordination number Varies from two to eight Depends on the size, charge, and electron configuration of the transition metal Most common coordination number is 6 Next is 4, then 2 Many metals show more than one coordination number No way to predict which coordination number Coordination Compounds:  Coordination Compounds 6 ligands – octahedral geometry 4 ligands – square planar or tetrahedral geometry 2 ligands - linear Ligands:  Ligands Ligand Neutral molecule or ion having a lone electron pair that can be used to form a bond with a metal ion Metal-ligand bond Interaction between a Lewis acid and a Lewis base Also known as a coordinate covalent bond Ligands:  Ligands Unidentate (one tooth) ligand Can only form one bond with the metal ion H2O, CN-, NH3, NO2-, SCN-, OH-, Cl-, etc Bidentate ligand Can form two bonds to a metal Ethylenediamine, aka en, (H2N-CH2- CH2-NH2), oxalate Ligands:  Ligands Polydentate ligands (chelating ligands) EDTA, ethylenediaminetetraacetate Surrounds the metal Forms very stable complex ions with most metal ions Used as a scavenger to remove toxic heavy metals, e.g., lead, from the body Found in numerous consumer products to tie up trace metal ions Nomenclature:  Nomenclature Cation is named before the anion Ligands are named before the metal ion Naming ligands Add an o to the root name of an anion (fluoro, chloro, hydroxo, cyano, etc.) Neutral ligand, use the name of the molecule except for the following: H2O = aqua NH3 = ammine CH3NH2 = methylamine CO = carbonyl NO = nitro Nomenclature:  Nomenclature Use prefixes to indicate number of simple ligands (mono, di, tri, tetra, penta, hexa) Use bis, tris, tetrakis for complicated ligands that already contain di, tri, etc) Oxidation state of central metal ion is designated by a Roman numeral in parentheses When more than one type of ligand is present, they are named alphabetically, where prefixes do not affect the order. If the complex ion has a negative charge, add –ate to the name of the metal (eg. ferrate or cuprate) Nomenclature:  Nomenclature [Co(NH3)5Cl]Cl2 Pentaamminechlorocobalt(III) chloride K3Fe(CN)6 Potassium hexacyanoferrate(III) [Fe(en)2(NO2)2]2SO4 Bis(ethylenediamine)dinitroiron(III)sulfate Nomenclature:  Nomenclature Triamminebromoplatinum(II) chloride [Pt(NH3)3Br]Cl Potassium hexafluorocobaltate(III) K3[CoF6] The Crystal Field Model and Bonding in Complex Ions:  The Crystal Field Model and Bonding in Complex Ions Crystal field model focuses on the energies of the d orbitals Color and magnetism of complex ions are due to changes in the energies of the d orbitals caused by the metal-ligand interaction The Crystal Field Model:  The Crystal Field Model Crystal Field Model assumes Ligands are like negative point charges Metal-ligand bonding is entirely ionic In the free metal ion, all the d orbitals are degenerate, they have the same energies The Crystal Field Model:  The Crystal Field Model In the complex ion, the d orbitals are split into two sets with two different energies. Lower energy set The negative point charge ligands are farthest from the dxz, dyz, and dxy orbitals (the orbitals that point between the ligands) Electron pair repulsions are minimized The Crystal Field Model:  The Crystal Field Model In the complex ion, the d orbitals are split into two sets with two different energies. Higher energy set dz2, dx2-y2 point at the ligands More electron repulsions The Crystal Field Model:  The Crystal Field Model Splitting of the 3d orbital energies Results in the color and magnetism of the complex ions The Crystal Field Model:  The Crystal Field Model Strong field case (or low spin case) Splitting produced by the liqands is very large Electrons will pair in the lower energy orbitals (the ones pointing between the ligands) Result – a diamagnetic complex in which all electrons are paired The Crystal Field Model:  The Crystal Field Model Weak Field Case (or high spin case) Splitting produced by the ligands is very small Electrons will fill each of the five d orbitals (Hund’s rule) before pairing Will result in paramagnetism with unpaired electrons The Crystal Field Model:  The Crystal Field Model Ligands have different abilities to produce d-orbital splitting Strong Field ligands -----> Weak Field ligands Large D -------> Small D CN- > NO2- > en > NH3 > H2O > OH- > F-> Cl- > Br- > I- D increases as the charge on the metal ion increases Larger charge on ion pulls the ligands closer, results in greater splitting to minimize repulsions The Crystal Field Model and Colors:  The Crystal Field Model and Colors Colors of complex ions A complex ion will absorb certain wavelengths of light The color we see is complementary to the color absorbed. If yellow and green light is absorbed, then red and blue light passes through, so we would see violet. The Crystal Field Model and Colors:  The Crystal Field Model and Colors A complex ion will absorb a specific wavelength depending on the D between the d orbitals. Different ligands on the same metal ion will result in different colors because of the different D’s. DE = hc/l…for octahedral complex ions, the l is usually in the visible region Metallurgy:  Metallurgy Steps in the process of separating a metal from its ore (metallurgy) Mining Pretreatment of the ore Reduction to the free metal Purification of the metal (refining) Alloying Metallurgy:  Metallurgy Ores are mixtures containing Minerals (relatively pure metal compounds) Gangue (sand, clay, and rock) After mining, treat ores to remove the gangue and concentrate the mineral Pulverize and process ore Metallurgy:  Metallurgy Flotation process Allows minerals to float to the surface of a water-oil-detergent mixture Alter the mineral to prepare it for the reduction step Carbonates and hydroxides are heated CaCO3  CaO + CO2 Mg(OH)2  MgO + H2O Metallurgy:  Metallurgy Sulfides are converted to oxides by heating in air at temperatures below their melting points (roasting) 2 ZnS + 3 O2  2 ZnO + 2 SO2 Metallurgy:  Metallurgy Smelting – method used to reduce the metal ion to the free metal Depends on the affinity of the metal ion for electrons Good oxidizing agents produce the free metal in the roasting process HgS + O2  Hg(l) + SO2 Metallurgy:  Metallurgy More active metals Use coke (impure carbon), carbon monoxide, or hydrogen, as a strong reducing agent Fe2O3 + 3 CO  2 Fe + 3 CO2 WO3 + 3 H2  W(l) + 3 H2O ZnO + C  Zn(l) + CO Metallurgy:  Metallurgy Most active metals (Al and alkali metals) must be reduced electrolytically from the molten salts. Metallurgy of Iron:  Metallurgy of Iron Iron ores pyrite (FeS2), siderite (FeCO3), hematite(Fe2O3, magnetite (Fe3O4) Concentrate iron in iron ores Separate Fe3O4 mineral from the gangue by magnets Iron ores that are not magnetic are converted to Fe3O4, or are concentrated using the flotation process Metallurgy of Iron:  Metallurgy of Iron Reduction process Occurs in the blast furnace Uses coke which is converted to CO in the blast furnace Reduction occurs in steps: 3Fe2O3 + CO  2 Fe3O4 + CO2 Fe3O4 + CO  3 FeO + CO2 FeO + CO  Fe + CO2 Metallurgy of Iron:  Metallurgy of Iron The iron can reduce the CO2: Fe + CO2  FeO + CO So the excess CO2 needs to be removed by adding excess coke: CO2 + C  2 CO

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