Transition Metal Chemistry

1. Transition Metal Chemistry

2. Transition Metals The atom or one of its common ions must have an incomplete d subshell. The second half of the rule allows Cu ([Ar]4s13d10) to be counted as a transition metal. (There are many reasons to believe it should be.) Zn, Cd, and Hg are not usually considered to be transition metals.

3. What is a transition metal? “an element with valance d- or f-electrons” ie. a d-block or f-block metal

5. biological activity geometry coordination number medical applications magnetic behaviour color What’s interesting about Transition Metal Complexes?? oxidation states

6. 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

7. Main Group Metals vs Transition Metals Just look at these samples of metal solutions across the third row of the periodic table ... What trends do you see? Counting valence d electrons ... Sc2O3 TiO2 VSO4 NaCrO4 MnCl2 K3Fe(CN)6 CoCl2 Ni(NO3)2 CuSO4 ZnSO4

8. Colour of transition metal complexes Ruby Corundum Al2O3 with Cr3+ impurities Sapphire Corundum Al2O3 with Fe2+ and Ti4+ impurities octahedral metal centre coordination number 6 Emerald Beryl AlSiO3 containing Be with Cr3+ impurities

9. 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

10. O2 Haemoglobin Oxygen carrier in blood Porphyrin-Fe transition metal complex Fe(II) ion is octahedrally coordinated Coordination number 6

11. Cisplatin [PtCl2(NH3)2] square planar Pt(II) coordination number 4 cis-isomer the first of a series of platinum coordination complex-based anti-cancer drugs (Platinol-AQ)

12. d orbital splitting in a typical transition metal atom

13. Sc 4s2d1 Ti 4s2d2 V 4s2d3 Cr 4s1d5 Mn 4s2d5 Fe 4s2d6 Co 4s2d7 Ni 4s2d8 Cu 4s1d10 Zn 4s2d10

14. Orbital Energy levels IN COMPLEXES IN ATOMS E 4p 4p 3d 4s 4s 3d add electrons to 4s before 3d take electrons from 4s before 3d

15. Electron Configurations of Atoms Th ns subshell is always filled before (n-1)d subshell. The exceptions result from the extra stability of d5 and d10 configurations Cr [Ar]4s13d5 Cu [Ar]4s13d10 Pd [Kr]5s04d10 (but not Ni)

16. 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

17. [Ar] 3d7 [Ar] 3d6 [Ar]3d9 Electron Configurations of Ions The electrons in the s subshell are always lost before those in the (n-1)d subshell (no exceptions) Examples: Co2+ Co3+ Cu2+ [Ar]4s23d7 [Ar]4s23d7 [Ar]4s13d10

18. 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

19. 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

20. 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

21. 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

22. 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

23. 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)

24. 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

25. 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

26. 3B 4B 5B 6B 7B 8 8 8 2B +3 common +2 common

27. Analogies CrO42- and SO42- MnO4- and ClO4- VO43- and PO43- TiO2 and SiO2 Rules about oxidation states: Highest: Group # Lowest: (Group #) -8 Highest occur in oxides, oxoanions

28. 1st Row 2nd Row 3rd Row

29. 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

30. Activity of Metals Cu, Ag, Au and Ni, Pd, Pt not very active. (Easy to reduce; hard to oxidize) Other transition metals quite active, but many are protected from oxidation by an oxide coating (like Mg, Al)

32. 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

33. 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

34. 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

35. Main Group Metals vs Transition Metals Manganese ion, physically bonded to water There is a huge difference between the symbols Na+(aq) and Mn+2(aq) ... Sodium ion surrounded by water, attracted by electrostatic attraction

36. Main Group Metals vs Transition Metals There’s the big difference: transition metals are found with other species bonded to them, held by both the ionic and covalent bonding. The most common species are any atom, ion or molecule featuring at least one lone pair of electrons. Ammonia and water are among the most common. Anything attached to the transition metal like this is known as a ligand.