10.13. Other Transition Metals

10.13a. 4d block 2nd row of Transition Elements Y to Cd

• Yttrium, Y, Z=39, [Kr]4d¹5s², is not a true transition metal and is like scandium Z=21 forming the colourless Y³⁺_(aq) ion, e.c. = [Kr].

• Rhodium, Rh, Z=45, [Kr]4d¹⁰5s¹ : Metal used as catalyst in car exhaust (see platinum below for more details).

• Silver, Ag, Z=47, [Kr]4d¹⁰5s¹ 

  • Silver is a white lustrous metal that is soft, so very malleable and ductile. and has the highest electrical and thermal conductivity of any element of the periodic table.

  • Silver is used extensively in the electronics industry, jewellery, silverware and in alloys for use as coinage.

  • Silver is used as a catalyst in the chemical industry e.g. the production of alkene oxides.

  • Silver compounds are used in photography (AgCl, AgBr, AgI), antiseptics and for producing 'artificial' rain by seeding clouds with silver salts.

  • The silver(I) ion forms linear complexes with several ligands. The bond angle is 180^o and co–ordination number 2 e.g.

  • The water molecule ligands in the aqueous silver ion [Ag(H₂O)₂]⁺_(aq) can be replaced e.g. with (i) with ammonia, NH₃, (neutral ligand) giving a cationic complex, (ii) with the negative cyanide ion CN^– giving an anionic complex,  and (iii) the negative thiosulfate ion S₂O₃^2– forming an anionic complex:

    • [Ag(NH₃)₂]⁺_(aq) solution is used as Tollen's reagent (ammoniacal silver nitrate) in organic chemistry. It is readily reduced by aldehydes (NOT ketones) to form a 'silver mirror' on the side of the test tube on warming the mixture to 60^oC.

      • 2[Ag(NH₃)₂]⁺_(aq), + 2R–CHO_(aq) + 2OH^–_(aq) ==> 2Ag_(s) + 2RCOOH_(aq) + 4NH_3(aq)

      • redox:

    • [Ag(CN)₂]^–_(aq) solution is used in the electrolyte in silver electroplating. The object to be coated in silver is made the negative cathode electrode.

      • [Ag(H₂O)₂]⁺_(aq) + 2CN^–_(aq) [Ag(CN)₂]^–_(aq) + 2H₂O_(l)

      • The equilibrium is well over to the right but a very low concentration of silver ions gives a good even and strongly adhering surface deposit of silver metal on the conducting negative cathode electrode.

      • At the cathode (–): [Ag(H₂O)₂]⁺_(aq) + e^– ==> Ag_(s) + 2H₂O_(l)

      • The silver is replenished using a silver anode

      • At the anode (+): Ag_(s) + 2CN^–_(aq) – e^– ==> [Ag(CN)₂]^–_(aq)

    • [Ag(S₂O₃)₂]^3–_(aq) is formed when sodium thiosulphate is used to remove unreacted silver bromide (AgBr) or silver iodide (AgI) crystals in developing photographic films.

      • AgBr(s) + 2S₂O₃^2–_(aq) ==> [Ag(S₂O₃)₂]^3–_(aq) + Br^–_(aq)

      • NOT a redox reaction, Ag is +1 and Br is –1 throughout the reaction. The thiosulfate ion is here acting as a ligand and not a reducing agent e.g. like with iodine.

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  • The use of silver nitrate and ammonia for the halide test is described in the Chemical Tests Notes for anions

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10.13b. 5d block 3rd row elements La, Hf to Hg

• Platinum, Pt, Z=78, [Xe]5d⁹6s¹ 

  • Platinum is a bluish–white lustrous metal that is very malleable and ductile.

  • Platinum is relatively unreactive towards oxygen, water, and most acids, but it will dissolve in oxidising acids like nitric acid.

  • Platinum is used in the manufacture of jewellery because of its attractive appearance and anti–corrosion properties.

  • Platinum is used for thermocouples when alloyed with iridium Ir and Rhodium Rh.

  • Platinum is used for electrical contacts because of ite excellent electrical conductivity and resistance to corrosion.

  • Platinum and platinum compounds are used as catalysts in the chemical industry e.g. in the manufacture of ammonia, nitric acid, sulfuric acid and methanal.

  • Platinum has/is? been used as a catalyst, with rhodium, in catalytic converters of car exhausts to bring about reactions like

    • C_xH_{y (g)} + (x + ^y/₄)O_{2 (g)} ==> xCO_{2 (g)} + ^y/₂H₂O _(g) [to reduce unburned hydrocarbons]

    • 2CO _(g) + 2NO _(g) ==> N_{2 (g)} + 2CO_{2 (g)} [to reduce oxides of nitrogen and carbon monoxide emissions]

  • Platinum(II) complexes are used to prepare anti–cancer drugs used in chemotherapy.

    • The compound cis–diamminedichloroplatin(II), [Pt(NH₃)₂Cl₂]⁰, (known as cisplatin) is one of the most effective agents against cancers of the ovaries, bladder, and head and neck and helps as co–agent in the treatment of cancers of the cervix, lung and breast.

      • Its biggest success has been in the treatment of testicular cancer, a form of cancer previously resistant to any therapy but now considered to be curable in most cases.

      • However, cisplatin has three drawbacks which limit its usefulness:

        • (i) It is potentially very toxic,

        • (ii) it only affects a few particular types of tumors and it causes the development of resistance in the tumor cell.

      • The 'clinical point' however, is that you are balancing potentially harmful side effects against possible death.

    • The platinum stereochemistry is very important with the trans isomer showing no anti–cancer activity but the cis–isomer which is pharmacologically very active in its anti–carcinogenic activity (diagram below).

    • based on [Pt(NH₃)₂Cl₂]

    • cis/trans–platin are neutral, square planer complexes of co–ordination number 4, exhibiting geometrical isomerism. There of two of each of the monodentate ligands, chloride ion and ammonia and the blue lines/dots show the 4 dative covalent bonds.

    • The cis/trans isomerism is know called E/Z isomerism. In this case E = trans and Z = cis

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Scandium * Titanium * Vanadium * Chromium * Manganese * Iron * Cobalt * Nickel * Copper * Zinc * Silver & Platinum

keywords redox reactions ligand substitution displacement balanced equations formula complex ions complexes ligands colours oxidation states: silver ions Ag+ Ag(+1)  2 [Ag(NH3)2]+, + 2 R–CHO + 2 OH– ==> 2 Ag + 2 RCOOH + 4 NH3 [Ag(H2O)2]+ + 2 CN– [Ag(CN)2]– + 2 H2O AgBr + 2 S2O32– ==> [Ag(S2O3)2]3– + Br– platinum Pt(0) Pt2+ Pt(+2) [Pt(NH₃)₂Cl₂] oxidation states of silver platinum, redox reactions of silver platinum, ligand substitution displacement reactions of silver platinum, balanced equations of silver platinum chemistry, formula of silver platinum complex ions, shapes colours of silver platinum complexes

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Alphabetical Index for Science Pages Content A B C D E F G H I J K L M N O P Q R S T U V W X Y Z

Scandium * Titanium * Vanadium * Chromium * Manganese * Iron * Cobalt * Nickel * Copper * Zinc * Silver & Platinum

Introduction 3d–block Transition Metals * Appendix 1. Hydrated salts, acidity of hexa–aqua ions * Appendix 2. Complexes & ligands * Appendix 3. Complexes and isomerism * Appendix 4. Electron configuration & colour theory * Appendix 5. Redox equations, feasibility, E^ø * Appendix 6. Catalysis * Appendix 7. Redox equations * Appendix 8. Stability Constants and entropy changes * Appendix 9. Colorimetric analysis and complex ion formula * Appendix 10 3d block – extended data * Appendix 11 Some 3d–block compounds, complexes, oxidation states & electrode potentials * Appendix 12 Hydroxide complex precipitate 'pictures', formulae and equations