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CHEM 163 Chapter 23

CHEM 163 Chapter 23. Spring 2009. http://www.youtube.com/watch?v=kfgtU9DDvdY. Transition Metals. Large part of inorganic chemistry. Electron Configurations. [Ar]4s 2 3d 10. Mn :. [Ar]4s 2 3d 5. Zn:. General form:. [noble gas] ns 2 (n-1)d x. n= 4 or 5. x = 1 to 10.

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CHEM 163 Chapter 23

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  1. CHEM 163Chapter 23 Spring 2009 http://www.youtube.com/watch?v=kfgtU9DDvdY

  2. Transition Metals • Large part of inorganic chemistry

  3. Electron Configurations [Ar]4s23d10 Mn: [Ar]4s23d5 Zn: General form: [noble gas] ns2 (n-1)dx n= 4 or 5 x = 1 to 10 [noble gas] ns2 (n-2)f14 (n-1)dx n= 6, or 7 x = 1 to 10 Cr: [Ar]4s13d5 Cu: [Ar]4s13d10

  4. Transition Elements: Periodic Trends Across a period: • Atomic size: decreases, then remains constant • d e- are filling inner orbitals • Shield outer e- from nuclear pull • Electronegativity: increases slightly • Ionization Energy: increases slightly • d e- shield nuclear pull effectively

  5. Transition Elements: Periodic Trends Within a group: • Atomic size: no change • Increase in size between periods • Increase in nuclear charge (32!)  decreased size • Electronegativity: increases slightly • More electronegative than elements in lower periods (increasing nuclear charge) • Ionization Energy: increases • Small increase in size; large increase in nuclear charge Density • Across a period: increase, then level off • Down a group: increase dramatically • Size constant

  6. Chemical Properties • Multiple oxidation states • Electrons close in E (all ready for bonding) • Highest oxidation state = group number for 3B(3) to 7B(7) • +2 oxidation state is common • Metallic behavior • Lower oxidation state – ionic bonding • Higher oxidation state – covalent bonding • Reducing strength • All period 4 TMs form H2 from acid (except Cu) s electrons!

  7. Color! • To absorb visible light, e- need a nearby higher E level • Main group ionic compounds have full outer shells • Next E level far away • Only colorless TM compounds include: • Sc3+, Ti4+, Zn2+ compounds of period 4 transition metals

  8. Magnetic Properties • Paramagnetic: unpaired electrons • Diamagnetic: all e- paired Attracted to an external magnetic field Unaffected by an external magnetic field • Most main-group metal ions have full shells • Compounds with TM ions typically have unpaired e- • Compounds with TM ions with d0 or d10 are diamagnetic

  9. Inner Transition Elements • Lanthanides • “rare earth elements” • Not actually rare • 14 elements • Cerium (Z = 58) through Lutetium (Z = 71) • Silvery, high-melting (800-1600 °C) • Applications: • Tinted sunglasses • strongest known permanent magnet (SmCo5) • catalysts • Actinides • Radioactive! • Some never been seen/only made in labs "Lanthanum has only one important oxidation state in aqueous solution, the +3 state. With few exceptions, that statement tells the whole boring story about the other fourteen elements" - Pimental & Spratley (1971 textbook)

  10. Chromium • Protective coating of Cr2O3 forms in air • Exists in several oxidation states • CrO4 2- : yellow • Cr2O72- : orange • CrO3 : deep red • Cr3+ : blue/violet • Cr(OH)4- : green • Cr (s) and Cr2+ : strong reducing agents • Cr6+ in acid: strong oxidizing agent

  11. Manganese • Used in steel alloys • more easy to work • tougher • Several oxidation states • Mn with oxidation states > +2 are good oxidizing agents • Does not easily oxidize in air • Already stable with d5 configuration

  12. Mercury • Forms bonds that can be ionic or more covalent • Can be found in the +1 oxidation state • [Xe] 6s1 4f14 5d10 http://www.youtube.com/watch?v=oL0M_6bfzkU

  13. Silver • Soft • Sterling silver is alloyed with Cu to harden • Highest electrical conductivity of any element • 63.01 × 106 S/m • O.N. = +1 • Doesn’t form oxides in air • Tarnishes into Ag2S (Cu: 59.6 × 106 S/m) Strong reducing agent

  14. Black and White Photography Film: plastic coated in gelatin containing AgBr microcrystals

  15. Coordination Compounds TM form coordination compounds or complexes • Complex ion • central metal cation • ligands (Anions or molecules with lone pairs) • Counter ions • maintain charge neutrality Coordination compounds dissociate in water

  16. Complex Ions • Coordination Number: • # of ligand atoms bonded directly to the TM ion • Most common C.N. = 6 • Geometry: • C.N. = 2 • C.N. = 4 • C.N. = 6 linear square planar tetrahedral octahedral

  17. Ligands • Contain donor atoms • form covalent bond with metal (donates e- pair) • Monodentate: • Bidentate: • Tridentate: 1 donor atom 2 donor atoms 3 donor atoms

  18. Coordination Compound Formulas • Cation written before anion • Neutral ligands written before anionic ligands • Whole ion written in brackets • may be cationic or anionic • Charge of cation(s) balanced by charge of anion(s) Tetraaminebromochloroplatinum(IV) chloride [cation] Cl- 2+ Need 2Cl- [Pt(NH3)4BrCl] [Pt(NH3)4BrCl]Cl2 Potassium amminepentachloroplatinate (IV) K[Pt(NH3)Cl5]

  19. Naming Coordination Compounds • Name cation first, then anion • Within the complex ion, ligands named (in alphabetical order) before TM • Ligands • most molecules names stay same • anions lose –ide; add –o • Prefix tells how many • If ligand name already contains prefix, use: bis (2); tris (3); tetrakis (4) • TM oxidation state in parentheses (if multiple possible) • If complex ion is an anion, change to –ate K[Pt(NH3)Cl5]

  20. Isomers Compounds with same chemical formula, different properties • Constitutional Isomers: • Same atoms connected differently • [MA5B]B2 and [MA3B3]A2 • Linkage Isomers: • Same atoms, same complex ion, ligand connected differently • Nitrite ligand: NO2-

  21. Geometric Isomers • Same ligands, arranged differently around TM • cis- and trans-

  22. Optical Isomers • Physically identical except rotate polarized light differently • “enantiomers” (like hands)

  23. Bonding in Complexes • Coordinate covalent bond: • Both electrons from one atom • Complex ion is a Lewis adduct • Ligand: Lewis base • Metal: Lewis acid • Crystal Field theory • Describes d-orbital energies (TM) as ligands approach

  24. d orbitals dxz dyz dz2 dx2 - y2 • In an atom- all d orbitals have same E • When part of coordination compound, E changes happen dxy Crystal Field Splitting eg dz2 dx2 - y2 E ∆E dxy dxz dyz t2g • Large ∆E: strong field ligand • Small ∆E: weak field ligand

  25. Splitting of d orbitals • Minimized energy when ligands approach TM on axes • dxy dyz dxz lie between approaching ligands – minimal repulsion

  26. d orbital splitting dx2 - y2 dxy dz2 dx2 - y2 dxy dxz dyz E dz2 dz2 dx2 - y2 dxz dyz dxy dxz dyz Square Planar Octahedral Tetrahedral

  27. Color of TM • We see reflected/transmitted colors • Absorbed complementary color • For a given ligand, color depends on TM oxidation state • For a given metal, color depends on ligand field strength

  28. Magnetic Properties of TM Mn2+: d5 [Mn(H2O)6]2+ [Mn(CN)6]4- Mn2+: d5 E Weak-field ligand Strong-field ligand High spin Low spin

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